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

Physiological, Cytological and Transcriptome Analysis of a Yellow-Green Leaf Mutant in Magnolia sinostellata

Leaf color mutants serve as excellent models for investigating the metabolic pathways involved in chlorophyll biosynthesis, chloroplast development, and photosynthesis in plants. This study aimed to elucidate the mechanisms underlying color formation in the yellow-green leaf mutant (YL) of Magnolia sinostellata by employing physiological, cytological and transcriptomic analyses to compare the mutant with control plants (wild type Magnolia sinostellata, WT). Physiological assessments revealed a reduction in chlorophyll content, particularly chlorophyll b, alongside an increase in the flavonoid level in YL relative to WT. Cytological examinations indicated the presence of defective chloroplasts within the mesophyll cells of the mutants. Transcriptomic analysis identified 8205 differentially expressed genes, with 4159 upregulated and 4046 downregulated. Genes associated with chlorophyll metabolism, flavonoid metabolism, photosynthesis, and signaling pathways were found to play crucial roles in leaf yellowing. In conclusion, this study delineated the phenotypic, physiological, cytological, and transcriptomic differences between YL and WT leaves, offering novel insights into the mechanisms driving leaf yellowing in Magnolia sinostellata.

CfSGR1 and CfSGR2 from Cryptomeria fortunei exhibit contrasting responses to hormones and abiotic stress in transgenic Arabidopsis

Stay-green (SGR) genes are pivotal regulatory genes in the context of plant chlorophyll metabolism, but few studies on SGR homologues in Cryptomeria fortunei have been previously reported. We cloned two CfSGR genes and overexpressed them in Arabidopsis to explore their functions. Full-length CfSGR1 and CfSGR2 are 1265 and 1197 bp, encompassing open reading frames (ORFs) encoding 274 and 276 amino acids, respectively. SGRs exhibited high conservation in higher plants, and phylogenetic analysis indicated that SGRs from monocots and gymnosperms cluster in a clade. The proteins localized to chloroplasts and showed no transcriptional activity in yeast cells. The CfSGR gene expressions were induced by abiotic stresses and hormones. Under conditions of darkness, abscisic acid (ABA), salt, drought, or freezing stress, CfSGR2-transgenic Arabidopsis exhibited a delay in leaf yellowing compared to the WT, which was attributed to increased chlorophyll content and enhanced photosynthetic capacity. These transgenic plants exhibited improved resistance to stress via upregulated expression of resistance-related genes, increased antioxidant enzyme activities, and reduced malondialdehyde content and electrolyte leakage rate. In contrast, CfSGR1-transgenic plants may accelerate leaf yellowing and exhibit reduced stress resistance. Our findings highlight potential divergence in the functions of CfSGR genes concerning plant growth and development and responses to abiotic stresses or hormones, providing a scientific foundation for future breeding of stress-resistant C. fortunei cultivars.

Effects of abiotic stress on chlorophyll metabolism

Chlorophyll, an essential pigment in the photosynthetic machinery of plants, plays a pivotal role in the absorption of light energy and its subsequent transfer to reaction centers. Given that the global production of chlorophyll reaches billions of tons annually, a comprehensive understanding of its biosynthetic pathways and regulatory mechanisms is important. The metabolic pathways governing chlorophyll biosynthesis and catabolism are complex, encompassing a series of interconnected reactions mediated by a spectrum of enzymes. Environmental fluctuations, particularly abiotic stressors such as drought, extreme temperature variations, and excessive light exposure, can significantly perturb these processes. Such disruptions in chlorophyll metabolism have profound implications for plant growth and development. This review delves into the core aspects of chlorophyll metabolism, encompassing both biosynthetic and degradative pathways. It elucidates key genes and enzymes instrumental in these processes and underscores the impact of abiotic stress on chlorophyll metabolism. Furthermore, the review aims to deepen the understanding of the interplay between chlorophyll metabolic dynamics and stress responses, thereby shedding light on potential regulatory mechanisms.

