The LbBLH9-LbGeBP module regulates salt gland development and salt tolerance in Limonium bicolor

GLABROUS1 enhancer-binding protein (GeBP) transcription factors play pivotal roles in the regulating plant development and stress responses. However, the function of GeBP family members in regulating salt gland development and salt tolerance in Limonium bicolor remains unclear. In this study, the gene LbGeBP1 exhibited high expression levels during the early stages of salt gland development. We found that LbGeBP1 is mainly expressed in salt glands and LbGeBP1 localizes in the nucleus. Functional analysis through overexpression and knockout of LbGeBP1 in L. bicolor showed that LbGeBP1 negatively regulates salt gland development and salt tolerance. Further investigation revealed that the BEL1-like homeobox (BLH) LbBLH9 binds to the LbGeBP1 promoter and represses its expression. LbBLH9 was specifically expressed in salt glands. In contrast to LbGeBP1, LbBLH9 was found to positively regulate salt gland development and salt tolerance. Consistent with this regulatory relationship, silencing LbBLH9 in the LbGeBP1-overexpression background further increased LbGeBP1 expression and exacerbated defects in salt gland development and salt secretion. In contrast, simultaneous silencing of LbBLH9 and LbGeBP1 partially rescued the defects caused by silencing LbBLH9 alone. Together, these molecular and genetic data support a model in which LbBLH9 promotes salt gland development and salt tolerance by repressing the transcription of LbGeBP1. Furthermore, the LbBLH9-LbGeBP1 module regulates the expression of genes involved in salt gland development and salt stress responses. This study reveals a novel molecular mechanism governing salt gland development and salt tolerance in L. bicolor, providing a theoretical foundation for elucidating salt tolerance mechanisms in plants.