Title: Responses of highly resistant and susceptible maize to vascular puncture inoculation with Maize dwarf mosaic virus Authors
Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 2014
Publication Date: June 16, 2014
Citation: Cassone, B.J., Chen, Z., Chiera, J., Stewart, L.R., Redinbaugh, M.G. 2014. Responses of highly resistant and susceptible maize to vascular puncture inoculation with Maize dwarf mosaic virus. Physiological and Molecular Plant Pathology. 86:19-27. Interpretive Summary: Virus diseases in crops can cause substantial losses for producers. Many of the most important virus diseases in crops are caused by a group of viruses called potyviruses. In corn, disease caused by a potyvirus called Maize dwarf mosaic virus (MDMV) is controlled by breeding virus-resistance into the hybrids grown by producers. Although we've known about the genes that give resistance to MDMV for more than 20 years, we still have little understanding of how they work to limit MDMV infection in corn. Previous research indicated that MDMV could multiply in resistant corn, but it couldn't move from leaf to leaf. In this study, we wanted to identify genes that were expressed differently in resistant and susceptible corn lines. We found that at 4 to 8 days after inoculation with virus MDMV was present in all cell types of germinating corn embryos and green leaves. We examined gene expression in germinating embryos 4 days after inoculation and found almost 4,000 genes (12% of those we examined) were differentially expressed between resistant and susceptible lines, with the majority (87%) being up regulated in the resistant line. Many fewer genes, <80 total, were differentially expressed after inoculation of the resistant and susceptible lines with MDMV. Some of the differentially regulated genes have been identified in responses of plants to viruses for model systems, but others are unique to the corn/MDMV system. This description of the differential regulation of corn genes in resistant and susceptible lines will provide the basis for developing a molecular description of virus resistance in an important crop plant.
Technical Abstract: Diseases caused by potyviruses, especially Maize dwarf mosaic virus (MDMV), are controlled by breeding virus-resistance into maize (Zea mays L.) hybrids. Although resistance to MDMV has been genetically defined for more than 20 years, the mechanisms for resistance remain unclear. Previous studies suggested that MDMV replicated in and spread to groups of cells in maize leaves of the virus resistant inbred line Pa405. The goals of the current study were to compare MDMV infection and transcriptome response in Pa405 and the virus-susceptible line Oh28. Immunocytochemical analysis was used to examine MDMV distribution in germinating seed and young leaves between 2 and 8 days post inoculation (dpi). Microarray analysis was used to examine the effects of virus inoculation on gene expression in germinating kernels of Pa405 and Oh28 at 4 dpi. At 4 to 8 dpi, MDMV was present in all cell types of both embryos and leaves, including vascular cells, and discrete boundaries between virus-infected and non-infected cells were present. In contrast, MDMV was found in a higher number of Oh28 cells, and discrete boundaries were not seen. At 4 dpi, approximately 3,900 candidate genes (12% of the total) were differentially expressed between Pa405 and Oh28, with the majority (87%) being up regulated in the resistant line. There was no difference in the genomic distribution of differentially expressed genes between Pa405 and Oh28. Substantially fewer genes were differentially expressed after inoculation of the two lines with MDMV, with 30 and 39 genes being differentially regulated in the susceptible and resistant lines, respectively. Of these, only four genes were up regulated in both lines. These results indicate that MDMV can replicate in vascular tissues, and that virus infection results in few gene expression differences between resistant and susceptible plants by the time the virus moves systemically in susceptible plants at 4 dpi.