Heat shock protein and aquaporin expression enhance water conserving behavior of citrus under water deficits and high temperature conditions

Abstract

Citrus is most important fruit crop of the world grown throughout the subtropics and semi-arid to humid tropics. Water deficit and high temperature are two major abiotic stresses that affect the plant physiology negatively and ultimately reduced crop yield and performance. The objective of this study was to evaluate the responses of ten genetically diverse citrus selections against the water deficit, heat, and their combinations. Treatments consisted of moderate and high heat (38 °C and 46 °C), water deficit (50% and 25% field capacity) and combined (38 °C with 50% field capacity and 46 °C with 25% field capacity) stress. We measured the effects of water potential, moisture contents and gas exchange on the expression of heat shock proteins (HSPs) and major intrinsic proteins (MIPs). Brazilian sour orange (Citrus aurantium L.) and Keen sour orage (C. aurantium L) performed well by avoiding desiccation and maintaining photosynthesis, stomatal conductance, water potential and moisture content under high temperature and low soil moisture. While, Savage citrange (Poncirus trifoliata × Citrus sinensis) proved the most sensitive to all stress conditions. Genome wide analysis indicated that CsHsp70 had NBD sugar kinase actin Hsp70 protein and molecular charpones Dnak, while CsHsp70.1 had chloroplast protein with Dnak and CsHsp90 had Hsp90 protein. Brazilian sour orange expressed HSPs under heat, MIPs under water deficit and both under combined stress conditions. CsHsp70, CsHsp70.1 and CsHsp90 showed high expression from 1.5 to 6.0 h and then gradually decreased till 24.0 h under heat and combined stress in Brazilian sour orange. CsHsp70 in Savage citrange exhibited slight expression under heat and combined stress after 6.0 h. High expression of CsTIP2 and CsTIP1 was observed from 1.5 to 24.0 h under water deficit, whereas CsTIP1 expressed under heat and combined stress after 1.5 h. Whereas, Savage citrange exhibited little expression of the same genes under stress. It was concluded that the differences among these varieties are in tolerance to heat and water deficit is associated with capacity for upregulation of HSPs and MIPs.