Control of chloroplast integrity by the jasmonate signaling pathway is linked to growth-defense balance

The lipid-derived signal jasmonate (JA) controls growth-defense balance by modulating the abundance of JAZ proteins that repress MYC transcription factors. In Arabidopsis, the JAZ-MYC regulon also promotes JA-induced degreening of detached leaves under conditions of dark-induced starvation. These observations, together with the finding that JA biosynthesis and signaling mutants do not exhibit obvious defects in natural senescence, have confounded a satisfactory explanation of the physiological significance of JA-induced chlorosis. Using intact Arabidopsis plants grown under normal laboratory conditions, we manipulated JAZ abundance to investigate JA-induced degreening as a component of the leaf growth-defense syndrome. A jaz decuple mutant (jazD) lacking most JAZs exhibited strong growth-defense tradeoffs without visible symptoms of senescence. Further depletion of JAZ by treatment of jazD with coronatine recapitulated the major hallmarks of senescence, including the loss of chlorophyll and photosynthetic capacity, turnover of chloroplast proteins and lipids, and transition of chloroplasts to gerontoplasts. The data highlight the regulation of senescence by jasmonate signaling along the growth-defense continuum. To examine the transcriptional responses of jazD during coronatine-induced degreening, jazD were treated with coronatine or a mock (control/reference) solution and expression was examined over a 24 hour time course (0, 1, 3, 12, and 24 hours). Three replicates were sampled for each time point and treatment for 30 total samples. We performed treated versus untreated comparisons at each time point.