The apple BTB protein MdBT2 positively regulates MdCOP1 abundance to repress anthocyanin biosynthesis

Orchestrating anthocyanin biosynthesis in fruit of fruit trees: Transcriptional, post-transcriptional, and post-translational regulation

Coloration is an important appearance quality that contributes to product value. Anthocyanins, a type of flavonoid, not only impart rich plants color, but also contribute to human health because of their antioxidant properties, such as preventing cardiovascular disease and reducing obesity. This benefit mainly stems from various fruits. Accordingly, based on the consumption demand of beauty and nutrition, the creation of fruit tree products rich in anthocyanin is becoming an important breeding goal. The synthesis of anthocyanin has been investigated in various fruits, which is modulated by a variety of endogenous and exogenous factors, including transcription factors (TFs), plant hormones, and environmental factors (such as light, low temperature, drought). However, the detailed mechanisms in fruits of fruit trees have not been thoroughly elucidated. This review comprehensively examines the regulation of anthocyanin biosynthesis at the transcriptional, post-transcriptional, and post-translational levels, which is important for the application of molecular design strategies to cultivate high-quality fruits. At the transcriptional level, TFs were summarized to directly regulate anthocyanin biosynthesis genes, target non-anthocyanin biosynthesis pathway genes, interact with other proteins to mediate anthocyanin synthesis, and regulate anthocyanin synthesis by environmental factors and plant hormones. At the post-transcriptional level, non-coding RNAs (ncRNAs) were elucidated to mediate anthocyanin synthesis. At the post-translational level, a variety of post-translational modifications, including phosphorylation, ubiquitination, sumoylation, and persulfidation, have been elucidated to exhibit crucial functions in anthocyanin biosynthesis.

Genome-Wide Identification of the BTB Domain-Containing Protein Gene Family in Pepper (Capsicum annuum L.)

Pepper (Capsicum annuum L.), recognized as a globally preeminent vegetable, holds substantial economic and nutritional value. The BTB (broad-complex, tramtrack, and bric-a-brac) family of proteins, characterized by a highly conserved BTB domain, also denoted as the POZ domain, are intricately involved in a diverse array of biological processes. However, the existing corpus of research regarding pepper BTB genes remains relatively meager. In this study, a total of 72 CaBTB gene members were meticulously identified from the entire genome of pepper. Phylogenetic analysis illuminated the presence of conspicuous collinear relationships between the CaBTB genes and those of its closely affiliated species. Gene expression profiling and RT-qPCR analysis revealed that multiple CaBTB genes exhibited pronounced differential expression under diverse treatment regimens. Expression pattern analysis unveiled that CaBTB25 manifested a remarkably elevated abundance in leaves. Moreover, its promoters were replete with an abundance of light-responsive cis-elements. Our comprehensive and in-depth explorations into subcellular localization revealed that CaBTB25 was predominantly detected to localize within the nucleus and lacked transcriptional activation. This research provides a crucial theoretical edifice, enabling a more profound understanding of the biological functions of the BTB gene family in pepper, thereby underscoring its potential significance within the intricate network of gene-environment interactions.

Light regulates SlCOP1-mediated degradation of SlJAF13, a transcription factor essential for anthocyanin biosynthesis in Aft tomato fruit

When they are exposed to light, the fruit of tomato plants (Solanum lycopersicum) carrying the dominant gene Anthocyanin fruit (Aft) accumulate anthocyanins. As the regulatory mechanism underlying this accumulation remains unclear, the role played by light in the regulation of SlJAF13, a bHLH transcription factor responsible for anthocyanin biosynthesis in tomato fruit peel, was examined. Gene expression analysis, GUS staining, and immunoblotting assays revealed that light enhanced the stability of SlJAF13 protein at a post-transcriptional level rather than transcriptionally. Protein-protein interaction assays and in vitro ubiquitination analysis revealed that CONSTITUTIVE PHOTOMORPHOGENIC1 (SlCOP1), a RING E3 ubiquitin ligase, physically interacted with SlJAF13, resulting in the ubiquitination and subsequent degradation of SlJAF13. Additionally, reductions in the levels of both anthocyanins and SlJAF13 protein were observed in fruit from plants over-expressing SlCOP1, providing further evidence that the suppressive effect of SlCOP1 on anthocyanin accumulation facilitated SlJAF13 degradation. These findings confirm the role of light in the stabilization of SIJAF13 in tomato fruit and thus provide novel insight into anthocyanin regulation in an important horticultural crop species under light conditions.

