Transcription factor LbWOX5 improves salt tolerance by regulating salt gland development in <i>Limonium bicolor</i>

Abstract WUSCHEL-related homeobox (WOX) transcription factors play a key role in regulating plant growth, development, and stress responses. However, the role of WOX proteins in regulating salt gland development and salt tolerance in Limonium bicolor remains unexplored. In this study, we identified 17 LbWOX genes and classified them into three phylogenetic clades. To identify key regulators of salt gland development, we silenced candidate genes; plants with LbWOX5 silenced exhibited significantly fewer salt glands compared with controls. Furthermore, overexpression and silencing of LbWOX5 revealed that LbWOX5 positively regulates salt gland development and salt tolerance. We determined that LbWOX5 is mainly expressed in salt glands and LbWOX5 localizes in the nucleus. Further study revealed that LbWOX5 binds specifically to the Cullin1 (LbCUL1) promoter and activates its expression. Silencing of LbCUL1 led to significantly lower salt gland density and salt tolerance, while its overexpression promoted salt gland development and improved salt tolerance. Silencing both LbWOX5 and LbCUL1 simultaneously did not produce a more pronounced effect on salt gland density or salt tolerance than silencing either gene alone. This study showed that LbWOX5 promotes salt gland development and salt tolerance in L. bicolor by activating LbCUL1. This LbWOX5–LbCUL1 regulatory module provides a potential genetic basis for engineering crops with enhanced salt tolerance.