Malmierca Mónica G, McCormick Susan P, Cardoza Rosa E, Alexander Nancy J, Monte Enrique, Gutiérrez Santiago
Area of Microbiology, Universitary School of Agricultural Engineers, University of León, Campus de Ponferrada, Avda. Astorga s/n, Ponferrada, 24400, Spain.
Bacterial Foodborne Pathogen and Mycology Unit, National Center for Agricultural Utilization Research, USDA/ARS, Peoria, IL, USA.
Environ Microbiol. 2015 Aug;17(8):2628-46. doi: 10.1111/1462-2920.12506. Epub 2014 Jun 3.
Trichothecenes are phytotoxic sesquiterpenic mycotoxins that can act as virulence factors in plant diseases. Harzianum A (HA) is a non-phytotoxic trichothecene produced by Trichoderma arundinaceum. The first step in HA biosynthesis is the conversion of farnesyl diphosphate to trichodiene (TD), a volatile organic compound (VOC), catalysed by a sesquiterpene synthase encoded by the tri5 gene. Expression of tri5 in the biocontrol strain Trichoderma harzianum CECT 2413 resulted in production of TD in parallel with a reduction of ergosterol biosynthesis and an unexpected increase in the level of squalene. Transformants expressing tri5 displayed low chitinase activity and induced expression of Botrytis cinerea BOT genes, although their total antagonistic potential against phytopathogenic fungi was not reduced. VOCs released by the tri5-transformant induced expression of tomato defence genes related to salicylic acid (SA), and TD itself strongly induced the expression of SA-responsive genes and reduced the development of lateral roots. Together, these results suggest that TD acts as a signalling VOC in the interactions of Trichoderma with plants and other microorganisms by modulating the perception of this fungus to a given environment. Moreover, the TD ability to induce systemic defences indicates that complex trichothecene structures may not be necessary for inducing such responses.
单端孢霉烯族毒素是具有植物毒性的倍半萜霉菌毒素，可在植物病害中作为致病因子。哈茨木霉A（HA）是由哈茨木霉产生的一种无植物毒性的单端孢霉烯族毒素。HA生物合成的第一步是由tri5基因编码的倍半萜合酶催化法尼基二磷酸转化为挥发性有机化合物（VOC）——单端孢霉烯（TD）。在生防菌株哈茨木霉CECT 2413中tri5的表达导致TD的产生，同时麦角甾醇生物合成减少，而角鲨烯水平意外增加。表达tri5的转化体显示出较低的几丁质酶活性，并诱导了灰葡萄孢BOT基因的表达，尽管它们对植物病原真菌的总拮抗潜力并未降低。tri5转化体释放的VOC诱导了与水杨酸（SA）相关的番茄防御基因的表达，并且TD本身强烈诱导了SA响应基因的表达并减少了侧根的发育。总之，这些结果表明，TD通过调节这种真菌对特定环境的感知，在木霉与植物和其他微生物的相互作用中作为一种信号VOC发挥作用。此外，TD诱导系统防御的能力表明，复杂的单端孢霉烯族毒素结构对于诱导此类反应可能不是必需的。