SmCSN5 is a synergist in the transcription factor SmMYB36-mediated biosynthesis of tanshinones and phenolic acids in Salvia miltiorrhiza

The ubiquitin-26S proteasome system (UPS) is associated with protein stability and activity, regulation of hormone signaling, and the production of secondary metabolites in plants. Though the mechanism of action of SmMYB36 on the tanshinone and phenolic acid biosynthesis is well understood, its regulation through post-translational modifications is unclear. A constitutive photomorphogenesis 9 (COP9) signalosome subunit 5 (SmCSN5), which interacted with SmMYB36 and inhibited its ubiquitination-based degradation, was identified in Salvia miltiorrhiza. SmCSN5 promoted tanshinone biosynthesis but inhibited phenolic acid biosynthesis in the hairy roots of S. miltiorrhiza. SmMYB36 also activated the transcription of the target genes SmDXS2 and SmCPS1 but repressed that of SmRAS in a SmCSN5-dependent manner. SmCSN5 acts as a positive regulator in MeJA-induced biosynthesis of tanshinones and phenolic acids. Specifically, SmCSN5 alone, when expressed transiently in tobacco and rice protoplasts, was localized to the cytoplasm, cell membrane, and nucleus, whereas when coexpressed with SmMYB36, it was detected only in the nucleus. Additionally, the degradation of SmMYB361-153 by ubiquitination was lowered after truncation of the self-activating structural domain of SmMYB36154-160. Collectively, these results suggest that SmCSN5 affected the transcriptional activation of SmMYB36 and stabilized SmMYB36, providing insights into the SmMYB36-based regulation of the accumulation of tanshinone and phenolic acid at the transcriptional and post-translational levels.

MdHMGB15-MdXERICO-MdNRP module mediates salt tolerance of apple by regulating the expression of salt stress-related genes

INTRODUCTION

Soil salinity is an important limiting factor for plant growth. As a RING-type E3 ubiquitin ligase, MdXERICO is highly responsive to salt stress and can enhance the salt tolerance of plants. However, the molecular mechanism for the response of MdXERICO to salt stress remains unclear.

OBJECTIVES

This study aims to dissect the molecular mechanisms for MdXERICO to regulate plant response to salt stress.

METHODS

Transcriptome data were compared to obtain the salt stress-induced gene MdXERICO. Transgenic apple seedlings, apple calli, Arabidopsis, and tomato material were obtained using Agrobacterium-mediated transformation assays. Semiendogenous co-immunoprecipitation analysis, yeast two-hybrid, pull-down and dual-luciferase reporter system were used to detect the protein-protein interactions. Electrophoretic mobility shift assay, yeast one-hybrids, dual luciferase and Gus staining assay were employed to verify the protein-DNA interactions.

RESULTS

The results revealed that MdXERICO interacted with MdNRP and improved salt tolerance of apple by ubiquitinating and degrading MdNRP via the 26S proteasome pathway. Moreover, the HMG box-containing transcription factor MdHMGB15 interacted with the MdXERICO promoter, thereby activating its expression and enhancing the salt tolerance of apple.

CONCLUSION

This study explores the apple's tolerance to salt stress through the MdHMGB15-MdXERICO-MdNRP module, and provides potential targets for engineering salt-tolerant varieties.

