Investigating Defense Genes in Susceptible and Tolerant Inbred lines of Corn (Zea mays L.) during Infection by Clavibacter michiganensis subsp nebraskensis, the causal agent of Goss’s Wilt.

Two corn lines that are susceptible (CO447) and tolerant (CO450) to Goss’s wilt, respectively, were inoculated with Clavibacter michiganensis subsp nebraskensis (CMN) isolates possessing different levels of aggressiveness. The highly aggressive CMN isolate (CMN14-5-1) produced severe symptoms in the susceptible corn line, which started with water soaked areas, and rapidly developed into necrotic lesions. However, the same isolates produced less severe symptoms on the tolerant corn line, which exhibited chlorosis with small necrotic lesions that did not progress beyond the initial 6 days after inoculation (dai) lesion size. Similar results were observed with the less aggressive CMN isolate (DOAB232), though symptoms were less severe overall. The AUDPC of lesion length and disease severity were significantly different between the susceptible and tolerant corn lines inoculated with both CMN isolates. Subsequently, qRT-PCR analysis of 31 genes associated with plant defense was performed on plants challenged with either CMN isolate. Leaf tissue was collected over 4 times points from 0 dai – 6 dai to observe changes in gene expression patterns over time. Three genes, respiratory burst oxidase homolog protein D (rbohD), ras-related protein 7 (Rab7), and 1-deoxy-D-xylulose-5-phosphate synthase (DXS) were upregulated only in the tolerant lines; one gene, jasmonate-zim-domain protein 20 (jaz20), was upregulated only in the susceptible line. Our phenotypic and genotypic data suggests that rbohD, Rab7, and DXS may confer tolerance to CMN in corn.