Abstract
Mitogen-activated protein kinase (MAPK) pathways are ubiquitous and evolutionarily conserved signal transduction modules directing cellular respond to a diverse array of stimuli, in the eukaryotic organisms. In this study, PlMAPK10 was identified to encode a MAPK in Peronophythora litchii, the oomycete pathogen causing litchi downy blight disease. PlMAPK10, containing a specific and highly conserved dual phosphorylation lip sequence SEY (Serine-Glutamic-Tyrosine), represents a novel group of MAPKs as previously reported. Transcriptional profiling showed that PlMAPK10 expression was up-regulated in zoospore and cyst stages. To elucidate its function, the PlMAPK10 gene was silenced by stable transformation. PlMAPK10 silence did not impair oospore production, sporangium germination, zoospore encyst, or cyst germination but hindered hyphal growth, sporulation, pathogenicity, likely due to altering laccase activity. Over all, our results indicated that a MAPK encoded by PlMAPK10 gene in P. litchii is important for pathogenic development.
Highlights
Litchi (Litchi chinensis Sonn.) is native to China with the hugest cultivated area in the world and production due to its lovely shape, beautiful color, delicious taste, and medicinal value (Jiang et al, 2006)
Extracellular laccase or peroxidase activity has been shown to contribute to fungal or oomycete pathogenicity, we further investigate any alteration in such extracellular enzymes activities in the PlMAPK10-silenced transformants, which may account for their reduced pathogenicity
Mitogen-activated protein kinase is protein kinase highly conserved in eukaryotic organisms as signal transducers (Román et al, 2007)
Summary
Litchi (Litchi chinensis Sonn.) is native to China with the hugest cultivated area in the world and production due to its lovely shape, beautiful color, delicious taste, and medicinal value (Jiang et al, 2006). A variety of external or internal signals were shown to be transduced by MAPK pathway and regulate cell growth, development, stress response, and pathogenicity, etc. Saccharomyces cerevisiae, five important cellular development events, namely sporulation, cell wall integrity, osmoregulation, sexual mating, and filamentous (pseudohyphal) growth, have been shown to be regulated respectively by five established MAPK pathways (Chen and Thorner, 2007; Vallejo and Mayinger, 2015). In the plant pathogenic oomycetes, three MAPKs/SAPKs in Phytophthora sojae, namely PsMPK1, PsMPK3 (PsSAK1) and PsMPK7, have been demonstrated essential for spore development, osmotic and oxidative stresses responses, and pathogenicity (Li et al, 2010, 2014; Gao et al, 2015). Silence of PlMAPK10 gene led to reduced mycelial growth rate, reduced sporulation, weakened pathogenicity and altered laccase activity, indicating an important function of MAPK signal pathway in oomycete pathogenicity
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