PKS1 involved in anthocyanin accumulation in red-skinned pear fruit

KEY MESSAGE

PcPKS1 can prevent PcCSN5a from acting as an inhibitor of anthocyanin synthesis by binding to PcCSN5a, ultimately leading the accumulation of anthocyanins. Light is a crucial environmental factor that regulates anthocyanin accumulation in plants. However, the molecular mechanisms by which light signals influence anthocyanin accumulation in fruits have not yet been fully elucidated. We identified the differentially expressed gene Pyrus communis PHYTOCHROME KINASE SUBSTRATE 1 (PcPKS1), which is associated with anthocyanin accumulation in plants, in a previous study. Through measurements of the expression of PcPKS1 in 'Starkrimson' and 'Red Bartlett' pear fruit at various developmental stages and in different pear varieties, quantitative and transient expression experiments conducted on red and green skin tissues confirmed the relationship between PcPKS1 and anthocyanin accumulation. Pyrus communis COP9 SIGNALOSOME COMPLEX SUBUNIT 5A (PcCSN5a) protein, which interacts with PcPKS1, was identified from a yeast library screening. The interaction between the two proteins was validated through yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and split-luciferase (Split-LUC) experiments. Subcellular localization and co-localization experiments revealed that PcPKS1 was localized to the cell membrane, whereas PcCSN5a was localized to the cell membrane and nucleus, with PcPKS1 and PcCSN5a co-localized on the cell membrane. Transient expression in strawberry fruit indicated that PcPKS1 positively regulated anthocyanin accumulation, whereas PcCSN5a negatively regulated anthocyanin accumulation and diminished the capacity of PcPKS1 to promote anthocyanin accumulation. This study provides novel insights into the molecular mechanisms underlying light-regulated anthocyanin accumulation in red-skinned pear fruit.

Plant U-box E3 ligase PpPUB59 regulates anthocyanin accumulation by ubiquitinating PpBBX24 in 'Zaosu' pear and its red bud mutation

Ubiquitination is the specific modification of target proteins in cells by ubiquitin molecules, which is under the action of a series of special enzymes such as ubiquitin-activating enzymes, binding, and ligase enzymes. Ubiquitination plays an essential role in anthocyanin accumulation in plants. There are few studies on the coloring of pear peel by ubiquitin ligase E3. In this study, an E3 ubiquitin ligase protein PpPUB59 with seven WD40 repeats was cloned. And the function of PpPUB59 on the ubiquitination and protein stability of PpBBX24 and Ppbbx24-del, and the possible action mechanism in the anthocyanin accumulation of 'Red Zaosu' was studied. Our results showed that the WD40 repeats were verified to be the key domain interacting with the VP domain of BBX protein. PpPUB59 could degrade PpBBX24 in vitro by interacting with the VP domain but could not degrade the mutant PpBBX24-del without the VP domain. Dual luciferase assay showed that Ppbbx24-del could activate the PpCHS promoter, while PpPUB59 did not interfere with this activation; PpBBX24 could not activate the promotor of PpCHS but could suppress the activation of PpHY5; when the PpPUB59 was co-expressed with PpBBX24 and PpHY5, the activation roles of PpHY5 in the promotor of PpCHS was not recovered. BiFC and yeast two-hybrid experiments showed that PpPUB59 could also interact with PpHY5, which may make it ubiquitinated and degraded by 26S proteasome. In conclusion, PpPUB59 played an essential role in pear anthocyanin accumulation by ubiquitinating the associated transcription factors. These findings clarified the mutant mechanism of the 'Red Zaosu' pear at the post-translational modification level and enriched the regulation theory of the pear anthocyanin accumulation.

CsCPC, an R3-MYB transcription factor, acts as a negative regulator of citric acid accumulation in Citrus

The citric acid accumulation during fruit ripening determines the quality of fleshy fruits. However, the molecular mechanism underlying citric acid accumulation is not clearly understood yet in citrus due to the scarcity of paired germplasm that exhibits significant difference in organic acid accumulation. Two citrus triploid hybrids with distinct citric acid content in their mature fruits were herein identified from a previously conducted interploidy cross in our group, providing an ideal paired material for studying acid accumulation in citrus. Through a comparative transcriptome analysis of the pulps of the above two triploid hybrids, an R3-MYB transcription factor, CAPRICE (CsCPC), was identified to be a regulator of citric acid accumulation in citrus fruits. Through transgenic experiments involving overexpression (in callus and kumquat fruits) and RNAi (in lemon leaves), we demonstrated that CsCPC suppresses citric acid accumulation by negatively regulating the expression of CsPH1 and CsPH5. Moreover, CsCPC competed with an R2R3-MYB CsPH4 for binding to ANTHOCYANIN1 (CsAN1) and thus disturbed the activation of CsPH1 and CsPH5 that encode vacuolar P-ATPase, which eventually led to a decrease in citric acid content. CsPH4 activated the expression of CsCPC and thus formed an activator-repressor feedback loop, which ultimately inhibited citric acid accumulation in citrus fruit. In summary, this study reveals a new regulatory mechanism of CsCPC-mediated inhibition of citric acid accumulation in citrus fruits, which would support the improvement of citrus fruit quality.

