Characterization of DEAD-box family of RNA helicases in tomato provides insights into their roles in biotic and abiotic stresses

In plants, RNA helicases play significant roles in growth, development and stress response. In a previous study, a three-fold upregulation of a DEAD-box RNA helicase in a tomato cultivar tolerant to Tomato leaf curl New Delhi virus (ToLCNDV) as compared to susceptible cultivar during virus infection was shown. Given this, a comprehensive study was performed to identify the members of RNA helicase family in tomato and analyze their functional properties in response to abiotic stresses, hormone treatments and ToLCNDV infection. A total of 131 genes were identified and classified into DEAD- (42), DEAH- (38), and DExD/H-box (51) RNA helicases. Expression profiling of candidate genes in response to abiotic stresses and ToLCNDV infection in contrasting tomato cultivars suggested the putative roles of SlDEAD23 and SlDEAD35 in biotic and abiotic stresses. Heterologous overexpression of these genes in yeast enhanced the tolerance of transgenic cells to salt and cold stresses. Further, virus-induced silencing of SlDEAD35 in ToLCNDV tolerant cultivar resulted in susceptibility to virus infection, thus suggesting its involvement in tolerance mechanism. Altogether, this study provides novel insights into the structure, organization and involvement of DEAD-box RNA helicase genes in biotic and abiotic stress responses in tomato