Antisense HEMA1 RNA expression inhibits heme and chlorophyll biosynthesis in arabidopsis

QTL mapping and candidate gene analysis reveal two major loci regulating green leaf color in non-heading Chinese cabbage

KEY MESSAGE

Two major-effect QTL GlcA07.1 and GlcA09.1 for green leaf color were fine mapped into 170.25 kb and 191.41 kb intervals on chromosomes A07 and A09, respectively, and were validated by transcriptome analysis. Non-heading Chinese cabbage (NHCC) is a leafy vegetable with a wide range of green colors. Understanding the genetic mechanism behind broad spectrum of green may facilitate the breeding of high-quality NHCC. Here, we used F2 and F7:8 recombination inbred line (RIL) population from a cross between Wutacai (dark-green) and Erqing (lime-green) to undertake the genetic analysis and quantitative trait locus (QTL) mapping in NHCC. The genetic investigation of the F2 population revealed that the variation of green leaf color was controlled by two recessive genes. Six pigments associated with green leaf color, including total chlorophyll, chlorophyll a, chlorophyll b, total carotenoids, lutein, and carotene were quantified and applied for QTL mapping in the RIL population. A total of 7 QTL were detected across the whole genome. Among them, two major-effect QTL were mapped on chromosomes A07 (GlcA07.1) and A09 (GlcA09.1) corresponding to two QTL identified in the F2 population. The QTL GlcA07.1 and GlcA09.1 were further fine mapped into 170.25 kb and 191.41 kb genomic regions, respectively. By comparing gene expression level and gene annotation, BraC07g023810 and BraC07g023970 were proposed as the best candidates for GlcA07.1, while BraC09g052220 and BraC09g052270 were suggested for GlcA09.1. Two InDel molecular markers (GlcA07.1-BcGUN4 and GlcA09.1-BcSG1) associated with BraC07gA023810 and BraC09g052220 were developed and could effectively identify leaf color in natural NHCC accessions, suggesting their potential for marker-assisted leaf color selection in NHCC breeding.

Genome-Wide Analysis of the GLK Gene Family and Its Expression at Different Leaf Ages in the Citrus Cultivar Kanpei

The GLK gene family plays a crucial role in the regulation of chloroplast development and participates in chlorophyll synthesis. However, the precise mechanism by which GLK contributes to citrus's chlorophyll synthesis remains elusive. The GLK gene family causes variations in the photosynthetic capacity and chlorophyll synthesis of different citrus varieties. In this study, we identified tissue-specific members and the key CcGLKs involved in chlorophyll synthesis. A total of thirty CcGLK transcription factors (TFs) were discovered in the citrus genome, distributed across all nine chromosomes. The low occurrence of gene tandem duplication events and intronic variability suggests that intronic variation may be the primary mode of evolution for CcGLK TFs. Tissue-specific expression patterns were observed for various GLK family members; for instance, CcGLK12 and CcGLK15 were specifically expressed in the skin, while CcGLK30 was specific to the ovary, and CcGLK10, CcGLK6, CcGLK21, CcGLK2, CcGLK18, CcGLK9, CcGLK28, and CcGLK8 were specifically expressed in the leaves. CcGLK4, CcGLK5, CcGLK11, CcGLK23, CcGLKl7, CcGLK26, and CcGLK20 may participate in the regulation of the ALA, prochlorophylate, protoporphyrin IX, Mg-protoporphyrin IX, Chl b, T-Chl, MG-ProtoIX ME, and POR contents in citrus.

ZmGluTR1 is involved in chlorophyll biosynthesis and is essential for maize development

Chlorophyll is the most important carrier of photosynthesis in plants and is therefore vital for plant growth and development. Synthesis of 5-aminolevulinic acid (ALA) is initiated and catalyzed by glutamyl-tRNA reductase (GluTR) and is the rate-limiting step in chlorophyll biosynthesis. GluTR is controlled by several regulating factors. Although many studies have investigated the structure and function of GluTR in plants, the maize (Zea mays L.) GluTR has not yet been reported. Here, we isolated and identified the first loss-of-function mutant of GluTR in plants from a maize mutagenic population. The stop-gain mutation in ZmGluTR1 resulted in leaf etiolation throughout the growing season. The level of intermediates of chlorophyll biosynthesis and photosynthetic pigments decreased markedly and abnormal chloroplast structure was also observed in the mutants. Further analysis revealed that the deletion of carboxyl terminal (C-terminal) led to premature transcription termination and this hindered the interaction with FLUORESCENT (FLU), thereby influencing the stability of mutated ZmGluTR1 and leading to abolish interaction with GluTR-binding protein (GluBP). Moreover, mutations in the catalytic domain or nicotinamide adenine dinucleotide phosphate (NADPH) binding domain were lethal under normal growth conditions. These results indicate that ZmGluTR1 plays a fundamental role in chlorophyll biosynthesis and maize development.

Mechanisms for leaf color changes in Osmanthus fragrans 'Ziyan Gongzhu' using physiology, transcriptomics and metabolomics

BACKGROUND

Color-leaved O. fragrans is a variety of Osmanthus fragrans, which has both the fragrance of Osmanthus and the color of color-leaved plants. However, the molecular mechanism of color change of color-leaved O. fragrans is not clear. In this study, we analyzed the regulatory mechanism of four different color leaves of 'Ziyan Gongzhu' through physiological, transcriptome and metabolome levels.

RESULTS

Firstly, we measured the leaf pigments content and leaf chromatic parameters for correlation analysis, indicating a significant correlation between them. Overall, the content of chlorophyll a + b is low and the content of anthocyanin is high in T1 and T2 leaves, along with low expression of chlorophyll synthesis genes (HEMA, CHLG, and CAO, etc.) and high expression of anthocyanin synthesis genes (F3H, F3'H, DFR and ANS, etc.), resulting purple red and light purple in T1 and T2 leaves, respectively. It was also found that the pigment closely related to the color leaves of 'Ziyan Gongzhu' was cyanidin. The content anthocyanins, may be regulated by two putative MYB activators (OfMYB3 and OfMYB4) and two putative MYB repressors (OfMYB1 and OfMYB2). In contrast, the content of chlorophyll a + b is high and the content of anthocyanin is low in T3 and T4 leaves, along with high expression of chlorophyll synthesis genes and low expression of anthocyanin synthesis genes, resulting yellow green and dark green in T3 and T4 leaves, respectively. And abnormal chloroplast development affects chlorophyll content in T1, T2, and T3 leaves. Although the content of carotenoids first dropped in T2 leaves, it then rapidly accumulated in T4 leaves, in sync with the increase in the expression of genes related to carotenoid biosynthesis (ZDS, LHYB, and ZEP, for example). Analysis of photosynthetic, carbohydrate and hormone-related differentially abundant metabolites (DAMs) and DEGs found that they may participate in the regulation of leaf color change of 'Ziyan Gongzhu' by affecting pigment synthesis.

CONCLUSION

Our results pave the way for a comprehensive knowledge of the regulatory processes governing leaf color in 'Ziyan Gongzhu' and identify possible genes for application regarding molecular colored-leaf cultivar breeding.

Comparative physicochemical, hormonal, transcriptomic and proteomic analyses provide new insights into the formation mechanism of two chemotypes of Pogostemon cablin

Patchouli (Pogostemon cablin) is an aromatic plant, and its oil has diverse applications in medicine, food, and cosmetics. Patchouli alcohol is the principal bioactive constituent of its volatile oil. In China, patchouli is typically categorized into two types: patchoulol-type (PA-type) and pogostone-type (PO-type). The study evaluated physiological and biochemical indicators, phytohormone metabolites and conducted transcriptome and proteome analyses on both two chemotypes. The PA-type exhibited higher levels of chlorophyll a, b, and carotenoids than the PO-type. In total, 35 phytohormone metabolites representing cytokinin, abscisic acid, gibberellin, jasmonic acid, and their derivatives were identified using UPLC-MS/MS, 10 of which displayed significant differences, mainly belong to cytokinins and jasmonates. Transcriptome analysis identified 4,799 differentially expressed genes (DEGs), while proteome analysis identified 150 differentially expressed proteins (DEPs). Regarding the transcriptome results, the DEGs of the PO-type showed significant downregulation in the pathways of photosynthesis, photosynthesis-antenna protein, porphyrin and chlorophyll metabolism, carotenoid biosynthesis, sesquiterpene and triterpenoid biosynthesis, and starch and sucrose metabolism, but upregulation in the pathway of zeatin synthesis. A combination of transcriptome and proteome analyses revealed that the DEGs and DEPs of lipoxygenase (LOX2), β-glucosidase, and patchouli synthase (PTS) were collectively downregulated, while the DEGs and DEPs of Zeatin O-xylosyltransferase (ZOX1) and α-amylase (AMY) were jointly upregulated in the PO-type compared to the PA-type. Differential levels of phytohormones, variations in photosynthetic efficiency, and differential expression of genes in the sesquiterpene synthesis pathway may account for the morphological and major active component differences between the two chemotypes of patchouli. The findings of this study offer novel perspectives on the underlying mechanisms contributing to the formation of the two patchouli chemotypes.

