The DnaJ1 heat shock protein interacts with the flavanone 3‐hydroxylase‐like protein <scp>F3HL</scp> to synergistically enhance drought tolerance by scavenging reactive oxygen species in tomato

The widely distributed heat shock protein DnaJ is renowned for its pivotal role in enhancing thermal tolerance in plants; however, its involvement in drought tolerance remains elusive. In this study, genes encoding DnaJ1 were cloned from drought-resistant wild tomato (Solanum pennellii) and drought-sensitive cultivated tomato (Solanum lycopersicum). SpDnaJ1 and SlDnaJ1 from both tomato species were localized in the chloroplast, and their gene expression was induced by various abiotic stresses. SpDnaJ1 was found to be a more potent regulator than SlDnaJ1 in oxidative stress tolerance when expressed in yeast cells. Overexpression of SpDnaJ1 was demonstrated to confer drought tolerance in transgenic plants of cultivated tomato. These transgenic plants exhibited reduced relative conductivity, leaf water loss rate, and malondialdehyde content as compared to the wild-type plants following drought treatment. RNA-seq analysis revealed that overexpression of SpDnaJ1 primarily affects the expression of genes associated with antioxidants, protease inhibitors, and MAPK signaling in response to drought stress. Screening of a tomato cDNA library in the yeast two-hybrid system identified a flavanone 3-hydroxylase-like protein (F3HL) as an interacting protein of DnaJ1. Subsequent findings revealed that F3HL enhances drought tolerance in tomato by increasing the activity of antioxidant enzymes and scavenging reactive oxygen species. These findings demonstrate a pivotal role of DnaJ1-F3HL interaction in enhancing drought tolerance, unveiling a novel molecular mechanism in drought tolerance in plants.