StRas2 regulates morphogenesis, conidiation and appressorium development in Setosphaeria turcica

Abstract

The proteins of Ras family are a large group of monomeric GTPases and act as molecular switches transducing extracellular signals into the cell in higher eukaryotes. However, little is known about roles of Ras family in the foliar pathogens. In this research, we cloned the gene named StRas2 encoding Ras in Setosphaeria turcica and investigated its function by RNA interference technology. We found that the growth rate of RNAi transformants named as R1, R2, R3, R4, R5 and R6, in which the StRas2 silencing efficiency fell in turn. With the highest silencing efficiency, the transformant R1 showed anomalistic hyphae morphology, indicating its growth was significantly affected. The transformants with a middle-silencing efficiency, such as R3, R4, displayed a delay when forming appressoria and invasive hyphae. R1 could not form conidia and appressoria. However, the conidial formation in R5 and R6 was significantly reduced, and these two transformants could form appressoria and penetrate the artificial cellophane, only that its invasive hyphae were fascicular and rarely branched. The HT-toxin biological activity of all transformants showed no difference. All results suggested that StRas2 is involved in the morphogenesis, conidiation, and appressorium development and is not related to the biosynthesis of HT-toxin.

The catalytic subunit of cAMP-dependent protein kinase AStPKA-ccontributes to conidiation and early invasion in the phytopathogenic fungusSetosphaeria turcica

“…For DNA or RNA isolation, fungi were statically cultured in potato dextrose (PD) medium at 25°C. For protoplast preparation, conidia from the cultivated strain 01-23 were cultured in Fries medium for 24 h with shaking (Zhang et al, 2012).…”

Orchestration of morphogenesis in filamentous fungi: conserved roles for Ras signaling networks

“…Transformants with the greatest amount of StRas2 suppression display a stunted hyphal phenotype, polarity maintenance defects and reduced conidiation (Zhang et al, 2012b). Exogenous cAMP does not abrogate the aberrant hyphal phenotype but does partially resolve the conidiation defect caused by StRas2 suppression.…”

“…StRas2 suppression is also associated with loss of appressorium development, reduced appressorial turgur pressure, and reduced pathogenicity. Exogenous cAMP again could not remediate the defects in appressorium development (Zhang et al, 2012b). Therefore, StRas2 may signal through the cAMP/PKA pathway for asexual development but controls hyphal morphogenesis and virulence through cAMP-independent mechanisms.…”

Setosphaeria turcica ATR turns off appressorium‐mediated maize infection and triggers melanin‐involved self‐protection in response to genotoxic stress

“…In previous work, we demonstrated that appressorium-mediated infection is regulated by the cyclic AMP and mitogen activated protein kinase signalling pathways under suitable conditions in S. turcica, which indicates a positive interaction between environmental signals and appressorium development (Zhang et al, 2012;Shen et al, 2013;Gu et al, 2014). However, phytopathogenic fungi are frequently challenged by environmental genotoxic stresses that cause DNA damage or interfere with DNA replication.…”

“…NCLB is a serious fungal foliar disease of cultivated maize that causes devastating loss of yield and a reduction in feed value (Van Inghelandt et al , ). S. turcica develops a specialized cell, called an appressorium, to infect leaves during the pathogen infection cycle (Zhang et al , ; Gu et al , ). S. turcica has emerged as a significant global maize foliar pathogen and causal agent of NCLB, but the regulation of appressorium‐mediated infection remains largely unknown.…”