FsHemF is involved in the formation of yellow Forsythia leaves by regulating chlorophyll synthesis in response to light intensity

The leaves of Forsythia koreana 'Suwon Gold' are yellow under natural light condition and can revert to green when the light intensity is reduced. To understand the molecular mechanism of leaf color changes in response to light intensity, we compared the chlorophyll content and precursor content between yellow- and green-leaf Forsythia under shade and light-recovery conditions. We identified the conversion of coproporphyrin III (Coprogen III) to protoporphyrin IX (Proto IX) as the primary rate-limiting step of chlorophyll biosynthesis in yellow-leaf Forsythia. Further analysis of the activity of the enzymes that catalyze this step and the expression pattern of the chlorophyll biosynthesis-related genes under different light intensities revealed that the negatively regulated expression of FsHemF by light intensity was the major cause affecting the leaf color change in response to light intensity in yellow-leaf Forsythia. To further understand the cause of differential expression pattern of FsHemF in yellow- and green-leaf lines, we compared the coding sequence and promoter sequence of FsHemF between yellow- and green-leaf Forsythia. We found that one G-box light-responsive cis-element was absent in the promoter region of green-leaf lines. To investigate the functional role of FsHemF, we performed virus-induced gene silencing (VIGS) of FsHemF in green-leaf Forsythia, which leads to yellowing leaf veins, decreased chlorophyll b content, and inhibition of chlorophyll biosynthesis. The results will assist in elucidating the mechanism of yellow-leaf Forsythia in response to light intensity.

STAY-GREEN Accelerates Chlorophyll Degradation in Magnolia sinostellata under the Condition of Light Deficiency

Species of the Magnoliaceae family are valued for their ornamental qualities and are widely used in landscaping worldwide. However, many of these species are endangered in their natural environments, often due to being overshadowed by overstory canopies. The molecular mechanisms of Magnolia's sensitivity to shade have remained hitherto obscure. Our study sheds light on this conundrum by identifying critical genes involved in governing the plant's response to a light deficiency (LD) environment. In response to LD stress, Magnolia sinostellata leaves were endowed with a drastic dwindling in chlorophyll content, which was concomitant to the downregulation of the chlorophyll biosynthesis pathway and upregulation in the chlorophyll degradation pathway. The STAY-GREEN (MsSGR) gene was one of the most up-regulated genes, which was specifically localized in chloroplasts, and its overexpression in Arabidopsis and tobacco accelerated chlorophyll degradation. Sequence analysis of the MsSGR promoter revealed that it contains multiple phytohormone-responsive and light-responsive cis-acting elements and was activated by LD stress. A yeast two-hybrid analysis resulted in the identification of 24 proteins that putatively interact with MsSGR, among which eight were chloroplast-localized proteins that were significantly responsive to LD. Our findings demonstrate that light deficiency increases the expression of MsSGR, which in turn regulates chlorophyll degradation and interacts with multiple proteins to form a molecular cascade. Overall, our work has uncovered the mechanism by which MsSGR mediates chlorophyll degradation under LD stress conditions, providing insight into the molecular interactions network of MsSGR and contributing to a theoretical framework for understanding the endangerment of wild Magnoliaceae species.

Function of ALA Content in Porphyrin Metabolism Regulation of Ananas comosus var. bracteatus

Chlorophyll and heme are essential molecules for photosynthesis and respiration, which are competing branches of the porphyrin metabolism pathway. Chlorophyll and heme balance regulation is very important for the growth and development of plants. The chimeric leaves of Ananas comosus var. bracteatus were composed of central photosynthetic tissue (PT) and marginal albino tissue (AT), which were ideal materials for the study of porphyrin metabolism mechanisms. In this study, the regulatory function of ALA content on porphyrin metabolism (chlorophyll and heme balance) was revealed by comparing PT and AT, 5-Aminolevulinic Acid (ALA) exogenous supply, and interference of hemA expression. The AT remained similar in porphyrin metabolism flow level to the PT by keeping an equal ALA content in both tissues, which was very important for the normal growth of the chimeric leaves. As the chlorophyll biosynthesis in AT was significantly inhibited, the porphyrin metabolism flow was directed more toward the heme branch. Both tissues had similar Mg2+ contents; however, Fe2+ content was significantly increased in the AT. The chlorophyll biosynthesis inhibition in the white tissue was not due to a lack of Mg2+ and ALA. A 1.5-fold increase in ALA content inhibited chlorophyll biosynthesis while promoting heme biosynthesis and hemA expression. The doubling of ALA content boosted chlorophyll biosynthesis while decreasing hemA expression and heme content. HemA expression interference resulted in a higher ALA content and a lower chlorophyll content, while the heme content remained at a relatively low and stable level. Conclusively, a certain amount of ALA was important for the stability of porphyrin metabolism and the normal growth of plants. The ALA content appears to be able to regulate chlorophyll and heme content by bidirectionally regulating porphyrin metabolism branch direction.

Transcriptome and Metabolome Analysis of a Late-Senescent Vegetable Soybean during Seed Development Provides New Insights into Degradation of Chlorophyll

(1) Background: Senescence represents the final stage of plant growth and development, which transfers nutrients to growing seeds and directly affects the yield and quality of crops. However, little is known about chlorophyll degradation in developing and maturing seeds, in contrast to leaf senescence; (2) Methods: RNA-Seq was used to analyze the differentially expressed genes of different late-senescent germplasms. A widely untargeted metabolic analysis was used to analyze differential metabolites. In addition, qRT-PCR was conducted to detect gene expression levels; (3) Results: Transcriptome analysis revealed that ZX12 seeds have a higher expression level of the chlorophyll synthesis genes in the early stage of maturity, compared with ZX4, and have a lower expression level of chlorophyll degradation genes in the late stage of maturity. Flavonoids were the primary differential metabolites, and ZX12 contains the unique and highest expression of three types of metabolites, including farrerol-7-O-glucoside, cyanidin-3-o-(6'-o-feruloyl) glucoside, and kaempferide-3-o-(6'-malonyl) glucoside. Among them, farrerol-7-O-glucoside and cyanidin-3-o-(6'-o-feruloyl) glucoside are flavonoid derivatives containing mono and dihydroxy-B-ring chemical structures, respectively; and (4) Conclusions: It is speculated that the two metabolites can slow down the degradation process of chlorophyll by scavenging oxygen-free radicals in the chloroplast.

Dynamic transcriptome and network-based analysis of yellow leaf mutant Ginkgo biloba

BACKGROUND

Golden leaf in autumn is a prominent feature of deciduous tree species like Ginkgo biloba L., a landscape tree widely cultivated worldwide. However, little was known about the molecular mechanisms of leaf yellowing, especially its dynamic regulatory network. Here, we performed a suite of comparative physiological and dynamic transcriptional analyses on the golden-leaf cultivar and the wild type (WT) ginkgo to investigate the underlying mechanisms of leaf yellowing across different seasons.

RESULTS

In the present study, we used the natural bud mutant cultivar with yellow leaves "Wannianjin" (YL) as materials. Physiological analysis revealed that higher ratios of chlorophyll a to chlorophyll b and carotenoid to chlorophyll b caused the leaf yellowing of YL. On the other hand, dynamic transcriptome analyses showed that genes related to chlorophyll metabolism played key a role in leaf coloration. Genes encoding non-yellow coloring 1 (NYC1), NYC1-like (NOL), and chlorophyllase (CLH) involved in the degradation of chlorophyll were up-regulated in spring. At the summer stage, down-regulated HEMA encoding glutamyl-tRNA reductase functioned in chlorophyll biosynthesis, while CLH involved in chlorophyll degradation was up-regulated, causing a lower chlorophyll accumulation. In carotenoid metabolism, genes encoding zeaxanthin epoxidase (ZEP) and 9-cis-epoxy carotenoid dioxygenase (NCED) showed significantly different expression levels in the WT and YL. Moreover, the weighted gene co-expression network analysis (WGCNA) suggested that the most associated transcriptional factor, which belongs to the AP2/ERF-ERF family, was engaged in regulating pigment metabolism. Furthermore, quantitative experiments validated the above results.

CONCLUSIONS

By comparing the golden-leaf cultivar and the wide type of ginkgo across three seasons, this study not only confirm the vital role of chlorophyll in leaf coloration of YL but also provided new insights into the seasonal transcriptome landscape and co-expression network. Our novel results pinpoint candidate genes for further wet-bench experiments in tree species.

Genetic manipulation of bermudagrass photosynthetic biosynthesis using Agrobacterium-mediated transformation

Bermudagrass is one of the most extensively used warm-season grasses. It is widely used in landscaping, stadium construction and soil remediation due to its excellent regeneration, trampling and stress tolerances. However, studies on its regulatory mechanism and variety improvement by genetic engineering are still at a standstill, owing to its genetic variability and intrinsic limits linked with some resistance to Agrobacterium infection. In this study, we established a higher efficient Agrobacterium-mediated transformation via screening for vital embryogenic callus and improving infection efficiency. The superior callus was light yellow, hard granular and compact, determined with a differentiation rate of more than 95%. The optimized infestation courses by gentle shaking, vacuuming and sonicating were used. The infested calluses were co-cultured for 3 days, followed by desiccation treatments for 1 day to get higher infection efficiency. Then the CdHEMA1 gene, essential for chlorophyll biosynthesis, was cloned and transferred into bermudagrass to validate the aforementioned optimization procedures integrally. Molecular-level analyses indicated that the CdHEMA1 gene had successfully integrated and was greatly increased in transgenic seedlings. Results of the photosynthetic capacity assessment showed that CdHEMA1 overexpression may considerably enhance the contents of photosynthetic pigments, OJIP curve and reaction center density (RC/CSo) to absorb (ABS/CSo, ABS/CSM) and capture (TRo/CSo) more light energy, hence improve the performance indices PI_ABS and PI_CS compared to the wild type. The successful completion of this project would provide a solid platform for further gene function study and molecular breeding of bermudagrass.

