Functional Analyses Of A MAPK Homolog Gene PsMAPK From Wheat Stripe Rust Puccinia Striiformis F.SP. Tritici

Wheat stripe rust disease, caused by Puccinia striiformis f.sp. tritici, is one of the most serious wheat diseases worldwide. The pathogen can spread rapidly to large areas during the epidemic year, thus causes serious production loss to wheat. Identifying pathogenicity related genes is of great significance for understanding the mechanism of its infection and controlling it. However, the molecular study of wheat stripe rust has been severely hampered by lacking of efficient transformation system caused by the obligate nature.Mitogen-activated protein kinases (MAPK), are serine/threonine-specific protein kinases that respond to extracellular stimuli and widely exist in eukaryotic cells. They play important roles in regulating growth, differentiation and pathogenity and other activities in fungi. The MAPK cascades are well studied in Fusarium graminearu, and the gene deletion mutants are available. In this research a PsMAPK gene was isolated from Puccinia striiformis, and its function was analyzed in the deletion mutant of its homologous gene in F. graminearu.The main results are listed as follows:The protein encoded by PsMAPK contains 480 aa, and has the MAPK conserved site, Serine/threonine-protein kinase domain, and ATP biding site.The relative expression levels of the PsMAPK gene in different stages including spore, germ tube, infection, invasive growth and sporulation was analyzed by real time RT-PCR. The result showed that the expression of the PsMAPK gene in the germed urediospore massively increased compared with the level in spore, with a 20 fold increase; the first expression peak appeared 24 hpi, which was two-fold than the germination stage. After that the expression reduced slowly to a level 10 fold higher than spore. PsMAPK gene may function in multiple stages in its pathogenicity process such as germ tube, infection and sporulation.Expression of the PsMAPK-ORF in mgv1 mutant of F. graminearu did not restore the slow growth rate of the mutant on CM medium and the inability of the mutant to produce perithecium, however the infection it could partially restore the mutant's inability to produce disease syndrome in wheat spike. The complement strain could infect wheat spike, although the mycelium produced could not expand after inoculate.