Effects of phosphate solubilization and phytohormone production of Trichoderma asperellum Q1 on promoting cucumber growth under salt stress

Salinity is one of the major abiotic stresses limiting crop growth and yield.This study investigated the underlying mechanisms of Trichoderma asperellum Q1 in promoting cucumber growth under salt stress, including the abilities of the strain to solubilize phosphate and to produce phytohormone.The results showed that T.asperellum Q1 could solubilize inorganic or organic phosphate and the activities of phosphatases and phytase could be detected in the culture supernatant.In hydroponic experiments, the growth of cucumber seedlings was increased in the hydroponic system treated by culture filtrate of strain Q1 with tricalcium phosphate or calcium phytate under salt stress.This strain also exhibited the ability to produce indole acetic acid（IAA）, gibberellic acid（GA） and abscisic acid（ABA） in liquid medium without any inducers.The levels of those three phytohormones in cucumber seedling leaves also increased after inoculated with this strain, along with increased root growth and root activities of the plant.These results demonstrated the mechanisms of T.asperellum Q1 in alleviating the suppression effect of salt stress involving the change of phytohormone levels in cucumber plant and its ability of phosphate solubilization.

耐热嗜酸β-甘露聚糖酶TaMan5A在毕赤酵母中高效表达及酶学性质研究

甘露聚糖酶是一类将甘露聚糖降解为短链甘露寡糖及甘露糖的水解酶。为了开发耐酸耐高温的工程酶,从棘孢木霉(Trichodema asperellum)ND-1中克隆甘露聚糖酶基因TaMan5A并在毕赤酵母(Komagataella phaffii)X-33中成功表达。结果显示,该酶的蛋白质分子质量约为67 kDa。最适pH值和温度分别为4.0和65℃,在pH 2.0~6.0具有较强的稳定性,孵育1 h后仍具有80%的活性,且在20~65℃时,残留酶活力均能达到90%以上。1 mmol/L Co^(2+)、脲和5 mmol/L SDS、Zn^(2+)、Fe^(2+)、Mn^(2+)、Ni^(2+)对TaMan5A的活力都有不同程度的激活作用。由于玉米秸秆富含纤维素与半纤维素,因此进一步确定了TaMan5A水解秸秆的最佳组合条件(玉米秸秆用量0.5 g,TaMan5A用量0.5 g,pH 4.0,水解2 d),并得到玉米秸秆用量和TaMan5A用量对玉米秸秆降解效率影响最大。该研究首次从棘孢木霉ND-1中克隆出TaMan5A基因,实验结果表明,TaMan5A是一种嗜酸、耐高温、热稳定性强的酶,具有较大的应用前景,值得进一步研究。