Physiological and transcriptome analysis reveals the differences in nitrate content between lamina and midrib of flue-cured tobacco

Nitrate is an important precursor of tobacco-specific nitrosamines (TSNAs) and a remarkable difference in nitrate accumulation between lamina and midrib of flue-cured tobacco has long been observed. However, the physiological and molecular mechanisms underpinning this difference remain poorly understood. In this study, physiological and genetic factors impacting nitrate accumulation were identified in pot experiments using flue-cured tobacco K326 with contrasting nitrate content between lamina and midrib. The results showed that three times higher NO3-N content was observed in midrib than that in the lamina, along with lower pigment, NH4-N content, nitrate reductase activity (NRA), sucrose synthetase activity (SSA), and glutamine synthetase activity (GSA) in midrib. Transcriptome analysis revealed that expression of genes involved in porphyrin and chlorophyll metabolism, carotenoid biosynthesis, photosynthesis-antenna proteins, photosynthesis, carbon fixation in photosynthetic organisms, starch and sucrose metabolism, nitrogen metabolism, and biosynthesis of amino acids were significantly lower in midrib than in lamina. qRT-PCR results showed that the expression level of nitrate transporter genes LOC107782967, LOC107806749, LOC107775674, LOC107829632, LOC107799198, LOC107768465 decreased by 2.74, 1.81, 49.5, 3.5, 2.64 and 2.96-folds while LOC107789301 increased by 8.23-folds in midrib but not in lamina. Reduced chlorophyll content might result in low carbohydrate formation which is the source of energy and carbon skeleton supply, then the low capacity of nitrogen reduction, assimilation and transportation, and the poor ability of nitrate reallocation but the high capacity of accumulation might lead to nitrate accumulation in midrib. The results laid the foundation for reducing nitrate content and TSNA formation in tobacco midribs and their products.

Transcription Profiles Reveal Age-Dependent Variations of Photosynthetic Properties and Sugar Metabolism in Grape Leaves (Vitis vinifera L.)

Leaves, considered as the ‘source’ organs, depend on the development stages because of the age-dependent photosynthesis and assimilation of leaves. However, the molecular mechanisms of age-dependent limitations on the function of leaves are seldom reported. In the present study, the photosynthesis-related characteristics and photoassimilates were investigated in grape leaves at six different age groups (Ll to L6) at micro-morphological, biochemical, and molecular levels. These results showed lower expression levels of genes associated with stomatal development, and chl biosynthesis resulted in fewer stomata and lowered chlorophyll a/b contents in L1 when compared to L3 and L5. The DEGs between L5 and L3/L1 were largely distributed at stomatal movement, carbon fixation, and sucrose and starch metabolism pathways, such as STOMATAL ANION CHANNEL PROTEIN 1 (SLAC1), FRUCTOSE-1,6-BISPHOSPHATE ALDOLASE (FBA1), SUCROSE-PHOSPHATE SYNTHASE (SPP1), and SUCROSE-PHOSPHATE PHOSPHATASE (SPS2, 4). These genes could be major candidate genes leading to increased photosynthesis capacity and sugar content in L5. The accumulation of starch grains in the chloroplast and palisade tissue of L5 and higher transcription levels of genes related to starch biosynthesis in L5 further supported the high ability of L5 to produce photoassimilates. Hence, our results provide insights for understanding different photosynthetic functions in age-dependent leaves in grape plants at the molecular level.

Cytological, Biochemical, and Transcriptomic Analyses of a Novel Yellow Leaf Variation in a Paphiopedilum (Orchidaceae) SCBG COP15

The genus Paphiopedilum, belonging to the Orchidaceae, has high ornamental value. Leaf variations can considerably improve the economic and horticultural value of the orchids. In the study, a yellow leaf mutant of a Paphiopedilum hybrid named P. SCBG COP15 was identified during the in vitro plant culture process; however, little is known about their molecular mechanisms. For this, RNA-seq libraries were created and used for the transcriptomic profiling of P. SCBG COP15 and the yellow mutant. The Chl a, Chl b, and carotenoid contents in the yellow leaves decreased by approximately 75.99%, 76.92%, and 56.83%, respectively, relative to the green leaves. Decreased chloroplasts per cell and abnormal chloroplast ultrastructure were observed by electron microscopic investigation in yellowing leaves; photosynthetic characteristics and Chl fluorescence parameters were also decreased in the mutant. Altogether, 34,492 unigenes were annotated by BLASTX; 1,835 DEGs were identified, consisting of 697 upregulated and 1138 downregulated DEGs. HEMA, CRD, CAO, and CHLE, involved in Chl biosynthesis, were predicted to be key genes responsible for leaf yellow coloration. Our findings provide an essential genetic resource for understanding the molecular mechanism of leaf color variation and breeding new varieties of Paphiopedilum with increased horticultural value.

Biochemical and transcriptomic analyses reveal that critical genes involved in pigment biosynthesis influence leaf color changes in a new sweet osmanthus cultivar 'Qiannan Guifei'

Background

Osmanthus fragrans (Oleaceae) is one of the most important ornamental plant species in China. Many cultivars with different leaf color phenotypes and good ornamental value have recently been developed. For example, a new cultivar ‘Qiannan Guifei’, presents a rich variety of leaf colors, which change from red to yellow-green and ultimately to green as leaves develop, making this cultivar valuable for landscaping. However, the biochemical characteristics and molecular mechanisms underlying leaf color changes of these phenotypes have not been elucidated. It has been hypothesized that the biosynthesis of different pigments in O. fragrans might change during leaf coloration. Here, we analyzed transcriptional changes in genes involved in chlorophyll (Chl), flavonoid, and carotenoid metabolic pathways and identified candidate genes responsible for leaf coloration in the new cultivar ‘Qiannan Guifei’.

Methods

Leaf samples were collected from ‘Qiannan Guifei’ plants at the red (R), yellow-green (YG) and green (G) leaf stages. We compared the different-colored leaves via leaf pigment concentrations, chloroplast ultrastructure, and transcriptomic data. We further analyzed differentially expressed genes (DEGs) involved in the Chl, flavonoid, and carotenoid metabolic pathways. In addition, we used qRT-PCR to validate expression patterns of the DEGs at the three stages.

Results

We found that, compared with those at the G stage, chloroplasts at the R and YG stages were less abundant and presented abnormal morphologies. Pigment analyses revealed that the leaves had higher flavonoid and anthocyanin levels at the R stage but lower Chl and carotenoid concentrations. Similarly, Chl and carotenoid concentrations were lower at the YG stage than at the G stage. By using transcriptomic sequencing, we further identified 61 DEGs involved in the three pigment metabolic pathways. Among these DEGs, seven structural genes (OfCHS, OfCHI, OfF3H, OfDFR, OfANS, OfUGT andOf3AT) involved in the flavonoid biosynthesis pathway were expressed at the highest level at the R stage, thereby increasing the biosynthesis of flavonoids, especially anthocyanins. Six putativeOfMYB genes, including three flavonoid-related activators and three repressors, were also highly expressed at the R stage, suggesting that they might coordinately regulate the accumulation of flavonoids, including anthocyanins. Additionally, expressions of the Chl biosynthesis-related genes OfHEMA, OfCHLG and OfCAO and the carotenoid biosynthesis-related genes OfHYB and OfZEP were upregulated from the R stage to the G stage, which increased the accumulation of Chl and carotenoids throughout leaf development. In summary, we screened the candidate genes responsible for the leaf color changes of ‘Qiannan Guifei’, improved current understanding of the regulatory mechanisms underlying leaf coloration and provided potential targets for future leaf color improvement in O. fragrans.

Mapping of a Pale Green Mutant Gene and Its Functional Verification by Allelic Mutations in Chinese Cabbage (Brassica rapa L. ssp. pekinensis)

Leaves are the main organ for photosynthesis, and variations in leaf color affect photosynthesis and plant biomass formation. We created two similar whole-plant pale green mutants (pem1 and pem2) from the double haploid (DH) Chinese cabbage line "FT" through ethyl methanesulfonate (EMS) mutagenesis of seeds. Photosynthetic pigment contents and net photosynthetic rates were significantly lower in the mutants than in the wild-type "FT," and the chloroplast thylakoid endomembrane system was poor. Genetic analysis showed that the mutated phenotypes of pem1 and pem2 were caused by a single nuclear gene. Allelism tests showed that pem1 and pem2 were alleles. We mapped Brpem1 to a 64.25 kb region on chromosome A10, using BSR-Seq and map-based cloning of 979 F₂ recessive individuals. Whole-genome re-sequencing revealed a single nucleotide polymorphism (SNP) transition from guanine to adenosine on BraA10g021490.3C in pem1, causing an amino acid shift from glycine to glutamic acid (G to E); in addition, BraA10g021490.3C in pem2 was found to have a single nucleotide substitution from guanine to adenosine, causing an amino acid change from E to lysine (K). BraA10g021490.3C is a homolog of the Arabidopsisdivinyl chlorophyllide a 8-vinyl-reductase (DVR) gene that encodes 3,8-divinyl protochlorophyllide a 8-vinyl reductase, which is a key enzyme in chlorophyll biosynthesis. Enzyme activity assay and chlorophyll composition analysis demonstrated that impaired DVR had partial loss of function. These results provide a basis to understand chlorophyll metabolism and explore the mechanism of a pale green phenotype in Chinese cabbage.

A genome wide transcriptional study of Populus alba x P. tremula var. glandulosa in response to nitrogen deficiency stress

Poplar 84 K (Populus alba x P. tremula var. glandulosa) is a good resource for genetic engineering due to its rapid growth and wide adaptability, and it is also an excellent ornamental tree species. In this study, we used 84 K plantlets grown in the nitrogen-limited medium as experimental materials to explore the molecular mechanism in 84 K leaves under nitrogen deficiency. A total of 5,868 differentially expressed genes (DEGs) were identified using the transcriptional information from RNA-seq data. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment results revealed that the DEGs were mainly involved in energy metabolism and anthocyanin biosynthesis. We then identified differentially expressed transcription factors (TFs) and constructed TF centered gene co-expression networks for chlorophyll and anthocyanin biosynthesis pathway genes. Twenty potential regulators were finally identified. We speculated the transcription factors that control the pigmentation in leaves with the MYB-bHLH-WD40 (MBW) pigment regulatory model. Such identification will clarify the genetic basis of the secondary metabolism in 84 K, and being a source of candidate genes for future plant genetic engineering. Our work broadens the researchers' understanding of the regulation of anthocyanin synthesis in trees and provides new perspectives for ornamental 84 K poplar breeding.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01012-3.