MsMYB62-like as a negative regulator of anthocyanin biosynthesis in Malus spectabilis

Crabapple is a valuable tree species in gardens due to its captivating array of flower and leaf colors, rendering it a favored choice in landscaping. The economic and ornamental values of Malus crabapple are closely associated with the biosynthesis of anthocyanin, a pigment responsible for its vibrant hues. The intricate regulation of anthocyanin biosynthesis involves the concerted activity of various genes. However, the specific mechanism governing this process in crabapple warrants in-depth exploration. In this study, we explored the inhibitory role of MsMYB62-like in anthocyanin biosynthesis. We identified MsDFR and MsANS as two downstream target genes of MsMYB62-like. These genes encode enzymes integral to the anthocyanin biosynthetic pathway. The findings demonstrate that MsMYB62-like directly binds to the promoters of MsDFR and MsANS, resulting in the downregulation of their expression levels. Additionally, our observations indicate that the plant hormone cytokinins exert a suppressive effect on the expression levels of MsMYB62-like, while concurrently upregulating MsDFR and MsANS. This study reveals that the MsMYB62-like-MsDFR/MsANS module plays an important role in governing anthocyanin levels in Malus crabapple. Notably, the regulatory interplay is modulated by the plant hormone cytokinins.

Ubiquitin ligase VvPUB26 in grapevine promotes proanthocyanidin synthesis and resistance to powdery mildew

Proanthocyanidins (PAs) are an important group of flavonoids that contribute to astringency, color, and flavor in grapes (Vitis vinifera) and wines. They also play a crucial role in enhancing plant resistance to various stresses. However, the underlying regulatory mechanism governing PAs biosynthesis, particularly in relation to conferring resistance to powdery mildew, has not been extensively explored. This study focused on identifying a key player in PAs biosynthesis, namely the plant U-box (PUB) E3 ubiquitin ligase VvPUB26. We discovered that overexpression of VvPUB26 in grapes leads to a significant increase in PAs content, whereas interfering with VvPUB26 has the opposite effect. Additionally, our findings demonstrated that overexpression of VvPUB26 in transgenic grapevines enhances defense against powdery mildew while interfering with VvPUB26 results in increased susceptibility to the pathogen. Interestingly, we observed that VvPUB26 interacts with the WRKY transcription factor VvWRKY24, thereby facilitating ubiquitination and degradation processes. Through RNA-Seq analysis, we found that VvWRKY24 primarily participates in secondary metabolites biosynthesis, metabolic pathways, and plant-pathogen interaction. Notably, VvWRKY24 directly interacts with the promoters of dihydroflavonol-4-reductase (DFR) and leucoanthocyanidin reductase (LAR) to inhibit PAs biosynthesis. Meanwhile, VvWRKY24 also influences the expression of MYB transcription factor genes related to PAs synthesis. In conclusion, our results unveil a regulatory module involving VvPUB26-VvWRKY24-VvDFR/VvLAR that plays a fundamental role in governing PAs biosynthesis in grapevines. These findings enhance our understanding of the relationship between PAs biosynthesis and defense mechanisms against powdery mildew.

