Abstract
The devastating fungus Magnaporthe oryzae (M. oryzae) forms a specialized infection structure known as appressorium, which generates enormous turgor, to penetrate the plant cells. However, how M. oryzae regulates the appressorium turgor formation, is not well understood. In this study, we identified MoBZIP3, a bZIP transcription factor that functioned in pathogenesis in M. oryzae. We found that the pathogenicity of the MoBZIP3 knockout strain (Δmobzip3) was significantly reduced, and the defect was restored after re-expression of MoBZIP3, indicating that MoBZIP3 is required for M. oryzae virulence. Further analysis showed that MoBZIP3 functions in utilization of glycogen and lipid droplets for generation of glycerol in appressorium. MoBZIP3 localized in the nucleus and could bind directly to the promoters of the glycerol synthesis-related genes, MoPTH2, MoTGL1 and MoPEX6, and regulate their expression which is critical for glycerol synthesis in the appressorium turgor pressure generation. Furthermore, the critical turgor sensor gene MoSln1 was also down regulated and its subcellular localization was aberrant in Δmobzip3, which leads to a disordered actin assembly in the Δmobzip3 appressorium. Taken together, these results revealed new regulatory functions of the bZIP transcription factor MoBZIP3, in regulating M. oryzae appressorium turgor formation and infection.
Highlights
Rice blast disease caused by the devastating fungus Magnaporthe oryzae (M. oryzae) is the greatest threat to the global rice harvest and leads to serious economic losses worldwide every year [1]
Since the differentiation of infection structures is without exogenous nutrients, it underlines the fact that appressorium development is nutrified by compounds transferred from the conidia
Previous work has shown that knockout of MoBZIP3 in strain Guy11 and KJ201 did not result in significant changes in the M. oryzae development and virulence
Summary
Rice blast disease caused by the devastating fungus Magnaporthe oryzae (M. oryzae) is the greatest threat to the global rice harvest and leads to serious economic losses worldwide every year [1]. Transcription factors generally include the BZIP proteins, MYB-like proteins, MADSbox proteins, helix-loop-helix proteins, zinc-finger proteins, and homeobox proteins [10] They could bind to specific promoter sequences to regulate expression of the target genes and function as key regulatory elements in the control of gene expression in development and plant infection in fungi [11]. In M. oryzae, over twenty members of BZIP proteins are encoded in the genome, and the members such as MoAP1, MoBZIP13, MoBZIP22, MoMetR, MoBZIP5 and MoMeaB were shown to play critical roles in M. oryzae sporation, appressiorium formation or host infection [15,16,17]. The expression of MoSln was reduced and the protein subcellular localization was changed in ∆mobzip3 These resulted in an abnormal assembly of actin ring in the specialized cell which is critical for the host penetration of M. oryzae. We demonstrated the biological functions of the bZIP protein in regulation of both glycerol synthesis and MoSln mediated-turgor sensing in appressorium
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