Cold acclimation can specifically inhibit chlorophyll biosynthesis in young leaves of Pakchoi

BACKGROUND

Leaf color is an important trait in breeding of leafy vegetables. Y-05, a pakchoi (Brassica rapa ssp. chinensis) cultivar, displays yellow inner (YIN) and green outer leaves (GOU) after cold acclimation. However, the mechanism of this special phenotype remains elusive.

RESULTS

We assumed that the yellow leaf phenotype of Y-05 maybe caused by low chlorophyll content. Pigments measurements and transmission electron microscopy (TEM) analysis showed that the yellow phenotype is closely related with decreased chlorophyll content and undeveloped thylakoids in chloroplast. Transcriptomes and metabolomes sequencing were next performed on YIN and GOU. The transcriptomes data showed that 4887 differentially expressed genes (DEGs) between the YIN and GOU leaves were mostly enriched in the chloroplast- and chlorophyll-related categories, indicating that the chlorophyll biosynthesis is mainly affected during cold acclimation. Together with metabolomes data, the inhibition of chlorophyll biosynthesis is contributed by blocked 5-aminolevulinic acid (ALA) synthesis in yellow inner leaves, which is further verified by complementary and inhibitory experiments of ALA. Furthermore, we found that the blocked ALA is closely associated with increased BrFLU expression, which is indirectly altered by cold acclimation. In BrFLU-silenced pakchoi Y-05, cold-acclimated leaves still showed green phenotype and higher chlorophyll content compared with control, meaning silencing of BrFLU can rescue the leaf yellowing induced by cold acclimation.

CONCLUSIONS

Our findings suggested that cold acclimation can indirectly promote the expression of BrFLU in inner leaves of Y-05 to block ALA synthesis, resulting in decreased chlorophyll content and leaf yellowing. This study revealed the underlying mechanisms of leaves color change in cold-acclimated Y-05.

Interpreting Cytokinin Action as Anterograde Signaling and Beyond

Among the major phytohormones, the cytokinin exhibits unique features for its ability to positively affect the developmental status of plastids. Even early on in its research, cytokinins were known to promote plastid differentiation and to reduce the loss of chlorophyll in detached leaves. Since the discovery of the components of cytokinin perception and primary signaling, the genes involved in photosynthesis and plastid differentiation have been identified as those directly targeted by type-B response regulators. Furthermore, cytokinins are known to modulate versatile cellular processes such as promoting the division and differentiation of cells and, in concert with auxin, initiating the de novo formation of shoot apical meristem (SAM) in tissue cultures. Yet how cytokinins precisely participate in such diverse cellular phenomena, and how the associated cellular processes are coordinated as a whole, remains unclear. A plausible presumption that would account for the coordinated gene expression is the tight and reciprocal communication between the nucleus and plastid. The fact that cytokinins affect plastid developmental status via gene expression in both the nucleus and plastid is interpreted here to suggest that cytokinin functions as an initiator of anterograde (nucleus-to-plastid) signaling. Based on this viewpoint, we first summarize the physiological relevance of cytokinins to the coordination of plastid differentiation with de novo shoot organogenesis in tissue culture systems. Next, the role of endogenous cytokinins in influencing plastid differentiation within the SAM of intact plants is discussed. Finally, a presumed plastid-derived signal in response to cytokinins for coupled nuclear gene expression is proposed.

Perspectives on improving light distribution and light use efficiency in crop canopies

Plant stands in nature differ markedly from most seen in modern agriculture. In a dense mixed stand, plants must vie for resources, including light, for greater survival and fitness. Competitive advantages over surrounding plants improve fitness of the individual, thus maintaining the competitive traits in the gene pool. In contrast, monoculture crop production strives to increase output at the stand level and thus benefits from cooperation to increase yield of the community. In choosing plants with higher yields to propagate and grow for food, humans may have inadvertently selected the best competitors rather than the best cooperators. Here, we discuss how this selection for competitiveness has led to overinvestment in characteristics that increase light interception and, consequently, sub-optimal light use efficiency in crop fields that constrains yield improvement. Decades of crop canopy modeling research have provided potential strategies for improving light distribution in crop canopies, and we review the current progress of these strategies, including balancing light distribution through reducing pigment concentration. Based on recent research revealing red-shifted photosynthetic pigments in algae and photosynthetic bacteria, we also discuss potential strategies for optimizing light interception and use through introducing alternative pigment types in crops. These strategies for improving light distribution and expanding the wavelengths of light beyond those traditionally defined for photosynthesis in plant canopies may have large implications for improving crop yield and closing the yield gap.

Effect of chlorophyll biosynthesis-related genes on the leaf color in Hosta (Hosta plantaginea Aschers) and tobacco (Nicotiana tabacum L.)

BACKGROUND

'Regal Splendour' (Hosta variety) is famous for its multi-color leaves, which are useful resources for exploring chloroplast development and color changes. The expressions of chlorophyll biosynthesis-related genes (HrHEMA, HrPOR and HrCAO) in Hosta have been demonstrated to be associated with leaf color. Herein, we isolated, sequenced, and analyzed HrHEMA, HrPOR and HrCAO genes. Subcellular localization was also performed to determine the location of the corresponding enzymes. After plasmid construction, virus-induced gene silencing (VIGS) was carried out to reduce the expressions of those genes. In addition, HrHEMA-, HrPOR- and HrCAO-overexpressing tobacco plants were made to verify the genes function. Changes of transgenic tobacco were recorded under 2000 lx, 6000 lx and 10,000 lx light intensity. Additionally, the contents of enzyme 5-aminolevulinic acid (5-ALA), porphobilinogen (PBG), chlorophyll a and b (Chla and Chlb), carotenoid (Cxc), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), proline (Pro) and catalase (CAT) under different light intensities were evaluated.

RESULTS

The silencing of HrHEMA, HrPOR and HrCAO genes can induce leaf yellowing and chloroplast structure changes in Hosta. Specifically, leaves of Hosta with HrCAO silencing were the most affected, while those with HrPOR silencing were the least affected. Moreover, all three genes in tobacco were highly expressed, whereas no expression was detected in wild-type (WT). However, the sensitivities of the three genes to different light intensities were different. The highest expression level of HrHEMA and HrPOR was detected under 10,000 lx of illumination, while HrCAO showed the highest expression level under 6000 lx. Lastly, the 5-ALA, Chla, Cxc, SOD, POD, MDA, Pro and CAT contents in different transgenic tobaccos changed significantly under different light intensities.

CONCLUSION

The overexpression of these three genes in tobacco enhanced photosynthesis by accumulating chlorophyll content, but the influential level varied under different light intensities. Furthermore, HrHEMA-, HrPOR- and HrCAO- overexpressing in tobacco can enhance the antioxidant capacity of plants to cope with stress under higher light intensity. However, under lower light intensity, the antioxidant capacity was declined in HrHEMA-, HrPOR- and HrCAO- overexpressing tobaccos.

Comparative proteomic analysis of Prunella vulgaris L. spica ripening

Prunella vulgaris L., better known as 'self-heal', has been extensively used in the traditional system of medicines. To reveal the regulatory mechanism of its development, TMT-based quantitative proteome analysis was performed in the Prunella vulgaris L. spica before and during ripening (Group A and Group B, respectively). This analysis resulted in the identification of 7655 proteins, of which 1910 showed differential abundance between the two groups. Pronounced changes in the proteomic profile included the following: 1) Stress-responsive proteins involved in protecting cells and promoting fruit ripening and seed development were highly abundant during ripening. 2) The degradation of chlorophyll, inhibition of chlorophyll biosynthesis and increased abundance of transketolase occurred simultaneously in the spica of Prunella vulgaris L., resulting in the spica changing color from green to brownish red. 3) The abundance of protein species related to phenylpropanoid biosynthesis mainly increased during ripening, while flavonoid and terpenoid backbone biosynthesis mostly occurred before ripening. SIGNIFICANCE: This study establishes a link between protein profiles and mature phenotypes, which will help to improve our understanding of the molecular mechanisms involved in the maturation of Prunella vulgaris L. at the proteome level and reveal the scientific connotation for the best time to harvest Prunella vulgaris L. This work provides a scientific basis for the production of high-quality medicinal Prunella vulgaris L., as well as a typical demonstration of molecular research used for the harvest period of traditional Chinese medicine. BIOLOGICAL SIGNIFICANCE: This work provided a comprehensive overview on the functional protein profile changes of Prunella vulgaris L. spica at different growing stages, as well as the scientific rationale of Prunella vulgaris L. harvested in summer after brownish red, thus laid an intriguing stepping stone for elucidating the molecular mechanisms of quality development.

