The pectate lyase OsPSE1 mediates root cell-wall pectin turnover to regulate senescence in rice

Plant pectate lyases remodel the pectin matrix to drive cell expansion during plant growth and development. Here we show that OsPSE1, originally identified through the rice premature-senescence mutant ospse1, encodes an active pectate lyase that governs root pectin homeostasis and plant senescence. OsPSE1 is highly expressed in the root, where the wild-type OsPSE1 protein localizes primarily to the plasma membrane of root cells; however, the mutant ospse1 protein localizes almost exclusively to the nucleus. An in vitro depolymerase assay and quantitative tests showed that recombinant OsPSE1 protein has pectate lyase activity and can catalyze the degradation of polygalacturonic acid; the ospse1 protein shows reduced activity. Furthermore, ruthenium red staining, immunolabeling, and quantitative analysis revealed that the dysfunction of OsPSE1 causes abnormal accumulation of pectin and methyl-esterified homogalacturonan in the cell wall of rice root. Intriguingly, overexpression of OsPSE1 exhibits a significantly prolonged vegetative stage, compared to the wild type, with an extended reproductive stage and a longer overall growth period, which may be due to reduced pectin accumulation of roots and enhanced nutrient uptake in roots. Our findings indicate that the root pectin degradation regulated by the pectate lyase OsPSE1 is involved in rice plant senescence.