Down-regulated differentially expressed genes (DEGs) in alfalfa plants from cultivar ZG9830.

<p><b>(A)</b> Venn diagram depicting a number of unique and common down-regulated DEGs between susceptible and resistant plants 24 hours after inoculation. <b>(B)</b> Functional categorization of the unique genes down-regulated genes in susceptible plants.</p

Down-regulated differentially expressed genes (DEGs) in alfalfa plants from cultivar Maverick.

<p><b>(A)</b> Venn diagram depicting the unique and common down-regulated DEGs between susceptible and resistant plants at 72 hours after inoculation. <b>(B)</b> Functional profiling of the unique genes down-regulated in susceptible Maverick plants.</p

Differentially expressed genes (DEGs) in alfalfa plants from cultivar ZG9830 in response to inoculation with <i>P</i>. <i>syringae</i> pv. <i>syringae</i> ALF3.

<p><b>(A)</b> Venn diagram depicting a number of unique and common up-regulated DEGs between susceptible and resistant plants at 24 hours after inoculation. <b>(B)</b> Functional categorization of the unique genes up-regulated in resistant plants. <b>(C)</b> Functional categorization of the unique DEGs induced in susceptible plants at 24 hai.</p

Down-regulated differentially expressed genes (DEGs) in alfalfa plants from cultivar ZG9830.

<p><b>(A)</b> Venn diagram depicting a number of unique and common down-regulated DEGs between susceptible and resistant plants 24 hours after inoculation. <b>(B)</b> Functional categorization of the unique genes down-regulated genes in susceptible plants.</p

Comparison of differentially expressed genes (DEGs) in resistant plants from Maverick and ZG9830.

<p><b>(A)</b> Venn diagram depicting the number of common DEGs between resistant plants. <b>(B)</b> Functional categorization of biological processes associated with resistance responses to <i>P</i>. <i>syringae</i> in plants from cv. Maverick and cv. ZG9830.</p

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

<div><p>Bacterial stem blight caused by <i>Pseudomonas syringae</i> pv. <i>syringae</i> is a common disease of alfalfa (<i>Medicago sativa</i> 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 <i>Xa21</i> and soybean <i>Rpg1-b</i> resistance genes, and TIR-containing <i>R</i> genes lacking both NBS and LRR domains. The suite of <i>R</i> genes up-regulated in resistant Maverick plants had an over-representation of <i>R</i> genes in the CC-NBS-LRR family including two genes for atypical CC_R domains and a putative ortholog of the Arabidopsis <i>RPM1</i> 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.</p></div

Counts of differentially expressed genes in cv. ZG9830.

<p>Counts of differentially expressed genes in cv. ZG9830.</p

Counts of differentially expressed genes in cv. Maverick.

<p>Counts of differentially expressed genes in cv. Maverick.</p

Symptoms of bacterial stem blight at 7 days after inoculation.

<p><b>(A)</b> Response of resistant plant. <b>(B)</b> Stem of resistant plant at inoculation site. <b>(C)</b> Leaf of resistant plant at site of infiltration. <b>(D)</b> Response of susceptible plant. <b>(E)</b> Stem of susceptible plant at inoculation site. <b>(F)</b> Leaf of susceptible plant at site of infiltration. Arrows indicate point of inoculation.</p

Candidate genes involved in the resistance response against PssALF3 in two alfalfa cultivars.

<p>Candidate genes involved in the resistance response against PssALF3 in two alfalfa cultivars.</p