Integration of transcriptomic and proteomic analyses reveals several levels of metabolic regulation in the excess starch and early senescent leaf mutant lses1 in rice

Suppressed OsPsbS1 expression triggers rice leaf senescence mediated by reactive oxygen species

Premature leaf senescence is an important factor affecting rice growth, development, and fitness. Although rice photosystem II subunit S (OsPsbS1) is a major gene controlling nonphotochemical quenching capacity (NPQ) in the photoprotective process, the role it plays in rice leaf senescence has not been explored yet. In this study, we use CRISPR/Cas9 technology to edit the OsPsbS1 gene, resulting in stable homozygous lines with premature leaf senescence. The Ospsbs1 mutant lines have pale-yellow leaves, reduced chlorophyll content, and show accelerated chloroplast degradation. Reactive oxygen species, malondialdehyde, superoxide dismutase, and peroxidase activity were significantly increased in the mutants, whereas ascorbate peroxidase and catalase activity, as well as chlorophyll content and photosynthetic rate, were markedly decreased. Furthermore, they showed increased expression of genes involved in senescence, ROS, and chlorophyll degradation. The Ospsbs1 mutant plants were found to have severe DNA degradation and programmed cell death through TUNEL and staining, suggesting that excess ROS may cause leaf senescence. RNA sequencing analysis revealed that OsPsbS1 is involved in the regulation of multiple biological processes, such as glutathione (GSH), starch and sucrose, and nitrogen metabolism pathways. Our results demonstrate that disruption of OsPsbS1 can accelerate leaf senescence as a result of over-accumulation of ROS. The discovery of OsPsbS1's function in controlling leaf aging in rice provides further genetic insights for understanding the molecular pathways that govern premature leaf senescence.

Genome-wide analysis of the FKBP gene family and the potential role of GhFKBP 13 in chloroplast biogenesis in upland cotton

BACKGROUND

In plants, FK506-binding proteins (FKBPs) have been shown to participate in various biological processes such as photosynthetic system reaction, stress response, and growth and development. However, the roles of FKBPs in cotton are less well known.

RESULTS

In this study, we investigated FKBP family genes on a genome-wide scale in four Gossypium species. A total of 147 FKBP genes were identified from these four Gossypium species and placed into three classes based on phylogenetic analysis. Collinearity analysis indicated that whole-genome duplication events and segmental duplication events were the main sources of gene amplification during the evolution of FKBP genes. Conserved motif, expression profiles and cis-acting elements prediction of the GhFKBPs analysis revealed that GhFKBPs were differentially expressed in different tissues and under abiotic stress. qRT-PCR analysis showed that some GhFKBPs were predominantly expressed in leaves. The analysis of cis-acting elements prediction revealed that MYB, MYC and ERE related binding sites in the promoters of GhFKBP genes were the most abundant. Furthermore, the composition and distribution of these cis-acting elements exhibited differences between homologous GhFKBP gene pairs. Silencing of GhFKBP13 in cotton resulted in disruption of chloroplast structure and starch metabolism disorders.

CONCLUSIONS

Taken together, 147 FKBP family genes in four Gossypium species are comprehensively characterized, and GhFKBP13 play a critical role in chloroplast biogenesis in upland cotton.

Identification of Novel Inhibitors of Starch Excess 4 (SEX4)

This study identified several inhibitors of Starch Excess 4 (SEX4), an enzyme in plants' starch decomposition. Our research aims to inhibit starch breakdown by SEX4 with its potential to significantly impact food security, leading to starch accumulation in plants such as potatoes, sweet potatoes, and significant crops like grains and rice. We recognized potential candidates by screening approximately 1840 chemical compounds using the phosphatase assay against pNPP. The IC50 values of the selected candidates were determined through the pNPP assay and the amylopectin assay, while Ki values were confirmed by calculating Vmax, KM, and kcat values. Finally, we compared the IC50 values of Like Sex Four 2 (LSF2) and SEX4 to assess their selectivity. This screening yielded several potential inhibitory compounds, with F05 showing promise in the pNPP assay and F09 and G11 in the amylopectin assay, all demonstrating more selectivity for SEX4 than LSF2. Consequently, we identified seven chemicals as promising inhibitor compounds, offering potential for future research and applications. However, further quantitative structure-activity relationship studies and the practical application to test selected compounds on crops will be necessary in future research.

The starch excess and key genes underlying citrus leaf chlorosis by rootstock-scion incompatibility

Leaf chlorosis caused by rootstock-scion incompatibility in citrus orchard badly affects fruit yield and quality. Starch excess and its key genes underlying citrus leaf chlorosis in incompatible graft remained unknown. Here, using created model incompatible/ compatible rootstock-scion combinations, we investigated starch content and distribution in 116 various chlorotic leaves of incompatible graft, and characterized the relationship between leaf chlorosis and starch accumulation. Further, we identified starch metabolism-related gene families by genome-wide analysis of pomelo genome, and performed comparative transcriptomic analysis on leaves. A total of nine key differentially expressed genes of starch metabolism were validated. Among them, seven starch synthesis-related genes were significantly upregulated, and two starch degradation-related genes, CgBAM4 and CgBAM6, were significantly downregulated. Meanwhile, the relative expression of synthesis-related genes was positively correlated with starch accumulation and leaf chlorosis. Using transient overexpression and VIGS experiments in pomelo, we confirmed the function of CgGBSS2, which was the only amylose synthesis-related key gene with the most significantly upregulated expression level. We proposed a working model to illustrate the regulatory network of starch excess accumulation involving in citrus leaf chlorosis of incompatible graft in the end. This study provides insights into the molecular mechanism underlying leaf chlorosis process in rootstock-scion incompatibility.

