Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Sciences, Nanjing Normal University, Jiangsu Province, China.
Plant Cell Environ. 2018 Sep;41(9):2093-2108. doi: 10.1111/pce.13170. Epub 2018 Apr 15.
Beneficial fungal and rhizobial symbioses share commonalities in phytohormones responses, especially in auxin signalling. Mutualistic fungus Phomopsis liquidambari effectively increases symbiotic efficiency of legume peanut (Arachis hypogaea L.) with another microsymbiont, bradyrhizobium, but the underlying mechanisms are not well understood. We quantified and manipulated the IAA accumulation in ternary P. liquidambari-peanut-bradyrhizobial interactions to uncover its role between distinct symbioses. We found that auxin signalling is both locally and systemically induced by the colonization of P. liquidambari with peanut and further confirmed by Arabidopsis harbouring auxin-responsive reporter, DR5:GUS, and that auxin action, including auxin transport, is required to maintain fungal symbiotic behaviours and beneficial traits of plant during the symbiosis. Complementation and action inhibition experiments reveal that auxin signalling is involved in P. liquidambari-mediated nodule development and N -fixation enhancement and symbiotic gene activation. Further analyses showed that blocking of auxin action compromised the P. liquidambari-induced nodule phenotype and physiology changes, including vascular bundle development, symbiosome and bacteroids density, and malate concentrations, while induced the accumulation of starch granules in P. liquidambari-inoculated nodules. Collectively, our study demonstrated that auxin signalling activated by P. liquidambari symbiosis is recruited by peanut for bradyrhizobial symbiosis via symbiotic signalling pathway activation and nodule carbon metabolism enhancement.
有益真菌和根瘤菌共生体在植物激素反应方面具有共同性，尤其是在生长素信号转导方面。互惠共生真菌拟茎点霉属（Phomopsis liquidambari）可有效提高豆科花生（Arachis hypogaea L.）与另一种微共生体慢生根瘤菌（Bradyrhizobium）的共生效率，但潜在机制尚不清楚。我们定量并操纵了三元拟茎点霉属-花生-慢生根瘤菌互作中的 IAA 积累，以揭示其在不同共生体中的作用。我们发现生长素信号转导被拟茎点霉属的定殖所诱导，并且在含有生长素响应报告基因 DR5:GUS 的拟南芥中得到进一步证实，并且生长素作用，包括生长素运输，对于维持真菌共生行为和植物在共生期间的有益特性是必需的。互补和作用抑制实验表明，生长素信号转导参与了拟茎点霉属介导的根瘤发育和 N 固定增强以及共生基因激活。进一步的分析表明，生长素作用的阻断削弱了拟茎点霉属诱导的根瘤表型和生理学变化，包括维管束发育、共生体和类菌体密度以及苹果酸浓度，同时在拟茎点霉属接种的根瘤中诱导淀粉粒的积累。总的来说，我们的研究表明，拟茎点霉属共生体激活的生长素信号转导通过共生信号通路的激活和根瘤碳代谢的增强被花生招募用于慢生根瘤菌共生。
