AhHDA1-mediated AhGLK1 promoted chlorophyll synthesis and photosynthesis regulates recovery growth of peanut leaves after water stress

Plastid- and photoreceptor-dependent signaling is required for the response to photoperiod stress

Prolongation of the light period causes photoperiod stress in plants. The response to photoperiod stress includes the induction of a distinct set of stress marker genes, of reactive oxygen species (ROS), and of stress hormones. In this study, the impact of light intensity and light quality on the photoperiod stress response was investigated. A threshold light intensity of circa 50 μmol m-2 s-1 is necessary for inducing photoperiod stress, indicating the involvement of chloroplasts. Lower photoperiod stress symptoms in retrograde signaling mutants (gun4, gun5) and mutants with constrained plastid function (glk1 glk2) corroborated the role of chloroplasts. Genetic analysis revealed that the photoreceptors phyB and particularly CRY2 are important to perceive photoperiod stress. Overall, these results showed that both plastid-dependent and photoreceptor-dependent signaling pathways are involved in sensing the light conditions causing photoperiod stress and governing the response to it.

The pleiotropic functions of GOLDEN2-LIKE transcription factors in plants

The regulation of gene expression is crucial for biological plant growth and development, with transcription factors (TFs) serving as key switches in this regulatory mechanism. GOLDEN2-LIKE (GLK) TFs are a class of functionally partially redundant nuclear TFs belonging to the GARP superfamily of MYB TFs that play a key role in regulating genes related to photosynthesis and chloroplast biogenesis. Here, we summarized the current knowledge of the pleiotropic roles of GLKs in plants. In addition to their primary functions of controlling chloroplast biogenesis and function maintenance, GLKs have been proven to regulate the photomorphogenesis of seedlings, metabolite synthesis, flowering time, leaf senescence, and response to biotic and abiotic stress, ultimately contributing to crop yield. This review will provide a comprehensive understanding of the biological functions of GLKs and serve as a reference for future theoretical and applied studies of GLKs.

A Genome-Wide Analysis of the Jasmonic Acid Biosynthesis Gene Families in Peanut Reveals Their Crucial Roles in Growth and Abiotic Stresses

Abiotic stress is a limiting factor in peanut production. Peanut is an important oil crop and cash crop in China. Peanut yield is vulnerable to abiotic stress due to its seeds grown underground. Jasmonic acid (JA) is essential for plant growth and defense against adversity stresses. However, the regulation and mechanism of the jasmonic acid biosynthesis pathway on peanut defense against abiotic stresses are still limitedly understood. In this study, a total of 64 genes encoding key enzymes of JA biosynthesis were identified and classified into lipoxygenases (AhLOXs), alleno oxide synthases (AhAOSs), allene oxide cyclases (AhAOCs), and 12-oxo-phytodienoic acid reductases (AhOPRs) according to gene structure, conserved motif, and phylogenetic feature. A cis-regulatory element analysis indicated that some of the genes contained stress responsive and hormone responsive elements. In addition to proteins involved in JA biosynthesis and signaling, they also interacted with proteins involved in lipid biosynthesis and stress response. Sixteen putative Ah-miRNAs were identified from four families targeting 35 key genes of JA biosynthesis. A tissue expression pattern analysis revealed that AhLOX2 was the highest expressed in leaf tissues, and AhLOX32 was the highest expressed in shoot, root, and nodule tissues. AhLOX16, AhOPR1, and AhOPR3 were up-regulated under drought stress. AhLOX16, AhAOS3, AhOPR1, and AhAOC4 had elevated transcript levels in response to cold stress. AhLOX5, AhLOX16, AhAOC3, AhOPR1, and AhOPR3 were up-regulated for expression under salt stress. Our study could provide a reference for the study of the abiotic stress resistance mechanism in peanut.

