Silencing of fatty acid desaturase (FAD7) gene enhances membrane stability and photosynthetic efficiency under heat stress in tobacco (Nicotiana benthamiana)

Maintenance of cell membrane stability under heat stress is considered as an important adaptive mechanism. In this study, an attempt was made to improve membrane stability under high temperature stress through downregulation of fatty acid desaturase (FAD7) gene by post-transcriptional gene silencing (PTGS) approach using virus-induced gene silencing (VIGS) system in order to decrease trienoic fatty acids. Endogenous FAD7 gene fragment from Nicotiana benthamiana was cloned to construct VIGS vector (pTRV2: FAD7). The Agrobacterium strain harboring the pTRV2: FAD7 was infiltrated into 4-leaf stage N. benthamiana. The downregulation of FAD7 gene in VIGS plants were confirmed through semi quantitative RT-PCR. The FAD7 gene downregulated plants were exposed to normal and 35 and 42 degrees C temperature stress. In FAD7 silenced plants, the content of linolenic acid (18:3) decreased significantly, while linoleic acid (18:2) increased under high-temperature stress. FAD7 silenced plants showed higher net photosynthetic rate and PS-II efficiency under high-temperature stress as compared to control and empty vector transformed plants. Conversely, lower H2O2 content, membrane damage, electrolyte leakage and antioxidative enzyme activities were observed in silenced plants as compared to control. The FAD7 silenced plants exhibited better tolerance to high temperature than wild type due to higher dienoic to trienoic fatty acids ratio imparting membrane stability. The study concludes that alteration in fatty acid composition in thylakoid membranes can lower oxidative stress, improve photosynthetic rate, PS-II efficiency in plants under high temperature stress.