Removal of DELLA repression promotes leaf senescence in Arabidopsis

Leaf senescence is an integrated response of leaf cells to developmental age and various internal and environmental signals. However, the role of gibberellins (GA) in leaf senescence is not clear. In the current study, we investigated the effect of DELLA on leaf senescence. Compared with the wild type (WT), leaf senescence occurred earlier in the mutant gal-3 gai-t6 rga-t2 rgl1-1 rgl2-1 (abbreviated as Q-DELIAlga13) whose DELLA repression was removed, whereas leaf senescence was retarded in the mutant gal-3 whose GA biosynthesis was blocked and whose DELLA proteins accumulated abnormally. During leaf senescence, SAG12 and SAG29 were upregulated in Q-DELIA/gal-3 and downregulated in gal-3 plants. The Q-DELLAIgal-3 senescent leaves contained more sugar but less chlorophyll and fatty acids (FAs) than those of gal-3 and WT. Both absolute and relative contents of C18:3 in Q-DELLAIga1-3 senescent leaves were lower compared with those of the WT and gal-3 leaves. The genes regulating FA beta-oxidation in Q-DELLAIgal-3, such as KM, IACS6, IACS7, AGO, ACX2 and MAP2, were significantly upregulated. The removal of DELLA repression highly upregulated certain genes on various hormone pathways, suggesting that GA signaling acts upstream of the jasmonic acid, salicylic acid, and ethylene pathways in regulating leaf senescence. (c) 2014 Elsevier Ireland Ltd. All rights reserved.