Genetic Analysis and Fine Mapping of a New Rice Mutant, Leaf Tip Senescence 2

Premature leaf senescence significantly reduces rice yields. Despite identifying numerous factors influencing these processes, the intricate genetic regulatory networks governing leaf senescence demand further exploration. We report the characterization of a stably inherited, ethyl methanesulfonate(EMS)-induced rice mutant with wilted leaf tips from seedling till harvesting, designated lts2. This mutant exhibits dwarfism and early senescence at the leaf tips and margins from the seedling stage when compared to the wild type. Furthermore, lts2 displays a substantial decline in both photosynthetic activity and chlorophyll content. Transmission electron microscopy revealed the presence of numerous osmiophilic granules in chloroplast cells near the senescent leaf tips, indicative of advanced cellular senescence. There was also a significant accumulation of H2O2, alongside the up-regulation of senescence-associated genes within the leaf tissues. Genetic mapping situated lts2 between SSR markers Q1 and L12, covering a physical distance of approximately 212 kb in chr.1. No similar genes controlling a premature senescence leaf phenotype have been identified in the region, and subsequent DNA and bulk segregant analysis (BSA) sequencing analyses only identified a single nucleotide substitution (C-T) in the exon of LOC_Os01g35860. These findings position the lts2 mutant as a valuable genetic model for elucidating chlorophyll metabolism and for further functional analysis of the gene in rice.

How abiotic stresses trigger sugar signaling to modulate leaf senescence?

Plants have evolved the adaptive capacity to mitigate the negative effect of external adversities at chemical, molecular, cellular, and physiological levels. This capacity is conferred by triggering the coordinated action of internal regulatory factors, in which sugars play an essential role in the regulating chloroplast degradation and leaf senescence under various stresses. In this review, we summarize the recent findings on the senescent-associated changes in carbohydrate metabolism and its relation to chlorophyl degradation, oxidative damage, photosynthesis inhibition, programmed cell death (PCD), and sink-source relation as affected by abiotic stresses. The action of sugar signaling in regulating the initiation and progression of leaf senescence under abiotic stresses involves interactions with various plant hormones, reactive oxygen species (ROS) burst, and protein kinases. This discussion aims to elucidate the complex regulatory network and molecular mechanisms that underline sugar-induced leaf senescence in response to various abiotic stresses. The imperative role of sugar signaling in regulating plant stress responses potentially enables the production of crop plants with modified sugar metabolism. This, in turn, may facilitate the engineering of plants with improved stress responses, optimal life span and higher yield achievement.

Mutations in starch biosynthesis genes affect chloroplast development in wheat pericarp

Starch bioengineering in cereals has produced a plethora of genotypes with new nutritional and technological functionalities. Modulation of amylose content from 0 to 100% was inversely correlated with starch digestibility and promoted a lower glycemic index in food products. In wheat, starch mutants have been reported to exhibit various side effects, mainly related to the seed phenotype. However, little is known about the impact of altered amylose content and starch structure on plant metabolism. Here, three bread wheat starch mutant lines with extreme phenotypes in starch branching and amylose content were used to study plant responses to starch structural changes. Omics profiling of gene expression and metabolic patterns supported changes, confirmed by ultrastructural analysis in the chloroplast of the immature seeds. In detail, the identification of differentially expressed genes belonging to functional categories related to photosynthesis, chloroplast and thylakoid (e.g. CURT1), the alteration in the accumulation of photosynthesis-related compounds, and the chloroplast alterations (aberrant shape, grana stacking alteration, and increased number of plastoglobules) suggested that the modification of starch structure greatly affects starch turnover in the chloroplast, triggering oxidative stress (ROS accumulation) and premature tissue senescence. In conclusion, this study highlighted a correlation between starch structure and chloroplast functionality in the wheat kernel.

Identification of the early leaf senescence gene ELS3 in bread wheat (Triticum aestivum L.)

MAIN CONCLUSION

Characterization of the early leaf senescence mutant els3 and identification of its causal gene ELS3, which encodes an LRR-RLK protein in wheat. Leaf senescence is an important agronomic trait that affects both crop yield and quality. However, few senescence-related genes in wheat have been cloned and functionally analyzed. Here, we report the characterization of the early leaf senescence mutant els3 and fine mapping of its causal gene ELS3 in wheat. Compared with wild-type Yanzhan4110 (YZ4110), the els3 mutant had a decreased chlorophyll content and a degraded chloroplast structure after the flowering stage. Further biochemical assays in flag leaves showed that the superoxide anion and hydrogen peroxide contents increased, while the activities of antioxidant enzymes, including catalase, superoxide dismutase and glutathione reductase, decreased gradually after the flowering stage in the els3 mutant. To clone the causal gene underlying the phenotype of leaf senescence, a genetic map was constructed using 10,133 individuals of F2:3 populations, and ELS3 was located in a 2.52 Mb region on chromosome 2DL containing 16 putative genes. Subsequent sequence analysis and gene annotation identified only one SNP (C to T) in the first exon of TraesCS2D02G332700, resulting in an amino acid substitution (Pro329Ser), and TraesCS2D02G332700 was preliminarily considered as the candidate gene of ELS3. ELS3 encodes a leucine-rich repeat receptor-like kinase (LRR-RLK) protein that is localized on the cell membrane. We also found that the transient expression of mutant TraesCS2D02G332700 can induce leaf senescence in N. benthamiana. Taken together, TraesCS2D02G332700 is likely to be the candidate gene of ELS3 and may have a function in regulating leaf senescence.