Foliar Application or Seed Priming of Cholic Acid-Glycine Conjugates can Mitigate/Prevent the Rice Bacterial Leaf Blight Disease via Activating Plant Defense Genes.

Garima Pal,Saurabh Singh,Kalai Magal,Siddhi Gupta,Devashish Mehta,Avinash Bajaj,Vemanna S Ramu,Gopaljee Jha

doi:10.3389/fpls.2021.746912

Abstract

Xanthomonas Oryzae pv. oryzae (Xoo) causes bacterial blight and Rhizoctonia solani (R. solani) causes sheath blight in rice accounting for >75% of crop losses. Therefore, there is an urgent need to develop strategies for the mitigation of these pathogen infections. In this study, we report the antimicrobial efficacy of Cholic Acid-Glycine Conjugates (CAGCs) against Xoo and R. solani. We show that CAGC C6 is a broad-spectrum antimicrobial and is also able to degrade biofilms. The application of C6 did not hamper plant growth and showed minimal effect on the plant cell membranes. Exogenous application of C6 on pre-infection or post-infection of Xoo on rice susceptible genotype Taichung native (TN1) can mitigate the bacterial load and improve resistance through upregulation of plant defense genes. We further demonstrate that C6 can induce plant defense responses when seeds were primed with C6 CAGC. Therefore, this study demonstrates the potential of CAGCs as effective antimicrobials for crop protection that can be further explored for field applications.

Highlights

Sessile rice plants are always vulnerable to the pathogens, such as bacteria, fungi, and viruses that can lead to >25% of crop losses
We used nine Cholic Acid-Glycine Conjugates (CAGCs), where Cholic acid (CA) was modified at the carboxylic acid position with different alkyl groups using ester bonds, and three glycine moieties were tethered at three hydroxyl groups (Figure 1A) (Yadav et al, 2019)
The growth kinetics at 8 and 16 μg/ml showed that C4, C5, and C6 CAGCs are the most effective antibacterial against Xanthomonas oryzae pv. oryzae (Xoo) as they reduced the multiplication at 8 μg/ml, and complete growth inhibition at 16 μg/ml (Figures 1B, C)

Summary

Introduction

Sessile rice plants are always vulnerable to the pathogens, such as bacteria, fungi, and viruses that can lead to >25% of crop losses. Rice bacterial blight caused by Xanthomonas oryzae pv. Oryzae (Xoo) is one of the devastating diseases that can severely cause yield losses depending on the variety, growth stage, and environmental conditions (Liu et al, 2014; Varshney et al, 2019). Xoo is a Gram-negative bacterium that enters into the rice plants through hydathodes or wounds of leaf-tip. Xoo infection causes water-soaked spots at leaf tips and margins that later become chlorotic and necrotic lesions on leaf veins. Xoo can infect the rice at the seedling stage called kresek and can result in partial or even complete crop loss. Rice sheath blight caused by soil-borne necrotrophic

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