Knock-down of δ-aminolevulinic acid dehydratase via virus-induced gene silencing alters the microRNA biogenesis and causes stress-related reactions in citrus plants

The δ-aminolevulinic acid (δ-ALA) is an intermediate in the biosynthetic pathway of tetrapyrroles. Tetrapyrroles play vital roles in many biological processes such as photosynthesis, respiration, and light-sensing. ALA-dehydratase (ALAD) combines two molecules of δ-ALA to form porphobilinogen. In citrus, the silencing of ALAD caused discrete yellow spots and necrosis in leaves and stems. Additionally, it caused rapid death in developing new shoots. Herein, we hypothesize that the accumulation of δ-ALA results in severe stress and reduced meristem development. For that reason, we investigated the dynamic changes in the expression profiles of 23 microRNA (miRNA) identified through small RNA sequencing, from CTV-tALAD plants in comparison with healthy C. macrophylla and C. macrophylla infiltrated with CTV-wt. Furthermore, we reported the effect of ALAD silencing on the total phenolics, H₂O_2, and reactive oxygen species (ROS) levels, to examine the possibilities of miRNAs involving the regulation of these pathways. Our results showed that the total phenolics content, H₂O₂, and O₂^- levels were increased in CTV-tALAD plants. Moreover, 63 conserved miRNA members belonging to 23 different miRNA families were differentially expressed in CTV-tALAD plants compared to controls. The identified miRNAs are implicated in auxin biosynthesis and signaling, axillary shoot meristem formation and leaf morphology, starch metabolism, and oxidative stress. Collectively, our findings suggested that ALAD silencing initiates stress on citrus plants. As a result, CTV-tALAD plants exhibit reduced metabolic rate, growth, and development in order to cope with the stress that resulted from the accumulation of δ-ALA. This cascade of events led to leaf, stem, and meristem necrosis and failure of new shoot development.

Characterization of a novel allele of bc12/gdd1 indicates a differential leaf color function for BC12/GDD1 in Indica and Japonica backgrounds

Leaf color is directly associated with plant photosynthesis. Here, we have isolated and identified a spontaneous rice mutant named yd1 that has yellowish leaves and dwarf stature. Map-based cloning reveals that YD1 encodes a previously reported kinesin protein from the kinesin-4 subfamily, BC12/GDD1. Arginine-328 is replaced by leucine in yd1, BC12^328Leu. YD1 is mainly expressed in leaves and is involved in chlorophyll (Chl) synthesis. The yd1 mutant had less Chl and a reduced and disordered thylakoid ultrastructure. In yd1 plants, Chl biosynthesis and photosynthesis associated gene expression was decreased and Chl degradation gene expression was increased, thereby leading to a reduced photosynthesis rate and grain yield. In this study we reveal that the novel BC12^328Leu allele of BC12 modulated plant leaf color in yd1 plants, which has not been previously reported in studies of BC12/GDD1/MTD1/SRG1. Gene knockout results indicated that YD1 regulates leaf color in the indica rice background, but not in the japonica rice background. Our study provides new insights into molecular regulation of rice growth by BC12/GDD1 in different genetic backgrounds.

Mutation Mechanism of Leaf Color in Plants: A Review

Color mutation is a common, easily identifiable phenomenon in higher plants. Color mutations usually affect the photosynthetic efficiency of plants, resulting in poor growth and economic losses. Therefore, leaf color mutants have been unwittingly eliminated in recent years. Recently, however, with the development of society, the application of leaf color mutants has become increasingly widespread. Leaf color mutants are ideal materials for studying pigment metabolism, chloroplast development and differentiation, photosynthesis and other pathways that could also provide important information for improving varietal selection. In this review, we summarize the research on leaf color mutants, such as the functions and mechanisms of leaf color mutant-related genes, which affect chlorophyll synthesis, chlorophyll degradation, chloroplast development and anthocyanin metabolism. We also summarize two common methods for mapping and cloning related leaf color mutation genes using Map-based cloning and RNA-seq, and we discuss the existing problems and propose future research directions for leaf color mutants, which provide a reference for the study and application of leaf color mutants in the future.

Regulation of Iron Homeostasis and Use in Chloroplasts

Iron (Fe) is essential for life because of its role in protein cofactors. Photosynthesis, in particular photosynthetic electron transport, has a very high demand for Fe cofactors. Fe is commonly limiting in the environment, and therefore photosynthetic organisms must acclimate to Fe availability and avoid stress associated with Fe deficiency. In plants, adjustment of metabolism, of Fe utilization, and gene expression, is especially important in the chloroplasts during Fe limitation. In this review, we discuss Fe use, Fe transport, and mechanisms of acclimation to Fe limitation in photosynthetic lineages with a focus on the photosynthetic electron transport chain. We compare Fe homeostasis in Cyanobacteria, the evolutionary ancestors of chloroplasts, with Fe homeostasis in green algae and in land plants in order to provide a deeper understanding of how chloroplasts and photosynthesis may cope with Fe limitation.

Silicon improves the growth of cucumber under excess nitrate stress by enhancing nitrogen assimilation and chlorophyll synthesis

Silicon (Si) can increase salt tolerance of plants, and previous studies have focused on NaCl stress; whereas in protected facilities, nitrate (but not NaCl) accumulation is one of the major causes of secondary soil salinization. However, information on Si's effect on plant growth under nitrate stress is very limited, and the underlying mechanism is unknown. Here, we investigated Si's effect on plant growth, nitrogen assimilation and chlorophyll synthesis in cucumber. Cucumber seedlings ('Jinyou 1') were subjected to 200 mM nitrate stress without or with addition of 2 mM Si. The results showed that root application, but not foliar application of Si, could improve cucumber growth under nitrate stress. Root addition of Si increased photosynthetic rate and decreased oxidative damage of stressed plants. Under nitrate stress, Si addition decreased the accumulation of nitrate, nitrite and ammonium, and promoted the activities of nitrate reductase, nitrite reductase, glutamine synthase, glutamine-2-oxoglutarate aminotransferase and glutamate dehydrogenase in leaves. The concentrations of glutamic acid, 5-aminolevulinic acid, porphobilinogen and uroporphyrinogen Ⅲ were increased under nitrate stress, while these were decreased by added Si. Added Si increased the levels of chlorophyll and its precursors (protoporphyrin Ⅸ, Mg-protoporphyrin Ⅸ and protochlorophyllide), and expressions of genes encoding enzymes in chlorophyll synthesis (CHLH, POR and CAO) under nitrate stress. These results suggest that Si could improve cucumber growth under nitrate stress by enhancing nitrogen assimilation and chlorophyll synthesis, and imply an application of Si fertilizer in solving secondary soil salinization in protected facilities.

Biochemical and Comparative Transcriptome Analyses Reveal Key Genes Involved in Major Metabolic Regulation Related to Colored Leaf Formation in Osmanthus fragrans 'Yinbi Shuanghui' during Development

Osmanthus fragrans 'Yinbi Shuanghui' not only has a beautiful shape and fresh floral fragrance, but also rich leaf colors that change, making the tree useful for landscaping. In order to study the mechanisms of color formation in O. fragrans 'Yinbi Shuanghui' leaves, we analyzed the colored and green leaves at different developmental stages in terms of leaf pigment content, cell structure, and transcriptome data. We found that the chlorophyll content in the colored leaves was lower than that of green leaves throughout development. By analyzing the structure of chloroplasts, the colored leaves demonstrated more stromal lamellae and low numbers of granum thylakoid. However, there was a large number of plastoglobuli. Using transcriptome sequencing, we demonstrated that the expression of differentially expressed genes (DEGs) involved in chlorophyll degradation was upregulated, i.e., heme oxygennase-1 (HO1), pheophorbide a oxidase (PAO), and chlorophyllase-2 (CLH2), affecting the synthesis of chlorophyll in colored leaves. The stay-green gene (SGR) was upregulated in colored leaves. Genes involved in carotenoid synthesis, i.e., phytoene synthase 1 (PSY1) and 1-Deoxyxylulose-5-phosphate synthase (DXS), were downregulated in colored leaves, impeding the synthesis of carotenoids. In the later stage of leaf development, the downregulated expression of Golden2-Like (GLK) inhibited chloroplast development in colored leaves. Using weighted gene co-expression network analysis (WGCNA) to investigate the correlation between physiological indicators and DEGs, we chose the modules with the highest degree of relevance to chlorophyll degradation and carotenoid metabolism. A total of five genes (HSFA2, NFYC9, TCP20, WRKY3, and WRKY4) were identified as hub genes. These analyses provide new insights into color formation mechanisms in O. fragrans 'Yinbi Shuanghui' leaves at the transcriptional level.

Color characteristics, pigment accumulation and biosynthetic analyses of leaf color variation in herbaceous peony (Paeonia lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) is one of the color-leaved ornamental spring plants, with graceful appearance and splendid color. However, the underlying mechanism of this coloration variation from purple to green has not been studied in P. lactiflora. In th study, the leaves in purple, purple-green, and green stages were compared in terms of anatomical, physiological, and molecular. We found that the variation of leaf color from purple to green was mainly determined by the change in pigments distributed in the leaf surface. Physiological experiments showed a significant increase in chlorophyll contents and a notable reduction in anthocyanin contents in leaves from the purple to green stages. We further found that the anthocyanin biosynthesis-related dihydroflavonol 4-reductase (DFR) gene and anthocyanin synthase (ANS) gene as well as chlorophyll biosynthesis-related glutamyl-tRNA reductase (HEMA) gene showed a decreased trend in leaves from purple to green stages, whereas the chlorophyll degradation-related chlorophyll b reductase (NYC) gene showed a rising trend. Alteration of DFR and ANS gene expression might reduce anthocyanin accumulation, whereas increased HEMA gene expression would enhance chlorophyll biosynthesis and reduced NYC gene expression would inhibit chlorophyll degradation. Consequently, reduction in anthocyanins and enhanced deposition of chlorophylls resulted in leaf coloration variation from purple to green in P. lactiflora, which could improve our understanding of its mechanism for further studies.

