Jiao Jian, Ma Yaner, Chen Sha, Liu Chonghuai, Song Yuyang, Qin Yi, Yuan Chunlong, Liu Yanlin
College of Enology, Northwest A&F University Yangling, China.
Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
Front Plant Sci. 2016 Sep 21;7:1387. doi: 10.3389/fpls.2016.01387. eCollection 2016.
Endophytes form symbiotic relationships with plants and constitute an important source of phytohormones and bioactive secondary metabolites for their hosts. To date, most studies of endophytes have focused on the influence of these microorganisms on plant growth and physiology and their role in plant defenses against biotic and abiotic stressors; however, to the best of our knowledge, the ability of endophytes to produce melatonin has not been reported. In the present study, we isolated and identified root-dwelling bacteria from three grapevine varieties and found that, when cultured under laboratory conditions, some of the bacteria strains secreted melatonin and tryptophan-ethyl ester. The endophytic bacterium SB-9 exhibited the highest level of melatonin secretion and also produced three intermediates of the melatonin biosynthesis pathway: 5-hydroxytryptophan, serotonin, and -acetylserotonin. After SB-9 colonization, the plantlets exhibited increased plant growth. Additionally, we found that, in grapevine plantlets exposed to salt or drought stress, colonization by SB-9 increased the upregulation of melatonin synthesis, as well as that of its intermediates, but reduced the upregulation of grapevine tryptophan decarboxylase genes (s) and a serotonin -acetyltransferase gene () transcription, when compared to the un-inoculated control. Colonization by SB-9 was also able to counteract the adverse effects of salt- and drought-induced stress by reducing the production of malondialdehyde and reactive oxygen species (HO and O) in roots. Therefore, our findings demonstrate the occurrence of melatonin biosynthesis in endophytic bacteria and provide evidence for a novel form of communication between beneficial endophytes and host plants melatonin.
内生菌与植物形成共生关系，是其宿主植物激素和生物活性次生代谢产物的重要来源。迄今为止，大多数关于内生菌的研究都集中在这些微生物对植物生长和生理的影响以及它们在植物抵御生物和非生物胁迫中的作用；然而，据我们所知，尚未有关于内生菌产生褪黑素能力的报道。在本研究中，我们从三个葡萄品种中分离并鉴定了根际细菌，发现当在实验室条件下培养时，一些细菌菌株会分泌褪黑素和色氨酸乙酯。内生细菌SB - 9表现出最高水平的褪黑素分泌，并且还产生了褪黑素生物合成途径的三种中间体：5 - 羟色氨酸、血清素和N - 乙酰血清素。SB - 9定殖后，幼苗的植物生长有所增加。此外，我们发现，在暴露于盐或干旱胁迫的葡萄幼苗中，与未接种的对照相比，SB - 9的定殖增加了褪黑素及其中间体合成的上调，但降低了葡萄色氨酸脱羧酶基因和血清素N - 乙酰转移酶基因转录的上调。SB - 9的定殖还能够通过减少根中丙二醛和活性氧（H₂O₂和O₂）的产生来抵消盐和干旱诱导胁迫的不利影响。因此，我们的研究结果证明了内生细菌中存在褪黑素生物合成，并为有益内生菌与宿主植物之间一种新的通讯形式——褪黑素提供了证据。