Transcriptome Analysis Reveals the Molecular Mechanism of the Leaf Yellowing in Allotriploid Cucumber

Yellowing leaves are ideal materials for studying the metabolic pathways of photosynthetic pigment chloroplast development, and the mechanism of photosynthetic systems. Here, we obtained a triploid material HCC (2n = 3x = 26), which was derived from hybridization between the artificial tetraploid Cucumis × hytivus (2n = 4x = 38, HHCC) and the cultivated cucumber Cucumis sativus (2n = 2x = 14, CC), and this triploid HCC showed obvious leaf yellowing characteristics. Phenotypic observation results showed that chloroplast development was impaired, the chlorophyll content decreased, and photosynthesis decreased in yellowing HCC leaves. The transcriptome results indicated that HCC-GLK is significantly downregulated in HCC and participates in the regulation of leaf yellowing. GO enrichment analysis revealed that differential genes were enriched in the heme binding and tetrapyrrole binding pathways related to leaf color. KEGG enrichment analysis revealed that differential genes were predominantly enriched in photosynthesis-related pathways. The experimental results of VIGS and yeast hybridization showed that silencing the GLK gene can induce leaf yellowing in cucumber plants, and the GLK protein can affect plant chloroplast development by interacting with the CAB3C protein (light-harvesting chlorophyll a/b binding) in the plant chlorophyll synthesis pathway. The current findings have not only enhanced our understanding of the regulatory mechanism of the GLK transcription factor in cucumber but also introduced novel insights and directions for investigating the molecular mechanism underlying polyploid leaf yellowing.

Changes in epigenetic features in legumes under abiotic stresses

Legume crops are rich in nutritional value for human and livestock consumption. With global climate change, developing stress-resilient crops is crucial for ensuring global food security. Because of their nitrogen-fixing ability, legumes are also important for sustainable agriculture. Various abiotic stresses, such as salt, drought, and elevated temperatures, are known to adversely affect legume production. The responses of plants to abiotic stresses involve complicated cellular processes including stress hormone signaling, metabolic adjustments, and transcriptional regulations. Epigenetic mechanisms play a key role in regulating gene expressions at both transcriptional and posttranscriptional levels. Increasing evidence suggests the importance of epigenetic regulations of abiotic stress responses in legumes, and recent investigations have extended the scope to the epigenomic level using next-generation sequencing technologies. In this review, the current knowledge on the involvement of epigenetic features, including DNA methylation, histone modification, and noncoding RNAs, in abiotic stress responses in legumes is summarized and discussed. Since most of the available information focuses on a single aspect of these epigenetic features, integrative analyses involving omics data in multiple layers are needed for a better understanding of the dynamic chromatin statuses and their roles in transcriptional regulation. The inheritability of epigenetic modifications should also be assessed in future studies for their applications in improving stress tolerance in legumes through the stable epigenetic optimization of gene expressions.

Withdrawn as duplicate: Shade represses photosynthetic genes by disrupting the DNA binding of GOLDEN2-LIKE1

This article has been withdrawn due to an error that caused the article to be duplicated. The definitive version of this article is published under DOI https://doi.org/10.1093/plphys/kiad029.

Histone deacetylase 9 regulates disease resistance through fine-tuning histone deacetylation of melatonin biosynthetic genes and melatonin accumulation in cassava

Melatonin participates in plant growth and development and biotic and abiotic stress responses. Histone acetylation regulates many plant biological processes via transcriptional reprogramming. However, the direct relationship between melatonin and histone acetylation in plant disease resistance remains unclear. In this study, we identified cassava bacterial blight (CBB) responsive histone deacetylase 9 (HDA9), which negatively regulated disease resistance to CBB by reducing melatonin content. In addition, exogenous melatonin alleviated disease sensitivity of MeHDA9 overexpressed plants to CBB. Importantly, MeHDA9 inhibited the expression of melatonin biosynthetic genes through decreasing lysine 5 of histone 4 (H4K5) acetylation at the promoter regions of melatonin biosynthetic genes, thereby modulating melatonin accumulation in cassava. Furthermore, protein phosphatase 2C 12 (MePP2C12) interacted with MeHDA9 in vivo and in vitro, and it was involved in MeHDA9-mediated disease resistance via melatonin biosynthetic pathway. In summary, this study highlights the direct interaction between histone deacetylation and melatonin biosynthetic genes in cassava disease resistance via histone deacetylation, providing new insights into the genetic improvement of disease resistance via epigenetic regulation of melatonin level in tropical crops.

Transcriptome profiling reveals characteristics of hairy root and the role of AhGLK1 in response to drought stress and post-drought recovery in peanut

BACKGROUND

HR (hairy root) has emerged as a valuable tissue for the rapid characterization of plant gene function and enzyme activity in vivo. AhGLK1 (Arachis hypogaea L. golden2-like 1) is known to play a role in post-drought recovery. However, it is unclear (a) whether HR has properties that are distinct from those of PR (primary root); and (b) which gene networks are regulated by AhGLK1 in response to drought stress and recovery in peanut.

