Department of Microbiology, Daegu Catholic University School of Medicine, Daegu, Republic of Korea.
Research Institute for Agriculture and Life Sciences, Center for Food and Bioconvergence, Seoul National University, Seoul, Republic of Korea.
PLoS One. 2019 Apr 25;14(4):e0207968. doi: 10.1371/journal.pone.0207968. eCollection 2019.
YxaL is conserved within the Bacillus subtilis species complex associated with plants and soil. The mature YxaL protein contains a repeated beta-propeller domain, but the subcellular location and function of YxaL has not been determined. The gene encoding the mature YxaL protein was PCR amplified from genomic DNA of B. velezensis strain GH1-13 and used for recombinant protein production. A rabbit polyclonal antibody against the purified YxaL was generated and used for western blotting to determine the constitutive expression and secretion of YxaL. During normal culture growth of strain GH1-13, levels of the constitutively secreted YxaL were slowly rising to 100 μg L-1, and degraded with a half-life of 1.6 h in the culture medium. When the effects of YxaL on plant seed germination and seedling growth were examined, it was shown that seed treatment of Arabidopsis thaliana and rice (Oryza sativa L.) with purified YxaL at the optimal concentration of 1 mg L-1 was effective at improving the root growth of plants. Seedlings from the treated Arabidopsis seeds markedly increased transcription of a 1-aminocyclopropane-1-carboxylate synthetase marker gene (ACS11) but reduced expression of auxin- and abscisic acid-responsive marker genes (IAA1, GH3.3, and ABF4), especially when provided with exogenous auxin. Horticulture experiments showed that pepper (Capsicum annuum) seeds treated with 1 mg L-1 YxaL in a soaking solution increased shoot growth and improved tolerance to drought stress. We hypothesize that YxaL secreted from plant growth-promoting Bacillus cells has a significant impact on plant roots, with the potential to improve plant growth and stress tolerance.
YxaL 在与植物和土壤相关的枯草芽孢杆菌物种复合体中保守。成熟的 YxaL 蛋白含有一个重复的β-螺旋桨结构域，但 YxaL 的亚细胞位置和功能尚未确定。从 B. velezensis 菌株 GH1-13 的基因组 DNA 中扩增编码成熟 YxaL 蛋白的基因，并用于重组蛋白生产。针对纯化的 YxaL 产生了兔多克隆抗体，并用于 Western blot 以确定 YxaL 的组成型表达和分泌。在 GH1-13 菌株的正常培养生长过程中，组成型分泌的 YxaL 水平缓慢上升至 100 μg L-1，并在培养基中半衰期为 1.6 h 降解。当研究 YxaL 对植物种子萌发和幼苗生长的影响时，表明用 1 mg L-1 的最佳浓度纯化的 YxaL 处理拟南芥和水稻 (Oryza sativa L.) 的种子可有效改善植物的根生长。用处理过的拟南芥种子处理的幼苗明显增加了 1-氨基环丙烷-1-羧酸合酶标记基因 (ACS11) 的转录，但降低了生长素和脱落酸响应标记基因 (IAA1、GH3.3 和 ABF4) 的表达，尤其是当提供外源生长素时。园艺实验表明，在浸泡溶液中用 1 mg L-1 YxaL 处理的辣椒 (Capsicum annuum) 种子增加了茎的生长并提高了对干旱胁迫的耐受性。我们假设从植物促生芽孢杆菌细胞分泌的 YxaL 对植物根系有显著影响，有可能改善植物的生长和胁迫耐受性。
