The transcription factor LbYABBY1 of Limonium bicolor raises salt sensitivity by repressing the LbSAD2 pathway

The recretohalophyte Limonium bicolor produces salt glands on its leaf surface and can thrive in saline soils. YABBY (YAB) family transcription factors participate in plant development and stress responses; our previous single-cell transcriptome data revealed high expression of LbYAB1 (Lb2G09016) in salt gland subclusters. Here, we confirmed the LbYAB1 expression in salt glands and leaf primordia using RNA in situ hybridization and promoter-driven GUS histological staining; moreover, LbYAB1 expression was induced under 6-benzylaminopurine treatment. We explored LbYAB1 function by generating overexpression and knockdown plants in L. bicolor. Compared with the wild-type, LbYAB1-overexpressing lines showed suppressed salt gland development, diminished salt secretion, and lower salinity tolerance; LbYAB1 knockdown plants displayed the opposite phenotypes, demonstrating that LbYAB1 is a negative regulator of salt gland development. LbYAB1 conferred greater salinity sensitivity in L. bicolor and in Arabidopsis thaliana when overexpressed. Multiple assays (a yeast two-hybrid, split-luciferase complementation and GST pull-down) supported the interaction of LbYAB1 with LbKNAT7 (Homeobox protein knotted-1-like 7), recently shown to inhibit transcription of LbSAD2, a positive regulator of salt gland development and salt tolerance. The LbYAB1-LbKNAT7 interaction enhanced the transcriptional repression of LbSAD2, thus regulating salt gland development. Our work places LbYAB1 upstream of LbSAD2 in salt gland development, providing insights into salinity tolerance genetics and paving the way for engineering salt-resistant crops, even in species lacking salt glands.