Jasmonic Acid Is Required for Plant Acclimation to a Combination of High Light and Heat Stress

In the field, plants experience high light (HL) intensities that are often accompanied by elevated temperatures. Such conditions are a serious threat to agriculture production, because photosynthesis is highly sensitive to both HL intensities and hightemperature stress. One of the potential cellular targets of HL and heat stress (HS) combination is PSII because its degree of photoinhibition depends on the balance between the rate of PSII damage (induced by light stress), and the rate of PSII repair (impaired under HS). Here, we studied the responses of Arabidopsis (Arabidopsis thaliana) plants to a combination of HL and HS (HL1HS) conditions. Combined HL1HS was accompanied by irreversible damage to PSII, decreased D1 (PsbA) protein levels, and an enhanced transcriptional response indicative of PSII repair activation. We further identified several unique aspects of this stress combination that included enhanced accumulation of jasmonic acid (JA) and JA-Ile, elevated expression of over 2,200 different transcripts that are unique to the stress combination (including many that are JA-associated), and distinctive structural changes to chloroplasts. A mutant deficient in JA biosynthesis (allene oxide synthase) displayed enhanced sensitivity to combined HL1HS and further analysis revealed that JA is required for regulating several transcriptional responses unique to the stress combination. Our study reveals that JA plays an important role in the acclimation of plants to a combination of HL1HS.