RESULTS

We found that cells of the root tip cortex were larger in HR than in PR, while a total of 850 differentially expressed genes (DEGs) were identified in HR compared to PR. Eighty-eight of these DEGs, relating to chlorophyll and photosynthesis, were upregulated in HR. In addition, AhGLK1-OX (AhGLK1-overexpressing) HR showed a green phenotype, and had a higher relative water content than 35 S::eGFP (control) HR during drought stress. RNA-seq analysis showed that 74 DEGs involved both in the drought response and the post-drought recovery process were significantly enriched in the galactose metabolism pathway. GO terms enrichment analysis revealed that 59.19%, 29.79% and 17.02% of the DEGs mapped to the 'biological process' (BP), 'molecular function' (MF) and 'cellular component' (CC) domains, respectively. Furthermore, 20 DEGs involved in post-drought recovery were uniquely expressed in AhGLK1-OX HR and were significantly enriched in the porphyrin metabolism pathway. GO analysis showed that 42.42%, 30.30% and 27.28% of DEGs could be assigned to the BP, MF and CC domains, respectively. Transcription factors including bHLH and MYB family members may play a key role during drought stress and recovery.

CONCLUSION

Our data reveal that HR has some of the characteristics of leaves, indicating that HR is suitable for studying genes that are mainly expressed in leaves. The RNA-seq results are consistent with previous studies that show chlorophyll synthesis and photosynthesis to be critical for the role of AhGLK1 in improving post-drought recovery growth in peanut. These findings provide in-depth insights that will be of great utility for the exploration of candidate gene functions in relation to drought tolerance and/or post-drought recovery ability in peanut.

OsWR2 recruits HDA704 to regulate the deacetylation of H4K8ac in the promoter of OsABI5 in response to drought stress

Drought stress is a major environmental factor that limits the growth, development, and yield of rice (Oryza sativa L.). Histone deacetylases (HDACs) are involved in the regulation of drought stress responses. HDA704 is an RPD3/HDA1 class HDAC that mediates the deacetylation of H4K8 (lysine 8 of histone H4) for drought tolerance in rice. In this study, we show that plants overexpressing HDA704 (HDA704-OE) are resistant to drought stress and sensitive to abscisic acid (ABA), whereas HDA704 knockout mutant (hda704) plants displayed decreased drought tolerance and ABA sensitivity. Transcriptome analysis revealed that HDA704 regulates the expression of ABA-related genes in response to drought stress. Moreover, HDA704 was recruited by a drought-resistant transcription factor, WAX SYNTHESIS REGULATORY 2 (OsWR2), and co-regulated the expression of the ABA biosynthesis genes NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3), NCED4, and NCED5 under drought stress. HDA704 also repressed the expression of ABA-INSENSITIVE 5 (OsABI5) and DWARF AND SMALL SEED 1 (OsDSS1) by regulating H4K8ac levels in the promoter regions in response to polyethylene glycol 6000 treatment. In agreement, the loss of OsABI5 function increased resistance to dehydration stress in rice. Our results demonstrate that HDA704 is a positive regulator of the drought stress response and offers avenues for improving drought resistance in rice.

The Role of Membranes and Lipid-Protein Interactions in the Mg-Branch of Tetrapyrrole Biosynthesis

Chlorophyll (Chl) is essential for photosynthesis and needs to be produced throughout the whole plant life, especially under changing light intensity and stress conditions which may result in the destruction and elimination of these pigments. All steps of the Mg-branch of tetrapyrrole biosynthesis leading to Chl formation are carried out by enzymes associated with plastid membranes. Still the significance of these protein-membrane and protein-lipid interactions in Chl synthesis and chloroplast differentiation are not very well-understood. In this review, we provide an overview on Chl biosynthesis in angiosperms with emphasis on its association with membranes and lipids. Moreover, the last steps of the pathway including the reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), the biosynthesis of the isoprenoid phytyl moiety and the esterification of Chlide are also summarized. The unique biochemical and photophysical properties of the light-dependent NADPH:protochlorophyllide oxidoreductase (LPOR) enzyme catalyzing Pchlide photoreduction and located to peculiar tubuloreticular prolamellar body (PLB) membranes of light-deprived tissues of angiosperms and to envelope membranes, as well as to thylakoids (especially grana margins) are also reviewed. Data about the factors influencing tubuloreticular membrane formation within cells, the spectroscopic properties and the in vitro reconstitution of the native LPOR enzyme complexes are also critically discussed.