Loss-of-function of PGL10 impairs photosynthesis and tolerance to high-temperature stress in rice

High temperature (HT) affects the production of chlorophyll (Chl) pigment and inhibits cellular processes that impair photosynthesis, and growth and development in plants. However, the molecular mechanisms underlying heat stress in rice are not fully understood yet. In this study, we identified two mutants varying in leaf color from the ethylmethanesulfonate mutant library of indica rice cv. Zhongjiazao-17, which showed pale-green leaf color and variegated leaf phenotype under HT conditions. Mut-map revealed that both mutants were allelic, and their phenotype was controlled by a single recessive gene PALE GREEN LEAF 10 (PGL10) that encodes NADPH:protochlorophyllide oxidoreductase B, which is required for the reduction of protochlorophyllide into chlorophyllide in light-dependent tetrapyrrole biosynthetic pathway-based Chl synthesis. Overexpression-based complementation and CRISPR/Cas9-based knockout analyses confirmed the results of Mut-map. Moreover, qRT-PCR-based expression analysis of PGL10 showed that it expresses in almost all plant parts with the lowest expression in root, followed by seed, third leaf, and then other green tissues in both mutants, pgl10a and pgl10b. Its protein localizes in chloroplasts, and the first 17 amino acids from N-terminus are responsible for signals in chloroplasts. Moreover, transcriptome analysis performed under HT conditions revealed that the genes involved in the Chl biosynthesis and degradation, photosynthesis, and reactive oxygen species detoxification were differentially expressed in mutants compared to WT. Thus, these results indicate that PGL10 is required for maintaining chloroplast function and plays an important role in rice adaptation to HT stress conditions by controlling photosynthetic activity.

Comparative Physio-Biochemical and Transcriptome Analyses Reveal Contrasting Responses to Magnesium Imbalances in Leaves of Mulberry (Morus alba L.) Plants

Magnesium (Mg) deficiency is a major factor limiting the growth and development of plants. Mulberry (Morus alba L.) is an important fruit tree crop that requires Mg for optimal growth and yield, especially in acid soils. However, the molecular mechanism of Mg stress tolerance in mulberry plants remains unknown. In this study, we used next-generation sequencing technology and biochemical analysis to profile the transcriptome and physiological changes of mulberry leaves under different Mg treatments (deficiency: 0 mM, low: 1 mM, moderate low: 2 mM, sufficiency: 3 mM, toxicity: 6 mM, higher toxicity: 9 mM) as T1, T2, T3, CK, T4, T5 treatments, respectively, for 20 days. The results showed that Mg imbalance altered the antioxidant enzymatic activities, such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), and non-enzymatic, including soluble protein, soluble sugar, malondialdehyde (MDA), and proline (PRO), contents of the plant. The Mg imbalances disrupted the ultrastructures of the vital components of chloroplast and mitochondria relative to the control. The transcriptome data reveal that 11,030 genes were differentially expressed (DEGs). Genes related to the photosynthetic processes (CAB40, CAB7, CAB6A, CAB-151, CAP10A) and chlorophyll degradation (PAO, CHLASE1, SGR) were altered. Antioxidant genes such as PER42, PER21, and PER47 were downregulated, but DFR was upregulated. The carbohydrate metabolism pathway was significantly altered, while those involved in energy metabolism processes were perturbed under high Mg treatment compared with control. We also identified several candidate genes associated with magnesium homeostasis via RT-qPCR validation analysis, which provided valuable information for further functional characterization studies such as promoter activity assay or gene overexpression experiments using transient expression systems.

Application of Multi-Omics Technologies to the Study of Phytochromes in Plants

Phytochromes (phy) are distributed in various plant organs, and their physiological effects influence plant germination, flowering, fruiting, and senescence, as well as regulate morphogenesis throughout the plant life cycle. Reactive oxygen species (ROS) are a key regulatory factor in plant systemic responses to environmental stimuli, with an attractive regulatory relationship with phytochromes. With the development of high-throughput sequencing technology, omics techniques have become powerful tools, and researchers have used omics techniques to facilitate the big data revolution. For an in-depth analysis of phytochrome-mediated signaling pathways, integrated multi-omics (transcriptomics, proteomics, and metabolomics) approaches may provide the answer from a global perspective. This article comprehensively elaborates on applying multi-omics techniques in studying phytochromes. We describe the current research status and future directions on transcriptome-, proteome-, and metabolome-related network components mediated by phytochromes when cells are subjected to various stimulation. We emphasize the importance of multi-omics technologies in exploring the effects of phytochromes on cells and their molecular mechanisms. Additionally, we provide methods and ideas for future crop improvement.