Physiological and Anatomical Differences and Differentially Expressed Genes Reveal Yellow Leaf Coloration in Shumard Oak

Shumard oak (Quercus shumardii Buckley) is a traditional foliage plant, but little is known about its regulatory mechanism of yellow leaf coloration. Here, the yellow leaf variety of Q. shumardii named 'Zhongshan Hongjincai' (identified as 'ZH' throughout this work) and a green leaf variety named 'Shumard oak No. 23' (identified as 'SO' throughout this work) were compared. 'ZH' had lower chlorophyll content and higher carotenoid content; photosynthetic characteristics and chlorophyll fluorescence parameters were also lower. Moreover, the mesophyll cells of 'ZH' showed reduced number of chloroplasts and some structural damage. In addition, transcriptomic analysis identified 39,962 differentially expressed genes, and their expression levels were randomly verified. Expressions of chlorophyll biosynthesis-related glumly-tRNA reductase gene and Mg-chelatase gene were decreased, while pheophorbide a oxygenase gene associated with chlorophyll degradation was up-regulated in 'ZH'. Simultaneously, carotenoid isomerase gene, z-carotene desaturase gene, violaxanthin de-epoxidase gene and zeaxanthin epoxidase gene involved in carotenoid biosynthesis were up-regulated in 'ZH'. These gene expression changes were accompanied by decreased chlorophyll content and enhanced carotenoid accumulation in 'ZH'. Consequently, changes in the ratio of carotenoids to chlorophyll could be driving the yellow leaf coloration in Q. shumardii.

The Effects of Ultraviolet A/B Treatments on Anthocyanin Accumulation and Gene Expression in Dark-Purple Tea Cultivar 'Ziyan' (Camellia sinensis)

‘Ziyan’ is a novel anthocyanin-rich tea cultivar with dark purple young shoots. However, how its anthocyanin accumulation is affected by environmental factors, such as ultraviolet (UV), remains unclear. In this study, we observed that UV light treatments stimulated anthocyanin accumulation in ‘Ziyan’ leaves, and we further analyzed the underlying mechanisms at gene expression and enzyme activity levels. In addition, the catechins and chlorophyll contents of young shoots under different light treatments were also changed. The results showed that the contents of total anthocyanins and three major anthocyanin molecules, i.e., delphinidin, cyanidin, and pelargonidin, were significantly higher in leaves under UV-A, UV-B, and UV-AB treatments than those under white light treatment alone. However, the total catechins and chlorophyll contents in these purple tea plant leaves displayed the opposite trends. The anthocyanin content was the highest under UV-A treatment, which was higher by about 66% than control. Compared with the white light treatment alone, the enzyme activities of chalcone synthase (CHS), flavonoid 3′,5′-hydroxylase (F3′5′H), and anthocyanidin synthase (ANS) under UV treatments increased significantly, whereas the leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) activities reduced. There was no significant difference in dihydroflavonol 4-reductase (DFR) activity under all treatments. Comparative transcriptome analyses unveiled that there were 565 differentially expressed genes (DEGs) of 29,648 genes in three pair-wise comparisons (white light versus UV-A, W vs. UV-A; white light versus UV-B, W vs. UV-A; white light versus UV-AB, W vs. UV-AB). The structural genes in anthocyanin pathway such as flavanone 3-hydroxylase (F3H), F3′5′H, DFR, and ANS, and regulatory gene TT8 were upregulated under UV-A treatment; F3′5′H, DFR, ANS, and UFGT and regulatory genes EGL1 and TT2 were upregulated under UV-AB treatment. However, most structural genes involved in phenylpropanoid and flavonoid pathways were downregulated under UV-B treatment compared with control. The expression of LAR and ANR were repressed in all UV treatments. Our results indicated that UV-A and UV-B radiations can induce anthocyanin accumulation in tea plant ‘Ziyan’ by upregulating the structural and regulatory genes involved in anthocyanin biosynthesis. In addition, UV radiation repressed the expression levels of LAR, ANR, and FLS, resulting in reduced ANR activity and a metabolic flux shift toward anthocyanin biosynthesis.

Comparative Proteomic Analysis Reveals That Chlorophyll Metabolism Contributes to Leaf Color Changes in Wucai ( Brassica campestris L.) Responding to Cold Acclimation

Chlorophyll is a vital photosynthetic pigment that plays a key role in plant development, participating in light energy capture and energy conversion. In this study, a novel wucai ( Brassica campestris L.) germplasm with green outer leaves and yellow inner leaves at the adult stage (W7-2) was used to examine chlorophyll metabolism response to cold acclimation. A green leaf wucai genotype without leaf color changes named W7-1 was selected as the control to evaluate the chlorophyll metabolism changes of W7-2. Compared to W7-1, the contents of chlorophyll a (Chl a) and chlorophyll b (Chl b) in W7-2 were significantly reduced at five developmental stages (13, 21, 29, 37, and 45 days after planting (DAP)). An iTRAQ-based quantitative proteomic analysis was carried out at 21 and 29 DAP according to the leaf color changes in both of genotypes. 1409 proteins were identified, while 218 of them displayed differential accumulations between W7-2 and W7-1 during the two developmental stages. The differentially expressed proteins (DEPs) mainly assigned to chlorophyll biosynthesis, photosynthesis, carbohydrate metabolism, ribosome metabolism and posttranslational modification. Among these DEPs, NADPH-protochlorophyllide oxidoreductase (PORB) and Mg-protoporphyrin IX chelatase 1 (CHLI1) were the key enzymes participating in chlorophyll (Chl) biosynthesis, which was down-regulated at 21 DAP and up-regulated at 29 DAP in W7-2 compared with W7-1, respectively. The expression analysis of genes of three subunits of Mg-chelatase ( CHLI1, CHLD, and CHLH), Genomes Uncoupled 4 ( GUN4), and Thioredoxin ( TRX3) associated with chlorophyll metabolism also displayed significant down-regulation in W7-2. In particular, PORB showed significant up-regulation in W7-2, significantly affecting chlorophyll biosynthesis. Additionally, differences in chlorophyll metabolism between W7-2 and W7-1 were in terms of altered photosynthesis, carbohydrate, and energy metabolism. We found that the transcription levels of most photosynthesis proteins showed significantly lower levels, and the genes expression level, associated with carbohydrate and energy metabolism, were lower in W7-2 than in W7-1. Therefore, the present study results help understand the physiological and molecular mechanisms underlying leaf coloring responding to cold acclimation.

Salicylic acid-altering Arabidopsis plant response to cadmium exposure: Underlying mechanisms affecting antioxidation and photosynthesis-related processes

Previous studies have demonstrated that the genetic modification of basal salicylic acid (SA) level changed Arabidopsis plant response to cadmium (Cd) stress, but the mechanisms remain evaluated. In this study, Arabidopsis wild type (WT) and its SA-reducing transgenic line nahG (naphthalene hydroxylase G), SA-accumulating mutant snc1 (suppressor of nonexpressor of PR gene, constitutive 1) were exposed to 50 μM Cd²⁺ for 48 h or 7 d (just for assessing plant growth). The Cd treatment increased the expression levels of SA biosynthesis-related genes leading to enhanced SA accumulations in plant leaves, which was further confirmed by the expression patterns of SA marker genes. Cadmium accumulation was much higher in the Cd-exposed roots than in leaves, but was not affected by SA levels. Exposure to Cd inhibited plant growth of both aerial parts and roots, to a greater degree in snc1, and a lesser extent in nahG as compared with WT. Although Cd treatment increased plant antioxidative capacity, oxidative damage happened, especially to snc1 plants. Photoinhibition occurred in Cd-stressed plants leading to a decrease in photosynthetic activity, with a greater degree in snc1, while a lesser in nahG, as indicated by the changes of several key photosynthetic parameters. We comprehensively analyzed the expression profiles of photosynthesis-related genes, and observed a positive correlation between Cd tolerance and gene expression levels, wherein the transcription levels of two electron transport-related genes and two amylase-encoding genes were all up-regulated in nahG plants after Cd treatment, implying a significance of the related processes in this genotype against Cd stress.

Map-Based Cloning and Functional Analysis of YE1 in Rice, Which Is Involved in Light-Dependent Chlorophyll Biogenesis and Photoperiodic Flowering Pathway

Light is one of the most important environmental factors that affect many aspects of plant growth, including chlorophyll (Chl) synthesis and flowering time. Here, we identified a rice mutant, yellow leaf and early flowering (ye1), and characterized the gene YE1 by using a map-based cloning method. YE1 encodes a heme oxygenase, which is localized to the chloroplasts. YE1 is expressed in various green tissues, especially in leaves, with a diurnal-rhythmic expression pattern, and its transcripts is also induced by light during leaf-greening. The mutant displays decreased Chl contents with less and disorderly thylakoid lamellar layers in chloroplasts, which reduced the photosynthesis rate. The early flowering phenotype of ye1 was not photoperiod-sensitive. Furthermore, the expression levels of Chl biosynthetic genes were downregulated in ye1 seedlings during de-etiolation responses to light. We also found that rhythmic expression patterns of genes involved in photoperiodic flowering were altered in the mutant. Based on these results, we infer that YE1 plays an important role in light-dependent Chl biogenesis as well as photoperiodic flowering pathway in rice.

Anthocyanin Degrading and Chlorophyll Accumulation Lead to the Formation of Bicolor Leaf in Ornamental Kale

Ornamental kale is a popular decorative plant. We identified a peculiar bicolor leaf double haploid line, with green margins and red centers. The development of bicolor leaves can be divided into three stages: S1, S2, and S3. To probe the reason for bicolor formation, we analyzed the anthocyanin and chlorophyll contents, detected the changes in indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellin 3 (GA3), sugar, and starch contents, and identified the differentially expressed genes (DEGs) using RNA-seq. Results showed that the bicolor leaf phenotype is gradually formed with anthocyanin degrading and chlorophyll accumulation. Anthocyanin content is lower in the green margin (S3_S) than in the red center (S3_C) part at S3. IAA content was positively correlated with anthocyanin content during the bicolor leaf development. During anthocyanin degrading from S1 to S2, cinnamate-4-hydroxylase (C4H) and transport inhibitor response 1 (TIR1) were downregulated, while lateral organ boundaries domain 39 (LBD39) was upregulated. Two peroxidases, two β-glucosidases (BGLU), LBD39, LBD37, detoxifying efflux carrier 35 (DTX35), three no apical meristem (NAC) transcription factors (TFs), and 15 WRKY DNA-binding protein (WRKY) TFs were downregulated in S3_S vs. S3_C. The bicolor phenotype was mainly linked to anthocyanin degrading and chlorophyll accumulation, and that anthocyanin degrading resulted from reduced anthocyanin biosynthesis and increased anthocyanin degradation.

