Abstract
Deoxyribonucleic acid (DNA) methylation is an important epigenetic mark involved in diverse biological processes. Here, we report the critical function of tomato (Solanum lycopersicum) Domains Rearranged Methyltransferase7 (SlDRM7) in plant growth and development, especially in leaf interveinal chlorosis and senescence. Using a hairpin RNA-mediated RNA interference (RNAi), we generated SlDRM7-RNAi lines and observed pleiotropic developmental defects including small and interveinal chlorosis leaves. Combined analyses of whole genome bisulfite sequence (WGBS) and RNA-seq revealed that silencing of SlDRM7 caused alterations in both methylation levels and transcript levels of 289 genes, which are involved in chlorophyll synthesis, photosynthesis, and starch degradation. Furthermore, the photosynthetic capacity decreased in SlDRM7-RNAi lines, consistent with the reduced chlorophyll content and repression of genes involved in chlorophyll biosynthesis, photosystem, and photosynthesis. In contrast, starch granules were highly accumulated in chloroplasts of SlDRM7-RNAi lines and associated with lowered expression of genes in the starch degradation pathway. In addition, SlDRM7 was activated by aging- and dark-induced senescence. Collectively, these results demonstrate that SlDRM7 acts as an epi-regulator to modulate the expression of genes related to starch and chlorophyll metabolism, thereby affecting leaf chlorosis and senescence in tomatoes.
Highlights
Leaf senescence, the final stage of leaf development prior to its death, is a genetically programmed degenerative process, which is accompanied by massive macromolecular catabolism and nutrient recycling to young or storage tissues (Gan and Amasino, 1997; Guo and Gan, 2005)
Considering the critical role of SlDRM7 in de novo RNA-directed DNA methylation (RdDM), it is possible that SlDRM7-RNA interference (RNAi) may impose some epigenetic remodeling of its target genes that are required for proper leaf development, and such epigenetic remodeling to control leaf chlorosis is not transgenerationally heritable but relies on constant RNAi of SlDRM7
We tested the SlDRM7 expression during age-dependent and dark-induced senescence in wild type (WT) plants and found that the transcript level of SlDRM7 was significantly upregulated in senescence leaves induced either naturally or darkly (Supplementary Figure 4). This finding seems contradictory to the genome-wide demethylation during plant senescence (Ogneva et al, 2016), suggesting a putative self-feedback pathway may be involved in regulating senescence by increasing SlDRM7 expression and a subsequently enhanced epi-control. These findings reveal that SlDRM7 is required for proper vegetative growth, where SlDRM7 may work as a negative epi-regulator to repress the transcriptional expression of senescence-associated genes, leading to sustain a photosynthetic capacity and inhibit the initiation of leaf senescence in tomatoes
Summary
The final stage of leaf development prior to its death, is a genetically programmed degenerative process, which is accompanied by massive macromolecular catabolism and nutrient recycling to young or storage tissues (Gan and Amasino, 1997; Guo and Gan, 2005). At the genetic transcriptional and post-transcriptional level, well-established senescence markers include chlorophyll content (Rossi et al, 2015), photochemical efficiency (Guo and Gan, 2005), starch metabolism (Caspar et al, 1985; Zeeman et al, 1998; Zeeman and Rees, 1999), and expression of senescenceassociated genes (SAGs) (Lim et al, 2007a). Histone modification and chromatin remodeling have been found to regulate certain SAGs expression at the transcriptional level (Lim et al, 2007b; Ay et al, 2009; Chen et al, 2016; Liu et al, 2019), implying a critical role of epigenetic control over leaf senescence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
