Overexpression of Purple Acid Phosphatase 2 Delays Dark-Induced Leaf Senescence in Arabidopsis thaliana

Senescence is the final stage of leaf development, which has an important impact on photosynthesis, nutrient redistribution, stress response, and so on. Drak-induced leaf senescence has been often employed as a model to study leaf senescence. In this study, we found that after dark-induced senescence, purple acid phosphatase 2 (PAP2) overexpressing lines (PAP2-OEs) remained higher chlorophyll (Chl) content, the maximum quantum yield of PSII photochemistry (F_v/F_m), and protein content, indicating PAP2-OEs leaves delayed senescence compared with wild-type (WT). These results seem inconsistent with previous reports, which showed overexpression of PAP2 promoted flowering and senescence. Quantitative real-time PCR (qRT-PCR) and RNA-seq results showed that the transcription levels of two genes encoding Chl degradation enzyme: NYC1, PAO, SGR2, and senescence-related genes SAG12, SAG13, and SAG21 were significantly lower, while the expression of senescence suppressor gene ESP was higher in PAP2-OE than in WT after dark incubation. Genes involved in sugar anabolism were higher in PAP2-OE-7, while genes induced by sugar starvation were significantly lower in PAP2-OE-7 than in WT. The transcription levels of genes involved in ethylene, jasmonic acid, abscisic acid synthesis, and signal transduction were also significantly lower in PAP2-OE-7. These findings suggest that overexpression of PAP2 increased the sugar content, which could delay dark-induced senescence in detached leaves by inhibiting the synthesis of senescence-related phytohormones.