Calmodulin-like protein MdCML15 interacts with MdBT2 to modulate iron homeostasis in apple

BTB and TAZ domain proteins (BTs) function as specialized adaptors facilitating substrate recognition of the CUL3-RING ubiquitin ligase (CRL3) complex that targets proteins for ubiquitination in reaction to diverse pressures. Nonetheless, knowledge of the molecular mechanisms by which the apple scaffold protein MdBT2 responds to external and internal signals is limited. Here we demonstrate that a putative Ca 2+ sensor, calmodulin-like 15 (MdCML15), acts as an upstream regulator of MdBT2 to negatively modulate its functions in plasma membrane H+-ATPase regulation and iron deficiency tolerance. MdCML15 was identified to be substantially linked to MdBT2, and to result in the ubiquitination and degradation of the MdBT2 target protein MdbHLH104. Consequently, MdCML15 repressed the MdbHLH104 target, MdAHA8's expression, reducing levels of a specific membrane H+-ATPase. Finally, the phenotype of transgenic apple plantlets and calli demonstrated that MdCML15 modulates membrane H+-ATPase-produced rhizosphere pH lowering alongside iron homeostasis through an MdCML15-MdBT2-MdbHLH104-MdAHA8 pathway. Our results provide new insights into the relationship between Ca2+ signaling and iron homeostasis.

The AP2/ERF transcription factor MdDREB2A regulates nitrogen utilisation and sucrose transport under drought stress

Drought stress is one of the main environmental factors limiting plant growth and development. Plants adapt to changing soil moisture by modifying root architecture, inducing stomatal closure, and inhibiting shoot growth. The AP2/ERF transcription factor DREB2A plays a key role in maintaining plant growth in response to drought stress, but the molecular mechanism underlying this process remains to be elucidated. Here, it was found that overexpression of MdDREB2A positively regulated nitrogen utilisation by interacting with DRE cis-elements of the MdNIR1 promoter. Meanwhile, MdDREB2A could also directly bind to the promoter of MdSWEET12, which may enhance root development and nitrogen assimilation, ultimately promoting plant growth. Overall, this regulatory mechanism provides an idea for plants in coordinating with drought tolerance and nitrogen assimilation to maintain optimal plant growth and development under drought stress.

Haplotype-resolved genome assembly of the diploid Rosa chinensis provides insight into the mechanisms underlying key ornamental traits

Roses are consistently ranked at the forefront in cut flower production. Increasing demands of market and changing climate conditions have resulted in the need to further improve the diversity and quality of traits. However, frequent hybridization leads to highly heterozygous nature, including the allelic variants. Therefore, the absence of comprehensive genomic information leads to them making it challenging to molecular breeding. Here, two haplotype-resolved chromosome genomes for Rosa chinensis 'Chilong Hanzhu' (2n = 14) which is high heterozygous diploid old Chinese rose are generated. An amount of genetic variation (1,605,616 SNPs, 209,575 indels) is identified. 13,971 allelic genes show differential expression patterns between two haplotypes. Importantly, these differences hold valuable insights into regulatory mechanisms of traits. RcMYB114b can influence cyanidin-3-glucoside accumulation and the allelic variation in its promoter leads to differences in promoter activity, which as a factor control petal color. Moreover, gene family expansion may contribute to the abundance of terpenes in floral scents. Additionally, RcANT1, RcDA1, RcAG1 and RcSVP1 genes are involved in regulation of petal number and size under heat stress treatment. This study provides a foundation for molecular breeding to improve important characteristics of roses.

E3 ubiquitin ligase MaRZF1 modulates high temperature-induced green ripening of banana by degrading MaSGR1

