A WD40-Repeat Protein From the Recretohalophyte Limonium bicolor Enhances Trichome Formation and Salt Tolerance in Arabidopsis

Abstract

The <i>Arabidopsis thaliana</i> WD40-repeat protein <i>TRANSPARENT TESTA GLABRA1</i> (<i>TTG1</i>) controls epidermis development, playing opposite roles in trichome differentiation and root hair formation. We isolated and characterized <i>LbTTG1</i> (encoding a WD40-repeat protein with high sequence similarity to TTG1) from the recretohalophyte <i>Limonium bicolor</i>, which actively excretes absorbed salt <i>via</i> a salt gland. The complete open reading frame of <i>LbTTG1</i> was 1,095 bp, encoding a protein of 364 amino acids, and showed highest expression during the salt gland initiation stage. We heterologously expressed <i>LbTTG1</i> in wild type and <i>ttg1-13 Arabidopsis</i> plants to verify the protein's function, and the copies of LbTTG1 were identified in transgenic strains using southern blotting. Trichomes were extremely induced on the first true leaves of plants heterologously expressing <i>LbTTG1</i>, whereas no trichomes were produced by <i>ttg1-13</i> plants. Conversely, plants heterologously expressing <i>LbTTG1</i> produced fewer root hairs than <i>ttg1-13</i> plants. In plants heterologously expressing LbTTG1 compared to controls, epidermis differentiation genes (<i>GLABRA1</i> and <i>GLABRA3</i>) were up-regulated while genes encoding negative regulators of trichome development (<i>TRIPTYCHON</i> and <i>CAPRICE</i>) were down-regulated. Under increased NaCl concentrations, both of the transgenic lines showed enhanced germination and root length, and accumulated less malondialdehyde (MDA) and Na⁺ and produced more proline, soluble sugar, and higher glutathione S-transferase activity, compared with the <i>ttg1-13</i> mutant. These results indicate that LbTTG1 participates in epidermis development in <i>Arabidopsis</i>, similarly to other WD40-repeat proteins, and specifically increases salt tolerance of transgenic <i>Arabidopsis</i> by reducing ion accumulation and increasing osmolyte levels.