Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2011
Publication Date: 6/1/2011
Citation: Jones, M.W., Boyd, E., Redinbaugh, M.G. 2011. Responses of Maize (Zea mays L.) near isogenic lines carrying Wsm1, Wsm2 and Wsm3 to three viruses in the Potyviridae. Journal of Theoretical and Applied Genetics. DOI:10.1007/s00122-011-1622-8. 123(5):729-740.
Interpretive Summary: Genes for resistance to potyviruses (among the most destructive kinds of plant viruses) in corn had been mapped in the highly resistant line Pa405, but it was not clear how or whether these genes interacted to give resistance to the different viruses or if other factors might be involved. We developed different corn lines that had combinations of three genes previously shown to be important for corn resistance to infection by a virus called Wheat streak mosaic virus (WSMV). For these 'near isogenic lines' the pieces of the chromosomes near the resistance genes were transferred to a corn line that is highly susceptible to viruses. We investigated how each of the lines responded to infection with WSMV and the potyviruses, Maize dwarf mosaic virus (MDMV) and Sugarcane mosaic virus (SCMV). Corn lines were more virus resistant in the field than in the greenhouse, indicating that the environment influences resistance. The corn lines were most resistant to WSMV > MDMV > SCMV, indicating that the virus species influenced resistance. The corn line containing the gene Wsm1 reacted differently to infection with isolates of MDMV and SCMV from the U.S. and Europe, indicating that the same virus isolated from different regions can behave differently. The gene called Wsm1 provided the most virus resistance. The other two genes provided resistance to WSMV by themselves, but not to the other two viruses. For MDMV and SCMV, these two genes 'boosted' the activity of Wsm1, suggesting there may be important interactions among the three genes that are required for resistance. Our results will be used by scientists to define molecular interactions among corn and virus genes that lead to virus resistance in this important crop. In addition, the lines developed in this study can be used by corn breeders to develop locally-adapted, virus-resistant hybrids.
Technical Abstract: Three independent genes controlling resistance to Wheat streak mosaic virus (WSMV; family Potyviridae; genus Tritimovirus) were previously identified on chromosomes six (Wsm1), three (Wsm2) and ten (Wsm3) in the resistant maize (Zea mays L.) inbred line Pa405. Near isogenic lines (NIL) carrying each of these genes were developed by introgressing 19 to 29 cM regions of the respective chromsomes into the virus-susceptible line Oh28. NIL carrying combinations of the loci and F1 progeny from crosses of the NIL to Oh28 were also developed. The responses of this germplasm to inoculation with WSMV and Ohio isolates of two potyviruses, Maize dwarf mosaic virus (MDMV-OH) and Sugarcane mosaic virus (SCMV-OH) were determined in the field and greenhouse. The percentage of symptomatic plants and symptom severity were higher in the greenhouse than in the field, and were highest for SCMV-OH and lowest for WSMV. Wsm1 alleles provided significant resistance to all three viruses, as determined by disease incidence and area under the disease progress curves (AUDPC). On their own, Wsm2 and Wsm3 provided resistance to WSMV. The two genes provided no resistance to MDMV-OH, but significantly increased resistance in plants carrying one Wsm1 allele. NIL carrying Wsm2 and Wsm3 had a similar level of resistance to SCMV-OH as the Wsm1 NIL in the field, but were similar to Oh28 in the greenhouse. Addition of Wsm2, but not Wsm3, alleles to Wsm1 alleles increased resistance to SCMV-OH. MDMV and SCMV isolates from Ohio and Europe could be differentiated by their ability to infect the NIL carrying Wsm1. An Italian MDMV isolate and the SCMV-OH both infected the Wsm1 NIL, while the MDMV-OH and Seehausen SCMV isolates could not. Our results indicate that the three genes, or closely linked loci, provide resistance to viruses in the Potyviridae, and that interactions among the genes influence the level of resistance. The ability to distinguish between isolates of MDMV and SCMV may be useful in identifying viral genes important for the resistance reaction.