Identification of Genes in a Partially Resistant Genotype of Avena sativa Expressed in Response to Puccinia coronata Infection.

Yolanda Loarce,Elisa Navas,José L Manjón,Esther Ferrer,Araceli Fominaya,Carlos Paniagua

doi:10.3389/fpls.2016.00731

Abstract

Cultivated oat (Avena sativa), an important crop in many countries, can suffer significant losses through infection by the fungus Puccinia coronata, the causal agent of crown rust disease. Understanding the molecular basis of existing partial resistance to this disease might provide targets of interest for crop improvement programs. A suppressive subtractive hybridization (SSH) library was constructed using cDNA from the partially resistant oat genotype MN841801-1 after inoculation with the pathogen. A total of 929 genes returned a BLASTx hit and were annotated under different GO terms, including 139 genes previously described as participants in mechanisms related to the defense response and signal transduction. Among these were genes involved in pathogen recognition, cell-wall modification, oxidative burst/ROS scavenging, and abscisic acid biosynthesis, as well genes related to inducible defense responses mediated by salicylic and jasmonic acid (although none of which had been previously reported involved in strong responses). These findings support the hypothesis that basal defense mechanisms are the main systems operating in oat partial resistance to P. coronata. When the expression profiles of 20 selected genes were examined at different times following inoculation with the pathogen, the partially resistant genotype was much quicker in mounting a response than a susceptible genotype. Additionally, a number of genes not previously described in oat transcriptomes were identified in this work, increasing our molecular knowledge of this crop.

Highlights

Crown rust, caused by the obligate fungal biotroph Puccinia coronata Corda. f. sp. avenae Eriks, is a widespread destructive disease of cultivated oat (Avena sativa L.) and infections may cause considerable losses in yield and important reductions in grain quality (Gnanesh et al, 2015)
Sequence Analysis suppressive subtractive hybridization (SSH) was used to identify the oat genes induced by P. coronata. cDNA from inoculated oat leaves was used as the tester, and cDNA from non-inoculated control oat leaves as the driver
This indicates that duplicates (i.e., >95% similarity for >97% of the sequence length) corresponding to either splice variants, sequences belonging to the different subgenomes of the hexaploid oat, or sequences belonging to highly related multigene families, clustered separately in the assembly process

Summary

Introduction

Crown rust, caused by the obligate fungal biotroph Puccinia coronata Corda. f. sp. avenae Eriks, is a widespread destructive disease of cultivated oat (Avena sativa L.) and infections may cause considerable losses in yield and important reductions in grain quality (Gnanesh et al, 2015). Many P. coronata populations have adapted to these resistance genes, resulting in the emergence of new, virulent races of the pathogen. These once-resistant cultivars have become susceptible to the disease (McCallum et al, 2007). Partial resistance (PR) is a type of incomplete resistance, frequently under polygenic control In oat it is expressed only in adult plants but is believed to have broad-spectrum effectiveness against all physiological races of P. coronata. In other species this form of resistance has been selected and used to provide a layer of resistance in the absence of monogenic-mediated resistance (Poland et al, 2008). PR can provide protection even when cultivars are grown for prolonged periods in environments favorable to the spread of crown rust (Leonard, 2002)

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