A genome-wide association study reveals cytokinin as a major component in the root defense responses against Ralstonia solanacearum.

Alejandro Alonso-Díaz,Wolfgang Busch,Hannah M Berry,Santosh B Satbhai,Núria S Coll,Marc Valls,Ondrej Novak,Cristiana T Argueso,Roger De Pedro-Jové,Christian Göschl,Steven Spoel

doi:10.1093/jxb/eraa610

Alejandro Alonso-Díaz, Wolfgang Busch + Show 9 more

Open Access

https://doi.org/10.1093/jxb/eraa610

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Abstract

Bacterial wilt caused by the soil-borne pathogen Ralstonia solancearum is economically devastating, with no effective methods to fight the disease. This pathogen invades plants through their roots and colonizes their xylem, clogging the vasculature and causing rapid wilting. Key to preventing colonization are the early defense responses triggered in the host’s root upon infection, which remain mostly unknown. Here, we have taken advantage of a high-throughput in vitro infection system to screen natural variability associated with the root growth inhibition phenotype caused by R. solanacearum in Arabidopsis during the first hours of infection. To analyze the genetic determinants of this trait, we have performed a genome-wide association study, identifying allelic variation at several loci related to cytokinin metabolism, including genes responsible for biosynthesis and degradation of cytokinin. Further, our data clearly demonstrate that cytokinin signaling is induced early during the infection process and cytokinin contributes to immunity against R. solanacearum. This study highlights a new role for cytokinin in root immunity, paving the way for future research that will help in understanding the mechanisms underpinning root defenses.

Highlights

Plant hormones are extremely important for the regulation of the plant defense against pathogens (Pieterse et al, 2012)
To identify sequence variation in genomic regions associated with the variation of the root growth inhibition phenotype caused by the R. solanacearum root infection, we conducted genome-wide association (GWA) mapping using the Arabidopsis 250K Single nucleotide polymorphisms (SNPs) chip data (Horton et al, 2012) with a mixed model correcting for population structure (Seren et al, 2012) and the root growth data described in Supplementary Table S2
Because we were interested in the root growth responses upon R. solanacearum root infection, we focused our analysis on root growth rates

Summary

Introduction

Plant hormones are extremely important for the regulation of the plant defense against pathogens (Pieterse et al, 2012). Cytokinin has been shown to participate in defense against various plant pathogens, including fungi (Argueso et al, 2012; Gupta et al, 2020), bacteria (Choi et al, 2010; Naseem et al, 2012; Pieterse et al, 2012). Treatments with higher levels of cytokinin increase resistance of plants to these and other pathogens (Argueso et al, 2012; Babosha, 2009; Gupta et al, 2020)

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