High temperatures (>24°C) prevent the development of a yellow peel on bananas called green ripening, owing to the inhibition of chlorophyll degradation. This phenomenon greatly reduces the marketability of banana fruit, but the mechanisms underlining high temperature-repressed chlorophyll catabolism need to be elucidated. Herein, we found that the protein accumulation of chlorophyll catabolic enzyme MaSGR1 (STAY-GREEN 1) was reduced when bananas ripened at high temperature. Transiently expressing MaSGR1 in banana peel showed its positive involvement in promoting chlorophyll degradation under high temperature, thereby weakening green ripening phenotype. Using yeast two-hybrid screening, we identified a RING-type E3 ubiquitin ligase, MaRZF1 (RING Zinc Finger 1), as a putative MaSGR1-interacting protein. MaRZF1 interacts with and targets MaSGR1 for ubiquitination and degradation via the proteasome pathway. Moreover, upregulating MaRZF1 inhibited chlorophyll degradation, and attenuated MaSGR1-promoted chlorophyll degradation in bananas during green ripening, indicating that MaRZF1 negatively regulates chlorophyll catabolism via the degradation of MaSGR1. Taken together, MaRZF1 and MaSGR1 form a regulatory module to mediate chlorophyll degradation associated with high temperature-induced green ripening in bananas. Therefore, our findings expand the understanding of posttranslational regulatory mechanisms of temperature stress-caused fruit quality deterioration.

Multi-Omics Analysis Reveals That Anthocyanin Degradation and Phytohormone Changes Regulate Red Color Fading in Rapeseed (Brassica napus L.) Petals

Flower color is an important trait for the ornamental value of colored rapeseed (Brassica napus L.), as the plant is becoming more popular. However, the color fading of red petals of rapeseed is a problem for its utilization. Unfortunately, the mechanism for the process of color fading in rapeseed is unknown. In the current study, a red flower line, Zhehuhong, was used as plant material to analyze the alterations in its morphological and physiological characteristics, including pigment and phytohormone content, 2 d before flowering (T1), at flowering (T2), and 2 d after flowering (T3). Further, metabolomics and transcriptomics analyses were also performed to reveal the molecular regulation of petal fading. The results show that epidermal cells changed from spherical and tightly arranged to totally collapsed from T1 to T3, according to both paraffin section and scanning electron microscope observation. The pH value and all pigment content except flavonoids decreased significantly during petal fading. The anthocyanin content was reduced by 60.3% at T3 compared to T1. The content of three phytohormones, 1-aminocyclopropanecarboxylic acid, melatonin, and salicylic acid, increased significantly by 2.2, 1.1, and 30.3 times, respectively, from T1 to T3. However, auxin, abscisic acid, and jasmonic acid content decreased from T1 to T3. The result of metabolomics analysis shows that the content of six detected anthocyanin components (cyanidin, peonidin, pelargonidin, delphinidin, petunidin, and malvidin) and their derivatives mainly exhibited a decreasing trend, which was in accordance with the trend of decreasing anthocyanin. Transcriptomics analysis showed downregulation of genes involved in flavonol, flavonoid, and anthocyanin biosynthesis. Furthermore, genes regulating anthocyanin biosynthesis were preferentially expressed at early stages, indicating that the degradation of anthocyanin is the main issue during color fading. The corresponding gene-encoding phytohormone biosynthesis and signaling, JASMONATE-ZIM-DOMAIN PROTEIN, was deactivated to repress anthocyanin biosynthesis, resulting in fading petal color. The results clearly suggest that anthocyanin degradation and phytohormone regulation play essential roles in petal color fading in rapeseed, which is a useful insight for the breeding of colored rapeseed.

Whole genome scanning of a Mediterranean basin hotspot collection provides new insights into olive tree biodiversity and biology

Olive tree (Olea europaea L. subsp. europaea var. europaea) is one of the most important species of the Mediterranean region and one of the most ancient species domesticated. The availability of whole genome assemblies and annotations of olive tree cultivars and oleaster (O. europaea subsp. europaea var. sylvestris) has contributed to a better understanding of genetic and genomic differences between olive tree cultivars. However, compared to other plant species there is still a lack of genomic resources for olive tree populations that span the entire Mediterranean region. In the present study we developed the most complete genomic variation map and the most comprehensive catalog/resource of molecular variation to date for 89 olive tree genotypes originating from the entire Mediterranean basin, revealing the genetic diversity of this commercially significant crop tree and explaining the divergence/similarity among different variants. Additionally, the monumental ancient tree 'Throuba Naxos' was studied to characterize the potential origin or routes of olive tree domestication. Several candidate genes known to be associated with key agronomic traits, including olive oil quality and fruit yield, were uncovered by a selective sweep scan to be under selection pressure on all olive tree chromosomes. To further exploit the genomic and phenotypic resources obtained from the current work, genome-wide association analyses were performed for 23 morphological and two agronomic traits. Significant associations were detected for eight traits that provide valuable candidates for fruit tree breeding and for deeper understanding of olive tree biology.

