Abstract
PsSAK1, a mitogen-activated protein (MAP) kinase from Phytophthora sojae, plays an important role in host infection and zoospore viability. However, the downstream mechanism of PsSAK1 remains unclear. In this study, the 3'-tag digital gene expression (DGE) profiling method was applied to sequence the global transcriptional sequence of PsSAK1-silenced mutants during the cysts stage and 1.5 h after inoculation onto susceptible soybean leaf tissues. Compared with the gene expression levels of the recipient P. sojae strain, several candidates of Myb family were differentially expressed (up or down) in response to the loss of PsSAK1, including of a R2R3-type Myb transcription factor, PsMYB1. qRT-PCR indicated that the transcriptional level of PsMYB1 decreased due to PsSAK1 silencing. The transcriptional level of PsMYB1 increased during sporulating hyphae, in germinated cysts, and early infection. Silencing of PsMYB1 results in three phenotypes: a) no cleavage of the cytoplasm into uninucleate zoospores or release of normal zoospores, b) direct germination of sporangia, and c) afunction in zoospore-mediated plant infection. Our data indicate that the PsMYB1 transcription factor functions downstream of MAP kinase PsSAK1 and is required for zoospore development of P. sojae.
Highlights
Oomycetes are economically important because they are destructive to crops and nursery stocks
When zoospores were released from sporangia of PsSAK1-silenced lines, they appeared as less-active, obese protoplasmic balls, and were not as bean-shaped as zoospores of P6497
Our results demonstrate that PsSAK1 elicits a robust transcriptional response, part of which is functionally important for zoospore development
Summary
Oomycetes are economically important because they are destructive to crops and nursery stocks. Examples include Phytophthora sojae (causes soybean root rot), Phytophthora infestans (causes potato late blight), and Phytophthora ramorum (causes sudden oak death). 116 pathogenic Phytophthora species are currently known or described. P. sojae is a soil-borne plant pathogen that causes soybean stem and root rot. Since its discovery in Indiana in 1948 and Ohio in 1951, Phytophthora rot has been frequently reported globally throughout most soybeangrowing regions [2]. This disease may cause plant stand losses and complete yield reductions in susceptible soybean cultivars in poorly drained fields, costing millions of dollars each year. Slowing the assault of P. sojae pathogens is important
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