Effects of δ-aminolevulinic acid dehydratase silencing on the primary and secondary metabolisms of citrus

δ-aminolevulinic acid dehydratase (ALAD) is an important enzyme in tetrapyrrole synthesis. ALAD combines two δ-aminolevulinic acid (δ-ALA) molecules to form the pyrrole molecule, porphobilinogen, an important precursor for plant pigments involved in photosynthesis, respiration, and nutrient uptake. In this study, we investigated the effects of silencing of ALAD gene on citrus leaf pigments and metabolites. The ALAD enzyme was inhibited using virus-induced gene silencing (VIGS) technology using citrus tristeza virus (CTV). δ-ALA accumulated in citrus plants inoculated with the recombinant virus (CTV-tALAD) to silence ALAD and resulted in discrete yellow spots (yellow islands) and necrosis in leaves and stems. The levels of chlorophylls, starch, sucrose, trans- and cis-violaxanthin, and α- and β-cryptoxanthin were reduced in CTV-tALAD plants, whereas zeaxanthin was increased. The increase in zeaxanthin and the decrease in its precursors indicated that the reduction in chlorophylls resulted in light damage. Salicylic acid and jasmonic acid levels, as well as emission of (E)-α-bergamotene and (E)-β-farnesene, increased in CTV-tALAD plants indicating these plants were under stress. Our results showed that silencing of ALAD induces stress in plants and that VIGS using mild CTV strains is a promising technique to study biological function of citrus genes.

Molecular and Ultrastructural Mechanisms Underlying Yellow Dwarf Symptom Formation in Wheat after Infection of Barley Yellow Dwarf Virus

Wheat (Tritium aestivum L.) production is essential for global food security. Infection of barley yellow dwarf virus-GAV (BYDV-GAV) results in wheat showing leaf yellowing and plant dwarfism symptom. To explore the molecular and ultrastructural mechanisms underlying yellow dwarf symptom formation in BYDV-GAV-infected wheat, we investigated the chloroplast ultrastructure via transmission electron microscopy (TEM), examined the contents of the virus, H₂O₂, and chlorophyll in Zhong8601, and studied the comparative transcriptome through microarray analyses in the susceptible wheat line Zhong8601 after virus infection. TEM images indicated that chloroplasts in BYDV-GAV-infected Zhong8601 leaf cells were fragmentized. Where thylakoids were not well developed, starch granules and plastoglobules were rare. Compared with mock-inoculated Zhong8601, chlorophyll content was markedly reduced, but the virus and H₂O₂ contents were significantly higher in BYDV-GAV-infected Zhong8601. The transcriptomic analyses revealed that chlorophyll biosynthesis and chloroplast related transcripts, encoding chlorophyll a/b binding protein, glucose-6-phosphate/phosphate translocator 2, and glutamyl-tRNA reductase 1, were down-regulated in BYDV-GAV-infected Zhong8601. Some phytohormone signaling-related transcripts, including abscisic acid (ABA) signaling factors (phospholipase D alpha 1 and calcineurin B-like protein 9) and nine ethylene response factors, were up-regulated. Additionally, reactive oxygen species (ROS)-related genes were transcriptionally regulated in BYDV-GAV infected Zhong8601, including three up-regulated transcripts encoding germin-like proteins (promoting ROS accumulation) and four down-regulated transcripts encoding peroxides (scavenging ROS). These results clearly suggest that the yellow dwarf symptom formation is mainly attributed to reduced chlorophyll content and fragmentized chloroplasts caused by down-regulation of the chlorophyll and chloroplast biosynthesis related genes, ROS excessive accumulation, and precisely transcriptional regulation of the above-mentioned ABA and ethylene signaling- and ROS-related genes in susceptible wheat infected by BYDV-GAV.

Effects of different growth temperatures on growth, development, and plastid pigments metabolism of tobacco (Nicotiana tabacum L.) plants

BACKGROUND

Temperature remarkably affects the growth and metabolism of plants. Tobacco is an important cash crop, and the long-term effects of different growth temperatures (18.5, 23.5 and 28.5 °C, daily average) on growth, development and plastid pigments metabolism of tobacco plants were investigated in this study.

RESULTS

Compared with tobacco plants grown under 23.5 °C, treatments with 18.5 and 28.5 °C inhibited the expansion of leaves. The contents of superoxide anion (O 2·- ), hydrogen peroxide (H2O2) and malonaldehyde (MDA) in the leaves were significantly increased under 28.5 °C from 0 to 60 days, which in turn accelerated the flowering and senescence of tobacco plants. By contrast, the treatment with 18.5 °C remarkably decreased O 2.- , H2O2 and MDA, and delayed the flowering and senescence. Furthermore, treatment with 18.5 °C significantly up-regulated the expression of glutamyl-tRNA reductase (Glu-TR) and magnesium chelatase (MgCH), and down-regulated the ferri chelatase (FeCH), protochlorophyllide oxidoreductase, chlorophyllase (CHLase), phaeophorbide a monooxygenase (PaO) and phytoene synthase (PSY), which further promoted the accumulation of chlorophyll (Chls) and reduced the carotenoids (Cars) in leaves. On the contrary, exposing to 28.5 °C remarkably down-regulated the Glu-TR and MgCH, and up-regulated the FeCH, CHLase, PaO and PSY, which in turn decreased the Chls and increased the Cars in tobacco leaves.

CONCLUSION

As compared with the plants grown under 23.5 °C, lower (18.5 °C) and higher (28.5 °C) growth temperature inhibited the growth of tobacco plants. In general, treatment with 28.5 °C accelerated the flowering and senescence of tobacco plants by enhancing the accumulation of O 2.- and H2O2 in leaves, while exposing to 18.5 °C had the opposite effects. Treatment with 18.5 °C increased the content of Chls and reduced the Cars in leaves. In contrast, Treatment with 28.5 °C decreased the Chls and increased the Cars. Moreover, both O 2.- and H2O2 took part in the breakdown of Chls in tobacco leaves to some extent. The results suggest that growth temperature could regulate growth, development, and plastid pigments metabolism, and 23.5 °C could be an optimal temperature for growth, development and metabolism of plastid pigments of tobacco plants under the experimental conditions.

Gene mapping and transcriptome profiling of a practical photo-thermo-sensitive rice male sterile line with seedling-specific green-revertible albino leaf

Abnormal environment weather can cause rice photoperiod-thermo-sensitive genic male sterile (PTGMS) lines fertile or partially fertile and thus cause the mixture of true hybrids with selfing seeds. Seedling-specific green-revertible albino leaf color mutant can be used to distinguish the real hybrids. Besides, it can also be used as an ideal material to research the development of chloroplast and biosynthesis of chlorophyll. The phenotype of leaf color mutants includes light green, yellowing, albino, green-revertible albino. Gene mutations affecting the synthesis and degradation of photosynthetic pigments, lycopene and heme, the differentiation and development of chloroplast, gibberellins (GAs) biosynthesis, can change the leaf color. We have created a PTGMS line with seedling-specific green-revertible albino leaf named W01S. The leaf phenotype, pollen sterility and fertility, agronomic traits, heredity, gene mapping and RNA-Seq of the differentially expressed genes between albino and green-revertible leaves were investigated. The results showed that W01S is a practical PTGMS line as Pei'ai 64S. The mutation of candidate gene Os03g0594100 (ent-isokaurene C2-hydroxylase-like) in W01S can be related to the biosynthesis of GAs, indole acetic acids, ethylene.

The interactions of algae-bacteria symbiotic system and its effects on nutrients removal from synthetic wastewater

The ability of Chlorella vulgaris-Bacillus licheniformis and Microcystis aeruginosa-Bacillus licheniformis consortiums to eliminate total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and soluble chemical oxygen demand (sCOD) from synthetic wastewater was studied. The highest values of dry cell weight, chlorophyll-a, and chlorophyll metabolism related genes/bacterial rRNA gene copies were obtained in the Chlorella vulgaris-Bacillus licheniformis system at Chlorella vulgaris and Bacillus licheniformis ratio of 1:3. On the 10th day, the Chlorella vulgaris-Bacillus licheniformis system at this ratio removed 86.55%, 80.28% and 88.95% of sCOD, TDP and TDN, respectively. But, the Microcystis aeruginosa-Bacillus licheniformis system at this ratio only removed 65.62%, 70.82%, and 21.56% of sCOD, TDP and TDN, respectively. Chlorella vulgaris and Bacillus licheniformis could coexist as an algae-bacteria consortia and quorum sensing substances (autoinducing peptides and bis (3'-5') diguanylic acid) concentrations were measured. Finally, the interactions and communication patterns between Chlorella vulgaris and Bacillus licheniformis were depicted.

