A highly efficient Agrobacterium-mediated transformation system has been established for Limonium bicolor, a recretohalophyte that can actively excrete absorbed salt to the outside via a salt gland ( Ding et al., 2010 Deng et al., 2015). Two key points of focus should be identifying suitable halophytes and choosing key salt-tolerance genes. Halophytes that survive and complete their life cycles in environments with ≥200 mM NaCl can provide a broad bank of genes for improving the salt tolerance of non-halophytes. Thus, it is necessary to improve the salt tolerance of non-halophytic plants by transforming them with genes conferring salt tolerance ( Yuan et al., 2015). Few crops can survive in salt-affected regions, which leads to substantially reduced production and often results in soil degradation and desertification ( Flowers and Colmer, 2008 Song and Wang, 2015). Finding ways to make use of large areas of saline land is urgent as a means to expand available arable land ( Song et al., 2017).
Currently, 800 million hectares of land is affected by elevated salinity, and poorly designed irrigation approaches are causing rapid expansion of saline farmland worldwide ( Munns and Tester, 2008). Soil salinization inhibits the growth and production of crops worldwide. These results indicate that LbTTG1 participates in epidermis development in Arabidopsis, similarly to other WD40-repeat proteins, and specifically increases salt tolerance of transgenic Arabidopsis by reducing ion accumulation and increasing osmolyte levels. 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 ttg1-13 mutant. In plants heterologously expressing LbTTG1 compared to controls, epidermis differentiation genes ( GLABRA1 and GLABRA3) were up-regulated while genes encoding negative regulators of trichome development ( TRIPTYCHON and CAPRICE) were down-regulated. Conversely, plants heterologously expressing LbTTG1 produced fewer root hairs than ttg1-13 plants. Trichomes were extremely induced on the first true leaves of plants heterologously expressing LbTTG1, whereas no trichomes were produced by ttg1-13 plants. We heterologously expressed LbTTG1 in wild type and ttg1-13 Arabidopsis plants to verify the protein’s function, and the copies of LbTTG1 were identified in transgenic strains using southern blotting. The complete open reading frame of LbTTG1 was 1,095 bp, encoding a protein of 364 amino acids, and showed highest expression during the salt gland initiation stage. We isolated and characterized LbTTG1 (encoding a WD40-repeat protein with high sequence similarity to TTG1) from the recretohalophyte Limonium bicolor, which actively excretes absorbed salt via a salt gland. The Arabidopsis thaliana WD40-repeat protein TRANSPARENT TESTA GLABRA1 ( TTG1) controls epidermis development, playing opposite roles in trichome differentiation and root hair formation. 2Maize Research Institute, Shandong Academy of Agricultural Sciences, Jinan, China.
1Shandong Provincial Key Laboratory of Plant Stress, College of Life Sciences, Shandong Normal University, Ji’nan, China.Fang Yuan 1*†, Bingying Leng 2†, Haonan Zhang 1†, Xi Wang 1, Guoliang Han 1 and Baoshan Wang 1*
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