The MYB transcription factor LbCPC of Limonium bicolor negatively regulates salt gland development and salt tolerance

Halophytes are organisms that can grow and reproduce in high-salinity environments, making them an important resource for identifying and studying salt-tolerant genes. As the acreage of saline soils increases worldwide, it is becoming more urgent to understand and exploit the mechanism(s) of salt tolerance from halophytes, with the goal of improving the salt tolerance of crops. Limonium bicolor is a halophyte in the Plumbaginaceae family that presents salt glands on its leaf epidermis that secrete excess Na+. Here, we show that the LbCPC gene encodes a protein that participates in salt gland development and salt secretion. Transgenic lines overexpressing LbCPC showed inhibited salt gland development and decreased salt gland density, whereas lines with LbCPC silenced by virus-induced gene silencing (VIGS) showed enhanced salt gland development and an increase in the number of salt glands and the amount of salt secretion by the plant, demonstrating that LbCPC has an negative effect on salt gland development of L. bicolor. We further investigated the role of LbCPC in salt tolerance by generating transgenic lines in Arabidopsis thaliana. Compared to normal wild type, transgenic Arabidopsis lines overexpressing LbCPC had fewer trichomes and more root hairs. As the NaCl concentration increased, so did the salt sensitivity of these transgenic lines, as evidenced by inhibited germination and root elongation, which may be due to lowered expression of salt-tolerance marker genes. Together, we show that LbCPC negatively regulates the development of salt glands and inhibits the production of salt glands, providing a new avenue to screen for genes promoting salt resistance.