E3 ligase MaNIP1 degradation of NON-YELLOW COLORING1 at high temperature inhibits banana degreening

Banana (Musa acuminata) fruit ripening under high temperatures (>24 °C) undergoes green ripening due to failure of chlorophyll degradation, which greatly reduces marketability. However, the mechanism underlying high temperature-repressed chlorophyll catabolism in banana fruit is not yet well understood. Here, using quantitative proteomic analysis, 375 differentially expressed proteins were identified in normal yellow and green ripening in banana. Among these, one of the key enzymes involved in chlorophyll degradation, NON-YELLOW COLORING 1 (MaNYC1), exhibited reduced protein levels when banana fruit ripened under high temperature. Transient overexpression of MaNYC1 in banana peels resulted in chlorophyll degradation under high temperature, which weakens the green ripening phenotype. Importantly, high temperature induced MaNYC1 protein degradation via the proteasome pathway. A banana RING E3 ligase, NYC1-interacting protein 1 (MaNIP1), was found to interact with and ubiquitinate MaNYC1, leading to its proteasomal degradation. Furthermore, transient overexpression of MaNIP1 attenuated MaNYC1-induced chlorophyll degradation in banana fruits, indicating that MaNIP1 negatively regulates chlorophyll catabolism by affecting MaNYC1 degradation. Taken together, the findings establish a post-translational regulatory module of MaNIP1-MaNYC1 that mediates high temperature-induced green ripening in bananas.

Why do plants blush when they are hungry?

Foliar anthocyanins, as well as other secondary metabolites, accumulate transiently under nutritional stress. A misconception that only nitrogen or phosphorus deficiency induces leaf purpling/reddening has led to overuse of fertilizers that burden the environment. Here, we emphasize that several other nutritional imbalances induce anthocyanin accumulation, and nutrient-specific differences in this response have been reported for some deficiencies. A range of ecophysiological functions have been attributed to anthocyanins. We discuss the proposed functions and signalling pathways that elicit anthocyanin synthesis in nutrient-stressed leaves. Knowledge from the fields of genetics, molecular biology, ecophysiology and plant nutrition is combined to deduce how and why anthocyanins accumulate under nutritional stress. Future research to fully understand the mechanisms and nuances of foliar anthocyanin accumulation in nutrient-stressed crops could be utilized to allow these leaf pigments to act as bioindicators for demand-oriented application of fertilizers. This would benefit the environment, being timely due to the increasing impact of the climate crisis on crop performance.

Multilevel regulation of anthocyanin-promoting R2R3-MYB transcription factors in plants

Anthocyanins are common secondary metabolites in plants that confer red, blue, and purple colorations in plants and are highly desired by consumers for their visual appearance and nutritional quality. In the last two decades, the anthocyanin biosynthetic pathway and transcriptional regulation of anthocyanin biosynthetic genes (ABGs) have been well characterized in many plants. From numerous studies on model plants and horticultural crops, many signaling regulators have been found to control anthocyanin accumulation via regulation of anthocyanin-promoting R2R3-MYB transcription factors (so-called R2R3-MYB activators). The regulatory mechanism of R2R3-MYB activators is mediated by multiple environmental factors (e.g., light, temperature) and internal signals (e.g., sugar, ethylene, and JA) in complicated interactions at multiple levels. Here, we summarize the transcriptional control of R2R3-MYB activators as a result of natural variations in the promoter of their encoding genes, upstream transcription factors and epigenetics, and posttranslational modifications of R2R3-MYB that determine color variations of horticultural plants. In addition, we focus on progress in elucidating the integrated regulatory network of anthocyanin biosynthesis mediated by R2R3-MYB activators in response to multiple signals. We also highlight a few gene cascade modules involved in the regulation of anthocyanin-related R2R3-MYB to provide insights into anthocyanin production in horticultural plants.