Responses of highly resistant and susceptible maize to vascular puncture inoculation with Maize dwarf mosaic virus

• Defined effects of MDMV on gene expression in resistant and susceptible maize lines.
• Limited changes in gene expression in response to virus inoculation.
• Short list of virus responsive transcripts to begin to explain resistance response.

Mechanisms for genetic resistance to diseases caused by potyviruses, especially Maize dwarf mosaic virus (MDMV), in maize (Zea mays L.) remain unclear. Previous studies indicated that MDMV can replicate in and spread to groups of cells in maize leaves of the virus resistant inbred line Pa405, but systemic movement of the virus did not occur. In this study, the responses of Pa405 and the virus-susceptible inbred line Oh28 were compared in germinating maize embryos. Four days post inoculation (dpi), MDMV was detected immunocytochemically in 45% of resistant and 19% of susceptible shoots, respectively. Systemic movement of MDMV out of inoculated leaves occurred between 2 and 4 dpi in Oh28 seedlings. Microarray analysis was used to examine the effects of MDMV inoculation on gene expression in shoots of resistant and susceptible lines at 4 dpi. Approximately 15% of transcripts were differentially expressed between the resistant and susceptible lines. Of the transcripts with >10 fold greater expression in one line, more than 70% were up-regulated in the resistant line. Substantially fewer genes were differentially expressed in MDMV- and mock-inoculated shoots, with 21 and 30 genes being differentially regulated in the susceptible and resistant lines, respectively. For a subset of genes, differential expression was validated using quantitative real-time PCR. There was no clustering of differentially expressed transcripts in the previously identified QTLs important for MDMV resistance. These results provide a short list of virus responsive transcripts to begin to explain the resistance response in Pa405 versus the susceptible response in Oh28.