Platform of hot pepper defense genomics: isolation of pathogen responsive genes in hot pepper (Capsicum annuum L.) non-host resistance against soybean pustule pathogen (Xanthomonas axonopodis pv. glycines)

Abstract

Host resistance is usually parasite-specific and isrestricted to a particular pathogen races, and common-ly is expressed against specific pathogen genotypes. Incontrast, resistance shown by an entire plant species to aspecies of pathogen is known as non-host resistance.Therefore, non-host resistance is the more common andbroad form of disease resistance exhibited by plants. Asa first step to understand the mechanism of non-hostplant defense, expressed sequence tags (EST) weregenerated from a hot pepper leaf cDNA libraryconstructed from combined leaves collected at differenttime points after inoculation with non-host soybeanpustule pathogen (Xanthomonas axonopodis pv. Glycines;Xag). To increase gene diversity, ESTs were alsogenerated from cDNA libraries constructed from anthersand flower buds. Among a total of 10,061 ESTs, 8,525were of sufficient quality to analyze further. Clusteringanalysis revealed that 55% of all ESTs (4685) occurredonly once. BLASTX analysis revealed that 74% of theESTs had significant sequence similarity to knownproteins present in the NCBI nr database. In addition,1,265 ESTs were tentatively identified as being full-length cDNAs. Functional classification of the ESTsderived from pathogen-infected pepper leaves revealedthat about 25% were disease- or defense-related genes.Furthermore, 323 (7%) ESTs were tentatively identifiedas being unique to hot pepper. This study represents thefirst analysis of sequence data from the hot pepper plantspecies. Although we focused on genes related to theplant defense response, our data will be useful for futurecomparative studies