Gansu Provincial Key Laboratory of Arid Land Crop Science, Gansu Agricultural University/College of Plant protection, Gansu Agricultural University/ Biocontrol Engineering Laboratory of Crop Diseases and Pests of Gansu Province, Lanzhou, 730070, China.
Agriculture and Agri-Food Canada/Government of Canada Swift Current Research & Development Centre, Swift Current, Saskatchewan, SK S9H 3X2, Canada.
BMC Plant Biol. 2019 Jan 11;19(1):22. doi: 10.1186/s12870-018-1618-5.
Trichoderma species, a class of plant beneficial fungi, may provide opportunistic symbionts to induce plant tolerance to abiotic stresses. Here, we determined the possible mechanisms responsible for the indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate-deaminase (ACC-deaminase) producing strain of Trichoderma longibrachiatum T6 (TL-6) in promoting wheat (Triticum aestivum L.) growth and enhancing plant tolerance to NaCl stress.
Wheat treated with or without TL-6 was grown under different levels of salt stress in controlled environmental conditions. TL-6 showed a high level of tolerance to 10 mg ml of NaCl stress and the inhibitory effect was more pronounced at higher NaCl concentrations. Under NaCl stress, the activity of ACC-deaminase and IAA concentration in TL-6 were promoted, with the activity of ACC-deaminase increased by 26% at the salt concentration of 10 mg ml and 31% at 20 mg ml, compared with non-saline stress; and the concentration of IAA was increased by 10 and 7%, respectively (P < 0.05). The increased ACC-deaminase and IAA concentration in the TL-6 strain may serve as an important signal to alleviate the negative effect of NaCl stress on wheat growth. As such, wheat seedlings with the ACC-deaminase and IAA producing strain of TL-6 treatment under NaCl stress increased the IAA concentration by an average of 11%, decreased the activity of ACC oxidase (ACO) by an average of 12% and ACC synthase (ACS) 13%, and decreased the level of ethylene synthesis and the content of ACC by 12 and 22%, respectively (P < 0.05). The TL-6 treatment decreased the transcriptional level of ethylene synthesis genes expression, and increased the IAA production genes expression significantly in wheat seedlings roots; down-regulated the expression of ACO genes by an average of 9% and ACS genes 12%, whereas up-regulated the expression of IAA genes by 10% (P < 0.05). TL-6 treatments under NaCl stress decreased the level of Na accumulation; and increased the uptake of K and the ratio of K/Na, and the transcriptional level of Na/H antiporter gene expression in both shoots and roots.
Our results indicate that the strain of TL-6 effectively promoted wheat growth and enhanced plant tolerance to NaCl stress through the increased ACC-deaminase activity and IAA production in TL-6 stain that modulate the IAA and ethylene synthesis, and regulate the transcriptional levels of IAA and ethylene synthesis genes expression in wheat seedling roots under salt stress, and minimize ionic toxicity by disturbing the intracellular ionic homeostasis in the plant cells. These biochemical, physiological and molecular responses helped promote the wheat seedling growth and enhanced plant tolerance to salt stress.
木霉属真菌是一类有益的植物真菌，它们可能作为机会共生体诱导植物耐受非生物胁迫。在这里，我们确定了长枝木霉 T6（TL-6）产生吲哚乙酸（IAA）和 1-氨基环丙烷-1-羧酸脱氨酶（ACC-脱氨酶）菌株促进小麦（Triticum aestivum L.）生长和增强植物耐盐胁迫的可能机制。
在控制环境条件下，用或不用 TL-6 处理的小麦在不同水平的盐胁迫下生长。TL-6 对 10mg/ml 的 NaCl 胁迫具有较高的耐受性，在较高的 NaCl 浓度下抑制作用更为明显。在盐胁迫下，TL-6 中的 ACC-脱氨酶活性和 IAA 浓度增加，在盐浓度为 10mg/ml 和 20mg/ml 时，ACC-脱氨酶活性分别增加了 26%和 31%；IAA 浓度分别增加了 10%和 7%（P<0.05）。TL-6 菌株中 ACC-脱氨酶和 IAA 浓度的增加可能是缓解 NaCl 胁迫对小麦生长负面影响的重要信号。因此，在 NaCl 胁迫下，用 ACC-脱氨酶和 IAA 产生菌株 TL-6 处理的小麦幼苗中 IAA 浓度平均增加了 11%，ACC 氧化酶（ACO）活性平均降低了 12%，ACC 合成酶（ACS）降低了 13%，乙烯合成和 ACC 含量分别降低了 12%和 22%（P<0.05）。TL-6 处理降低了小麦幼苗根中乙烯合成基因表达的转录水平，显著增加了 IAA 产生基因的表达；ACO 基因表达平均下调 9%，ACS 基因表达下调 12%，而 IAA 基因表达上调 10%（P<0.05）。TL-6 在 NaCl 胁迫下处理降低了 Na 积累水平；增加了 K 的摄取和 K/Na 比值，并上调了根和地上部 Na/H 反向转运蛋白基因表达的转录水平。
我们的结果表明，TL-6 菌株通过增加 TL-6 菌株中的 ACC-脱氨酶活性和 IAA 产生，调节 IAA 和乙烯合成，调节盐胁迫下小麦幼苗根中 IAA 和乙烯合成基因表达的转录水平，以及通过干扰植物细胞内离子稳态，减轻离子毒性，从而有效促进小麦生长，增强植物耐盐胁迫能力。这些生化、生理和分子反应有助于促进小麦幼苗的生长，增强植物对盐胁迫的耐受性。
