Heat shock proteins (HSPs) are molecular chaperones that play essential roles in plant development and in response to various environmental stresses. Understanding R. delavayi HSP genes is of great importance since R. delavayi is severely affected by heat stress. In the present study, a total of 76 RdHSP genes were identified in the R. delavayi genome, which were divided into five subfamilies based on molecular weight and domain composition. Analyses of the chromosome distribution, gene structure, and conserved motif of the RdHSP family genes were conducted using bioinformatics analysis methods. Gene duplication analysis showed that 15 and 8 RdHSP genes were obtained and retained from the WGD/segmental duplication and tandem duplication, respectively. Cis-element analysis revealed the importance of RdHSP genes in plant adaptations to the environment. Moreover, the expression patterns of RdHSP family genes were investigated in R. delavayi treated with high temperature based on our RNA-seq data, which were further verified by qRT-PCR. Further analysis revealed that nine candidate genes, including six RdHSP20 subfamily genes (RdHSP20.4, RdHSP20.8, RdHSP20.6, RdHSP20.3, RdHSP20.10, and RdHSP20.15) and three RdHSP70 subfamily genes (RdHSP70.15, RdHSP70.21, and RdHSP70.16), might be involved in enhancing the heat stress tolerance. The subcellular localization of two candidate RdHSP genes (RdHSP20.8 and RdHSP20.6) showed that two candidate RdHSPs were expressed and function in the chloroplast and nucleus, respectively. These results provide a basis for the functional characterization of HSP genes and investigations on the molecular mechanisms of heat stress response in R. delavayi.

Walnut bacterial blight caused by Xanthomonas arboricola pv. juglandis ( Xaj) is one of the most prevalent diseases of walnut ( Juglans spp.), causing significant reductions in nut yield and important losses in economy. Enoyl-acyl carrier protein (ACP) reductase (ENR) is one of the key enzymes involved in the biosynthesis of bacterial fatty acids. In this study, we identified a single ENR-encoding gene, RS10040, in the genome of the XajDW3F3 strain. Sequence alignment analysis suggested RS10040 as a candidate fabV gene in Xaj. Expression of XajfabV restored the growth of the Escherichia coli fabI temperature-sensitive mutant under a nonpermissive growth condition. In vitro assays demonstrated that XajFabV catalyzed enoyl-ACPs of various chain lengths to acyl-ACPs, demonstrating its role in de novo fatty acid biosynthesis. Furthermore, we confirmed that XajfabV is an essential gene for growth, as no XajfabV deletion mutant could be obtained, although XajfabV in the chromosome could be deleted after compensating with a functional ENR-encoding gene via an exogenous plasmid. The fabV replacement mutants showed similar growth characteristic and fatty acid compositions. Our data further identified that fabV conferred Xaj with tolerance to various environmental stresses. Although XajFabV conferred Xaj with triclosan resistance, the resistance of Xaj was weaker than that found for Pseudomonas aeruginosa. Moreover, triclosan exhibited a control effect against infection of the Δ fabV/EcfabI to its host walnut. This study revealed the function of XajFabV and laid a theoretical foundation for the fatty acid synthesis mechanism of Xaj.