Unique miR775-GALT9 module regulates leaf senescence in Arabidopsis during post-submergence recovery by modulating Ethylene and Abscisic acid pathway

Submergence-induced hypoxic condition negatively affects the plant growth and development, and causes early onset of senescence. Hypoxia alters the expression of a number of microRNAs (miRNAs). However, the molecular function of submergence stress-induced miRNAs in physiological or developmental changes and recovery remains poorly understood. Here we show that miR775 is an Arabidopsis thaliana-specific young and unique miRNA that possibly evolved non-canonically. miR775 post-transcriptionally regulates Galactosyltransferase (GALT9) and their expression is inversely affected at 24 hours of complete submergence stress. The overexpression of miR775 (miR775-Oe) confers enhanced recovery from submergence stress and reduced accumulation of RBOHD and ROS, in contrast to wild type and MIM775 Arabidopsis shoot. A similar recovery phenotype of galt9 mutant indicates the role of miR775-GALT9 module in post-submergence recovery. We predicted Golgi-localized GALT9 to be potentially involved in protein glycosylation. The altered expression of senescence-associated genes (SAG12, SAG29, and ORE1), ethylene signalling (EIN2 and EIN3) and ABA biosynthesis (NCED3) pathway genes in miR775-Oe, galt9 and MIM775 plants. Thus, our results indicate the role of miR775-GALT9 module in post-submergence recovery through a crosstalk with ethylene and ABA pathway.