Genome-wide characterization of homeobox-leucine zipper gene family in tomato (Solanum lycopersicum) and functional analysis of SlHDZ34 (III sub-family member) under salinity stress

High salinity is one of the major environment factors threatening crop productivity and quality. Identification and function characterization of stress-related transcription factors (TFs) can provide genetic resources for transgenic plants to improve their tolerance to salt stress. In this study, a total of 49 Homeodomain-leucine zipper (HD-ZIP) genes in the tomato genome were identified and the expression profiling of all HD-Zip III members under salt and hormone treatments was investigated. A member of the HD-Zip III sub-family, Solanum lycopersicon homeodomain-leucine zipper 34 (SlHDZ34), significantly responded to salt stress. Under salinity, compared with control, silencing SlHDZ34 in tomato inhibited plant growth, including shorter plant height and less dry weight of shoot and root; promoted the accumulation of reactive oxygen species (ROS) leading to severe oxidative damage; in addition, lower photosynthetic rates and reduced abscisic acid (ABA) biosynthetic genes expressions were detected in SlHDZ34-silenced plants. Collectively, our findings revealed that SlHDZ34 plays a critical role in tomato tolerance to salinity stress. Our work can provide a promising candidate for future breeding salt-tolerant tomatoes.