Abstract
Puccinia striiformis f. sp. tritici (Pst) is an obligate biotrophic fungus that causes the destructive wheat stripe rust disease worldwide. Due to the lack of reliable transformation and gene disruption method, knowledge about the function of Pst genes involved in pathogenesis is limited. Mitogen-activated protein kinase (MAPK) genes have been shown in a number of plant pathogenic fungi to play critical roles in regulating various infection processes. In the present study, we identified and characterized the first MAPK gene PsMAPK1 in Pst. Phylogenetic analysis indicated that PsMAPK1 is a YERK1 MAP kinase belonging to the Fus3/Kss1 class. Single nucleotide polymerphisms (SNPs) and insertion/deletion were detected in the coding region of PsMAPK1 among six Pst isolates. Real-time RT-PCR analyses revealed that PsMAPK1 expression was induced at early infection stages and peaked during haustorium formation. When expressed in Fusarium graminearum, PsMAPK1 partially rescued the map1 mutant in vegetative growth and pathogenicity. It also partially complemented the defects of the Magnaporthe oryzae pmk1 mutant in appressorium formation and plant infection. These results suggest that F. graminearum and M. oryzae can be used as surrogate systems for functional analysis of well-conserved Pst genes and PsMAPK1 may play a role in the regulation of plant penetration and infectious growth in Pst.
Highlights
In a variety of eukaryotic organisms, a family of serine/ threonine protein kinases known as the mitogen-activated protein kinases (MAPKs) play critical roles in the transduction of a variety of extracellular signals and regulation of various development and differentiation processes [1]
PsMAPK1 had the highest homology with PgMAPK (91% identity), followed by PtMAPK1 (87% identity), M. oryzae Pmk1 (75% identity) and F. graminearum Map1 (75% identity)
Phylogenetic analysis revealed that PsMAPK1 is more closely related to M. oryzae Pmk1 and F. graminearum Map1 than to MAPKs belonging to the Slt2 and Hog1 (Fig. 1)
Summary
In a variety of eukaryotic organisms, a family of serine/ threonine protein kinases known as the mitogen-activated protein kinases (MAPKs) play critical roles in the transduction of a variety of extracellular signals and regulation of various development and differentiation processes [1]. The Fus3/Kss homolog is more extensively studied than the other two MAPKs in fungal pathogens [1,5,6,7]. In the wheat scab fungus Fusarium graminearum, the map deletion mutants are female sterile, non-pathogenic, and reduced in conidiation and infectious growth [9,10]. In Ustilago maydis, Kpp (Ubc3) and Kpp are two Fus3/Kss MAPKs with overlapping functions in mating and plant infection [11,12]. The ubc3/kpp mutant is defective in pheromone responses and the formation of filamentous dikaryons and reduced in virulence. Kpp plays a more critical role in appressorial penetration than Kpp. The kpp mutant is reduced in virulence and defective in the penetration of plant cuticle [13]. In Cryptococcus neoformans, the CPK1 MAPK pathway is important for mating and haploid fruiting but dispensable for virulence [15]
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