Non-rhizobial endophytic (NRE) yeasts assist nodulation of Rhizobium in root nodules of blackgram ( Vigna mungo L.)
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ORIGINAL PAPER
Non‑rhizobial endophytic (NRE) yeasts assist nodulation of Rhizobium in root nodules of blackgram (Vigna mungo L.) Kalyanasundaram Geetha Thanuja1 · Brundha Annadurai1 · Sugitha Thankappan1 · Sivakumar Uthandi1 Received: 6 April 2020 / Revised: 25 June 2020 / Accepted: 14 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The signal orchestration between legumes and the rhizobia attribute to symbiotic nitrogen fixation through nodule formation. Root nodules serve as a nutrient-rich reservoir and harbor diverse microbial communities. However, the existence of nonrhizobial endophytes (NRE) and their role inside the root nodules are being explored; there is no evidence on yeast microflora inhabiting nodule niche. This study focused on unraveling the presence of yeast in the root nodules and their possible function in either nodulation or signal exchange. From the root nodules of blackgram, two yeast strains were isolated and identified as Candida glabrata VYP1 and Candida tropicalis VYW1 based on 18S rRNA gene sequencing and phylogeny. These strains possessed plant growth-promoting traits viz., IAA, ACC deaminase, siderophore, ammonia, and polyamine production. The functional capacity of endophytic yeast strains, and their interaction with Rhizobium sp. was further unveiled via profiling volatile organic compounds (VOC). Among the VOCs, α-glucopyranoside and pyrroloquinoline pitches a pivotal role in activating lectin pathways and phosphorous metabolism. Further, lectin pathways are crucial for nodulating bacterium, and our study showed that these endophytic yeasts assist nodulation by Rhizobium sp. via activating the nod factors. The plant growth-promoting traits of NRE yeast strains coupled with their metabolite production, could recruit them as potential drivers in the plant–microbe interaction. Keywords Non-rhizobial endophytes · Rhizobium · Yeasts · Volatiles · Root nodules
Introduction Leguminosae ranks third largest family among the angiosperms, comprising nearly 20,000 species and 750 genera. Most of them have the potential to establish a symbiotic relation with diazotrophic bacteria, Rhizobium sp. (Peix et al. 2015). This symbiosis is a crucial interaction renowned for agricultural importance of biological nitrogen fixation (BNF), leading to crop productivity. The beneficial association has put forward the interest in root nodules, which execute nitrogen fixation. Root nodules, besides admitting Rhizobium, also accommodate several non-nodulating endophytes, which have a definite influence on either the host physiological process or Communicated by Erko Stackebrandt. * Sivakumar Uthandi [email protected] 1
Biocatalysts Laboratory, Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu 641003, India
nodulation. Agrobacterium radiobacter was the first isolated non-nodulating bacterium from the nodules of a leguminous plant (Beiierinck and Van Delden 1902). The succeeding isolation of non-rhizobial bacteria a
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