LbNAC55 improves the salt tolerance of Limonium bicolor by regulating the salt gland development

The NAC transcription factors (TFs) are among the largest TF families in plants and play essential roles in growth, development, and stress responses. However, few studies have investigated how NAC TFs regulate salt gland development of recretohalophytes. In this study, we identified LbNAC55, a TF whose expression is upregulated by salt, from Limonium bicolor (a typical recretohalophyte which serves as a model for studying development and salt secretion of plant salt glands). Overexpression of LbNAC55 in L. bicolor significantly increases salt gland density and the salt tolerance of the species, whereas silencing LbNAC55 results in reduced salt gland development and diminished salt tolerance. Furthermore, yeast two-hybrid screening revealed that LbFLZ13 interacts with LbNAC55. Silencing LbFLZ13 similarly decreased salt gland formation and salt tolerance. Further studies showed that the reduction in salt gland density induced by the simultaneous silencing of both LbNAC55 and LbFLZ13 was significantly lower than that caused by the silencing of either gene alone. These results demonstrate that the regulatory modules of LbNAC55-LbFLZ13 control the expression of genes involved in salt gland development and secretion. These findings provide a new perspective on salt gland development in halophytes.