Bacillus circulans GN03 Alters the Microbiota, Promotes Cotton Seedling Growth and Disease Resistance, and Increases the Expression of Phytohormone Synthesis and Disease Resistance-Related Genes.

Lijun Qin,Peidong Tian,Hong Shen,Shuping Hu,Xingyong Yang,Qunyao Cui,Chengjian Xie,Wei Jian

doi:10.3389/fpls.2021.644597

Lijun Qin, Peidong Tian + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2021.644597

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Abstract

Plant growth-promoting bacteria (PGPB) are components of the plant rhizosphere that promote plant growth and/or inhibit pathogen activity. To explore the cotton seedlings response to Bacillus circulans GN03 with high efficiency of plant growth promotion and disease resistance, a pot experiment was carried out, in which inoculations levels of GN03 were set at 104 and 108 cfu⋅mL–1. The results showed that GN03 inoculation remarkably enhanced growth promotion as well as disease resistance of cotton seedlings. GN03 inoculation altered the microbiota in and around the plant roots, led to a significant accumulation of growth-related hormones (indole acetic acid, gibberellic acid, and brassinosteroid) and disease resistance-related hormones (salicylic acid and jasmonic acid) in cotton seedlings, as determined with ELISA, up-regulated the expression of phytohormone synthesis-related genes (EDS1, AOC1, BES1, and GA20ox), auxin transporter gene (Aux1), and disease-resistance genes (NPR1 and PR1). Comparative genomic analyses was performed between GN03 and four similar species, with regards to phenotype, biochemical characteristics, and gene function. This study provides valuable information for applying the PGPB alternative, GN03, as a plant growth and disease-resistance promoting fertilizer.

Highlights

In recent years, there has been considerable interest in plant growth-promoting bacteria (PGPB), which are free-living bacteria in the surrounding rhizosphere or in plant
PK3-109 and PK3-138 strains were isolated from plant root endophytes that grow in the Thar Desert, India (Bokhari et al, 2019); RIT379 strain was isolated from the internal stem tissue of Costus igneus, which grows in Puerto Rico (Polter et al, 2015); and a model strain NCTC26108
Many Plant growth-promoting bacteria (PGPB) strains are known to promote the increase of lateral roots and the formation of root hairs (Zamioudis et al, 2013; Luo et al, 2019)

Summary

Introduction

There has been considerable interest in plant growth-promoting bacteria (PGPB), which are free-living bacteria in the surrounding rhizosphere or in plant. Some studies have reported that three principal plant-associated bacteria, Bacillus cereus, Bacillus subtilis and Bacillus amyloliquefaciens, are colonizers of both the in- and outside of plant roots during the growth stage and can improve nutrient utilization, vegetative growth, flowering and fruit ripening, as well as resistance to diseases, insect pests, and environmental stress (Lugtenberg and Kamilova, 2009; Gadhave et al, 2018) These studies did not examine the impact of these bacteria on the rhizosphere and endophytic microflora (Qiao et al, 2017); there remains a disconnect between the theoretical research and the practical application of PGPB (Ramakrishna et al, 2019; Alka et al, 2020). The potential application of Bacillus in the production of a few crops, such as soybean, wheat, and rice (Khatri et al, 2020; Lee et al, 2020; Wang et al, 2020), and its effects on the growth promotion and disease resistance enhancement of upland cotton (Gossypium hirsutum L.) are rarely reported

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