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

•Plant physiology, plant water stress and plant morphology were severally affected by heat and deficit irrigation in citrus.•Water and heat responsive genes showed higher expression in tolerant and no or little expression in sensitive citrus genotypes.•Heat shock proteins and Major Intrinsic Proteins expression can contribute to avoiding the risks of oxidative stress incurred by water-conservative behavior in plant under stress.•Brazilian sour orange showed tolerance against heat, water deficit and combined heat and water deficit condition. 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 expr