Abstract
Abscisic acid (ABA) largely promotes leaf senescence and inhibits seed germination in plants. Endogenous ABA content is finely tuned by many transcription factors. In this study, we showed that OsWRKY53 is a positive regulator of leaf senescence and a negative regulator of seed germination in rice. OsWRKY53 expression was induced in leaves under aging, dark, and ABA treatment. The OsWRKY53-overexpressing (OsWRKY53-oe) plants showed early yellowing leaves, while the OsWRKY53 (oswrky53) knockout mutants maintained green leaves than the wild type under natural, dark-induced, and ABA-induced senescence conditions. Transcriptional analysis revealed that ABA catabolic genes, namely, OsABA8ox1 and OsABA8ox2, two key genes participating in ABA catabolism harboring ABA 8′-hydroxylase activity, were markedly downregulated in OsWRKY53-oe leaves. Chromatin immunoprecipitation and protoplast transient assays revealed that OsWRKY53 directly bound to the promoters of OsABA8ox1 and OsABA8ox2 to repress their transcription, resulting in elevated endogenous ABA contents that promoted premature leaf senescence in the OsWRKY53-oe plants. It indicates that OsWRKY53 is a positive regulator through regulating ABA accumulation to promote leaf senescence. In addition, accumulated ABA simultaneously inhibited seed germination and post-germination growth in OsWRKY53-oe plants. Taken together, OsWRKY53 suppresses the transcript of ABA catabolic genes to promote ABA accumulation to modulate ABA-induced leaf senescence and ABA-mediated inhibition of seed germination.
Highlights
Leaf senescence, the final stage of leaf development, is featured with developmentally programmed leaves yellowing due to the loss of green pigment chlorophyll (Lim et al, 2007; Woo et al, 2019)
RT-qPCR assays showed that four chlorophyll degradation gene and three senescence-associated genes (SAGs) had higher transcript levels in OsWRKY53-oe plants, but lower levels in oswrky53 mutants relative to them in wild type (Figures 1E,F)
In line with OsWRKY53 regulating leaf senescence, OsWRKY53 had the highest transcript levels in leaf and sheath rather than in other tissues (Supplementary Figure 1). These results indicate that OsWRKY53 is positively involved in natural leaf senescence
Summary
The final stage of leaf development, is featured with developmentally programmed leaves yellowing due to the loss of green pigment chlorophyll (Lim et al, 2007; Woo et al, 2019). Leaf senescence is controlled by multiple genetic and. OsWRKY53 Regulates ABA-Mediated Leaf Senescence environmental factors. The major genetic factors are termed senescence-associated genes (SAGs), which exhibit accumulated gene expressions during leaf senescence. Many SAGs have been characterized in rice. They are involved in nutrient relocation, macromolecules degradation, transcriptional regulation, and signal transduction (Lee and MasclauxDaubresse, 2021). Rice plants containing these loss-of-function or gain-of-function SAGs usually exhibit delayed or accelerated leaf senescence. Environmental factors including nutrient status, light quality and length, climate change, water usage, and biotic stress separately or collaboratively modulate leaf senescence (Lee and Masclaux-Daubresse, 2021)
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