Expression of Fusarium pseudograminearum FpNPS9 in wheat plant and its function in pathogenicity

Fusarium pseudograminearum-induced crown rot causes significant reduction to wheat production worldwide. To date, efforts to develop effective resistance to this disease have been hampered by the quantitative nature of resistance trait and a lack of understanding of the molecular pathogenesis. Non-ribosomal peptides have important roles in development, pathogenicity, and toxins in many plant pathogens, while less is known in F. pseudograminearum. In this work, we studied the expression and function of a nonribosomal peptide gene FpNPS9 in F. pseudograminearum. We determined the expression of FpNPS9 which was significantly up regulated during the infection of wheat. A deletion mutant Δfpnps9 produced in this study displayed a normal growth and conidiation phenotype, however, hyphae polar growth was obviously affected. Deoxynivalenol production in this mutant was significantly reduced and the infection of wheat coleoptiles and wheat spikelet was attenuated. The Δfpnps9 showed serious defects on the extension of infectious hyphae in plant and inhibition of roots elongation compared with the wild type. The complementation assay using a FpNPS9-GFP fusion construct fully restored the defects of the mutant. GFP signal was detected in the germinating conidia and infectious hyphae in coleoptiles of the infected plants. Interestingly, the signal was not observed when it was grown on culture medium, suggesting that the expression of FpNPS9 was regulated by an unknown host factor. This observation was supported by the result of qRT-PCR. In summary, we provided new knowledge on FpNPS9 expression in F. pseudograminearum and its function in F. pseudograminearum pathogenicity in wheat.