Mycorrhizal cucumber with Diversispora versiformis has active heat stress tolerance by up-regulating expression of both CsHsp70s and CsPIPs genes

Abstract

Cucumbers are frequently subjected to heat stress (HS) during the summer, which severely limits their growth and fruit yield and quality. Soil arbuscular mycorrhizal fungi (AMF) can enhance the abiotic stress tolerance of host plants, but it is unclear whether and how soil arbuscular mycorrhizal fungi (AMF) enhance the HS tolerance of cucumber. This work aimed to assess the effects of an arbuscular mycorrhizal fungus, Diversispora versiformis, on plant growth, leaf gas exchange, and expressions of plasma membrane intrinsic proteins (PIPs) and heat shock protein 70 (Hsp70) genes in roots of cucumber under HS (38 °C/30 °C, day/night temperature, 16 h/8 h) and suitable temperature (ST) (25 °C/18 °C, day/night temperature, 16 h/8 h) conditions. The HS treatment significantly decreased root mycorrhizal colonization and soil mycelium length by 0.26- and 0.55-fold, respectively, compared with the ST treatment. The biomass inhibition of cucumber by HS versus ST was more pronounced in uninoculated plants than inoculated plants. Inoculation with D. versiformis, however, significantly increased cucumber biomass and leaf gas exchange under both ST and HS conditions when compared to the uninoculated treatment. The HS treatment had almost no effect on or down-regulated the expression of CsHsp70s and CsPIPs genes in uninoculated plants, while most CsHsp70s and CsPIPs gene expressions were up-regulated in inoculated plants under HS versus ST conditions, suggesting the active heat resistance of mycorrhizal plants. Additionally, under ST conditions, D. versiformis up-regulated CsHsp70–11, CsPIP1;2, and CsPIP2;6 expressions. Under HS conditions, D. versiformis increased the expression of 11 of 12 CsHsp70s by 1.17‒6.14 folds as well as 12 of 14 CsPIPs by 1.82‒144.43 folds, with CsPIP1.5 and CsPIP2;7 up-regulated up to 144.43- and 82.46-fold, respectively. It is concluded that D. versiformis-inoculated cucumbers exhibited higher heat tolerance than uninoculated plants, associated with up-regulated expression of most CsHsp70s and CsPIPs genes.