Resistant and susceptible responses in alfalfa (Medicago sativa) to bacterial stem blight caused by Pseudomonas syringae pv. syringae

Abstract

Bacterial stem blight caused by Pseudomonas syringae pv. syringae is a common disease of alfalfa (Medicago sativa L). Little is known about host-pathogen interactions and host defense mechanisms. Here, individual resistant and susceptible plants were selected from cultivars Maverick and ZG9830 and used for transcript profiling at 24 and 72 hours after inoculation (hai) with the isolate PssALF3. Bioinformatic analysis revealed a number of differentially expressed genes (DEGs) in resistant and susceptible genotypes. Although resistant plants from each cultivar produced a hypersensitive response, transcriptome analyses indicated that they respond differently at the molecular level. The number of DEGs was higher in resistant plants of ZG9830 at 24 hai than in Maverick, suggesting that ZG9830 plants had a more rapid effector triggered immune response. Unique up-regulated genes in resistant ZG9830 plants included genes encoding putative nematode resistance HSPRO2-like proteins, orthologs for the rice Xa21 and soybean Rpg1-b resistance genes, and TIR-containing R genes lacking both NBS and LRR domains. The suite of R genes up-regulated in resistant Maverick plants had an over-representation of R genes in the CC-NBS-LRR family including two genes for atypical CCR domains and a putative ortholog of the Arabidopsis RPM1 gene. Resistance in both cultivars appears to be mediated primarily by WRKY family transcription factors and expression of genes involved in protein phosphorylation, regulation of transcription, defense response including synthesis of isoflavonoids, and oxidation-reduction processes. These results will further the identification of mechanisms involved in resistance to facilitate selection of parent populations and development of commercial varieties.

Cellular and Transcriptional Responses of Resistant and Susceptible Cultivars of Alfalfa to the Root Lesion Nematode, Pratylenchus penetrans

“…Since the presence of nematode RNA was low, the RPKM (Reads Per Kilobase Per Million) value was calculated for each DETs. The Blast2GO tool was used for functional categorization of DETs (Gotz et al, 2008) as previously described (Nemchinov et al, 2017). The distribution scores in the Gene Ontology (GO) charts represent the sum of sequences directly or indirectly associated to a given GO category weighted by the distance of the category to the term of “direct annotation” (User Manual, Blast2Go 7 ).…”

High-Throughput Sequencing for Deciphering the Virome of Alfalfa (Medicago sativa L.)

“…The RNA-seq data in which the virus reads were identified originated from the publicly available datasets SRR6050922 to SRR6050957 generated from the U.S. alfalfa cultivars Maverick and ZG9830 ( Nemchinov et al, 2017c ). The subject of the original study was not related to virology research, and these datasets were evaluated a second time as part of an effort to identify emerging viral genomes in publicly available alfalfa transcriptomic repositories.…”

Genomics of Plant Disease Resistance in Legumes

“…syringae causes bacterial stem blight in alfalfa. RNAseq was conducted to study the host–pathogen interactions in resistant and susceptible alfalfa cultivars at two different time points (Nemchinov et al, 2017). The timing of resistance response differed in both cultivars.…”