AUTHOR=Xu Yanyu , Jiao Xiangmei , Wang Xi , Zhang Haonan , Wang Baoshan , Yuan Fang 

TITLE=Importin-β From the Recretohalophyte Limonium bicolor Enhances Salt Tolerance in Arabidopsis thaliana by Reducing Root Hair Development and Abscisic Acid Sensitivity

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.582459

DOI=10.3389/fpls.2020.582459

ISSN=1664-462X

ABSTRACT=<sec><title>Aims</title><p>To elucidate the genetics underlying salt tolerance in recretohalophytes and assess its relevance to non-halophytes, we cloned the <italic>Limonium bicolor</italic> homolog of <italic>Arabidopsis thaliana</italic> (Arabidopsis) <italic>SUPER SENSITIVE TO ABA AND DROUGHT2</italic> (<italic>AtSAD2</italic>) and named it <italic>LbSAD2</italic>, an importin-β gene associated with trichome initiation and reduced abscisic acid (ABA) sensitivity, and then we assessed the heterologously expressed <italic>LbSAD2</italic> in Arabidopsis.</p></sec><sec><title>Methods</title><p>We examined <italic>LbSAD2</italic> expression and assessed the effect of heterologous <italic>LbSAD2</italic> expression in Arabidopsis on root hair/trichome induction; the expression levels of possible related genes in trichome/root hair development; some physiological parameters involved in salt tolerance including germination rate, root length, and contents of Na<sup>+</sup>, proline, and malondialdehyde; and the response of ABA at the germination stage.</p></sec><sec><title>Results</title><p>The <italic>LbSAD2</italic> gene is highly expressed in the salt gland development stage and salt treatment, especially located in the salt gland by <italic>in situ</italic> hybridization, and the LbSAD2 protein contains some special domains compared with AtSAD2, which may suggest the involvement of LbSAD2 in salt tolerance. Compared with the <italic>SAD2/GL1</italic> mutant CS65878, which lacks trichomes, <italic>CS65878-35S:LbSAD2</italic> had higher trichome abundance but lower root hair abundance. Under 100 mM NaCl treatment, <italic>CS65878-35S:LbSAD2</italic> showed enhanced germination and root lengths; improved physiological parameters, including high proline and low contents of Na<sup>+</sup> and malondialdehyde; higher expression of the salt-tolerance genes Δ<italic>1-PYRROLINE-5-CARBOXYLATE SYNTHETASE 1</italic> (<italic>P5CS1</italic>) and <italic>GST CLASS TAU 5</italic> (<italic>GSTU5</italic>); reduced ABA sensitivity; and increased expression of the ABA signaling genes <italic>RESPONSIVE TO ABA 18</italic> (<italic>RAB18</italic>) and <italic>SNF1-RELATED PROTEIN KINASE 2</italic> (<italic>SRK2E</italic>), but not of the ABA biosynthesis gene <italic>9-CIS-EPOXYCAROTENOID DIOXYGENASE 3</italic> (<italic>NCED3</italic>).</p></sec><sec><title>Conclusion</title><p><italic>LbSAD2</italic> enhances salt tolerance in Arabidopsis by specifically reducing root hair development, Na<sup>+</sup> accumulation, and ABA sensitivity.</p></sec>