Cytological, physiological, and transcriptomic analyses of golden leaf coloration in Ginkgo biloba L

Ginkgo biloba is grown worldwide as an ornamental plant for its golden leaf color. However, the regulatory mechanism of leaf coloration in G. biloba remains unclear. Here, we compared G. biloba gold-colored mutant leaves and normal green leaves in cytological, physiological and transcriptomic terms. We found that chloroplasts of the mutant were fewer and smaller, and exhibited ruptured thylakoid membranes, indistinct stromal lamellae and irregularly arranged vesicles. Physiological experiments also showed that the mutant had a lower chlorophyll, lower flavonoid and higher carotenoid contents (especially lutein). We further used transcriptomic sequencing to identify 116 differentially expressed genes (DEGs) and 46 transcription factors (TFs) involved in chloroplast development, chlorophyll metabolism, pigment biosynthesis and photosynthesis. Among these, the chlorophyll biosynthesis-related PPO showed down-regulation, while chlorophyll degradation-related NYC/NOL had up-regulated expression in mutant leaves. Z-ISO, ZDS, and LCYE, which are involved in carotenoid biosynthesis were up-regulated. Quantitative real-time PCR (RT-qPCR) further confirmed the altered expression levels of these genes at three stages. The alteration of PPO and NYC/NOL gene expression might affect chlorophyll biosynthesis and promote degradation of chlorophyll b to chlorophyll a, while the up-regulated genes Z-ISO, ZDS and LCYE enhanced carotenoid accumulation. Consequently, changes in the ratio of carotenoids to chlorophylls were the main factors driving the golden leaf coloration in the mutant G. biloba.

Molecular Profiling of Pierce's Disease Outlines the Response Circuitry of Vitis vinifera to Xylella fastidiosa Infection

Pierce's disease is a major threat to grapevines caused by the bacterium Xylella fastidiosa. Although devoid of a type 3 secretion system commonly employed by bacterial pathogens to deliver effectors inside host cells, this pathogen is able to influence host parenchymal cells from the xylem lumen by secreting a battery of hydrolytic enzymes. Defining the cellular and biochemical changes induced during disease can foster the development of novel therapeutic strategies aimed at reducing the pathogen fitness and increasing plant health. To this end, we investigated the transcriptional, proteomic, and metabolomic responses of diseased Vitis vinifera compared to healthy plants. We found that several antioxidant strategies were induced, including the accumulation of gamma-aminobutyric acid (GABA) and polyamine metabolism, as well as iron and copper chelation, but these were insufficient to protect the plant from chronic oxidative stress and disease symptom development. Notable upregulation of phytoalexins, pathogenesis-related proteins, and various aromatic acid metabolites was part of the host responses observed. Moreover, upregulation of various cell wall modification enzymes followed the proliferation of the pathogen within xylem vessels, consistent with the intensive thickening of vessels' secondary walls observed by magnetic resonance imaging. By interpreting the molecular profile changes taking place in symptomatic tissues, we report a set of molecular markers that can be further explored to aid in disease detection, breeding for resistance, and developing therapeutics.

5-Aminolevulinic Acid (ALA) Alleviated Salinity Stress in Cucumber Seedlings by Enhancing Chlorophyll Synthesis Pathway

5-Aminolevulinic acid (ALA) is a common precursor of tetrapyrroles as well as a crucial growth regulator in higher plants. ALA has been proven to be effective in improving photosynthesis and alleviating the adverse effects of various abiotic stresses in higher plants. However, little is known about the mechanism of ALA in ameliorating the photosynthesis of plant under abiotic stress. In this paper, we studied the effects of exogenous ALA on salinity-induced damages of photosynthesis in cucumber (Cucumis sativus L.) seedlings. We found that the morphology (plant height, leave area), light utilization capacity of PS II [qL, Y(II)] and gas exchange capacity (Pn, gs, Ci, and Tr) were significantly retarded under NaCl stress, but these parameters were all recovered by the foliar application of 25 mg L^-1 ALA. Besides, salinity caused heme accumulation and up-regulation of gene expression of ferrochelatase (HEMH) with suppression of other genes involved in chlorophyll synthesis pathway. Exogenously application of ALA under salinity down-regulated the heme content and HEMH expression, but increased the gene expression levels of glutamyl-tRNA reductase (HEMA1), Mg-chelatase (CHLH), and protochlorophyllide oxidoreductase (POR). Moreover, the contents of intermediates involved in chlorophyll branch were increased by ALA, including protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX, protochlorophyllide (Pchlide), and chlorophyll (Chl a and Chl b) under salt stress. Ultrastructural observation of mesophyll cell showed that the damages of photosynthetic apparatus under salinity were fixed by ALA. Collectively, the chlorophyll biosynthesis pathway was enhanced by exogenous ALA to improve the tolerance of cucumber under salinity.

Proteome and Acetyl-Proteome Profiling of Camellia sinensis cv. 'Anjin Baicha' during Periodic Albinism Reveals Alterations in Photosynthetic and Secondary Metabolite Biosynthetic Pathways

Tea leaf color is not only important from an aesthetics standpoint but is also related to tea quality. To investigate the molecular mechanisms that determine tea leaf color, we examined Camellia sinensis cv. 'Anjin Baicha' (an albino tea cultivar) by tandem mass tag isobaric labeling to generate a high-resolution proteome and acetyl-proteome atlas of three leaf developmental stages. We identified a total of 7,637 proteins and quantified 6,256; of these, 3,232 were classified as differentially accumulated proteins (DAPs). We also identified 3,161 lysine acetylation sites in 1,752 proteins and quantified 2,869 in 1,612 proteins. The acetylation levels at 468 sites were significantly altered across the three developmental stages during periodic albinism; the corresponding proteins were associated with a variety of biological processes. Interestingly, a large number of DAPs and acetylated proteins with increased/decreased acetylation were related to photosynthesis and secondary metabolite biosynthetic pathways, suggesting that the accumulation or acetylation level of these proteins regulates periodic albinism in 'Anjin Baicha.' Additionally, overlap between succinylome and acetylome among three 'Anjin Baicha' developmental stages were found. These data provide important insight into the mechanisms of leaf coloration in the tea plant. The mass spectrometry data have been deposited to Proteome X change via the PRIDE partner repository with the data set identifier PXD008134.

5-Aminolevulinic Acid Dehydratase Gene Dosage Affects Programmed Cell Death and Immunity

Programmed cell death (PCD) is an important form to protect plants from pathogen attack. However, plants must precisely control the PCD process under microbe attacks to avoid detrimental effects. The complexity of how plants balance the defense activation and PCD requires further clarification. Lesion mimic mutants constitute an excellent material to study the crosstalk between them. Here, we identified a Gossypium hirsutum (cotton) lesion mimic mutant (Ghlmm), which exhibits necrotic leaf damage and enhanced disease resistance. Map-based cloning demonstrated that GhLMMD, encoding 5-aminolevulinic acid dehydratase and located on chromosome D5, was responsible for the phenotype. The mutant was resulted from a nonsense mutation within the coding region of GhLMMD It exhibited an overaccumulation of the 5-aminolevulinic acid, elevated levels of reactive oxygen species and salicylic acid, along with constitutive expression of pathogenesis-related genes and enhanced resistance to the Verticillium dahliae infection. Interestingly, GhLMM plays a dosage-dependent role in regulating PCD of cotton leaves and resistance to V. dahliae infection. This study provides a new strategy on the modulation of plant immunity, particularly in polyploidy plants.

Quantitative Succinyl-Proteome Profiling of Camellia sinensis cv. 'Anji Baicha' During Periodic Albinism

Lysine succinylation is a novel dynamic and evolutionarily conserved post-translational modification (PTM) that regulates various biological processes. ‘Anji Baicha’ is an albino tea variety that exhibits temperature-based variability of leaf colour and amino acid concentrations. However, the mechanism underlying albinism in ‘Anji Baicha’ has not been investigated at the level of succinylation. Here, we identify 3530 lysine succinylation sites mapped to 2132 proteins in ‘Anji Baicha’, representing the first extensive data on the lysine succinylome in the tea plant. Eleven conserved succinylation motifs were enriched among the identified succinylated peptides. The protein-protein interaction maps were visualized using Cytoscape software. Comparison across three typical developmental stages of ‘Anji Baicha’ revealed that proteins exhibiting differential succinylation levels were primarily involved in photosynthesis, carbon fixation, biosynthesis of amino acids and porphyrin and chlorophyll metabolism, suggesting that these succinylated proteins are involved in ‘Anji Baicha’ leaf colour variability. These results not only deepen our understanding of the mechanism underlying ‘Anji Baicha’ albinism and the regulatory role of succinylation in the tea plant but also provide new insight into molecular breeding for leaf colour variety.

Identification of a peroxisomal-targeted aldolase involved in chlorophyll biosynthesis and sugar metabolism in rice

Chlorophyll plays remarkable and critical roles in photosynthetic light-harvesting, energy transduction and plant development. In this study, we identified a rice Chl-deficient mutant, ygdl-1 (yellow green and droopy leaf-1), which showed yellow-green leaves throughout plant development with decreased content of Chls and carotene and an increased Chl a/b ratio. The ygdl-1 mutant also exhibited severe defects in chloroplast development, including disorganized grana stacks. Sequence analysis revealed that the mutant contained a T-DNA insertion within the promoter of a fructose-1,6-bisphosphate aldolase (OsAld-Y), which dramatically reduced the OsAld-Y mRNA level, and its identity was verified by transgenic complementation. Real-time PCR analysis showed that the expression levels of genes associated with chlorophyll biosynthesis and chloroplast development were concurrently altered in the ygdl-1 mutant. The expression of OsAld-Y-GFP fusion protein in tobacco epidermal cells showed that OsAld-Y was localized to the peroxisome. In addition, the analysis of primary carbon metabolites revealed the significantly reduced levels of sucrose and fructose in the mutant leaves, while the glucose content was similar to wild-type plants. Our results suggest that the OsAld-Y participates in Chl accumulation, chloroplast development and plant growth by influencing the photosynthetic rate of leaves and the sugar metabolism of rice.