Expression of the Histidine Kinase Gene Sshk Correlates with Dimethachlone Resistance in Sclerotinia sclerotiorum

Abstract

Histidine kinases (HK) are implicated in virulence, vegetative mycelial growth, and osmotic and oxidative responses in pathogenic fungi. Our previous work showed that transcriptional levels of the group III HK gene Sshk are higher in field dimethachlone-resistant isolates of Sclerotinia sclerotiorum compared with sensitive isolates. However, it is not clear whether the overexpression of Sshk is the major mechanism for resistance to dimethachlone. In this study, we constructed Sshk silencing and overexpression vectors and assessed dimethachlone resistance levels, virulence, mycelial growth, and sensitivity to osmotic stress for the Sshk-silenced and -overexpression transformants. Overexpression of Sshk resulted in resistance to dimethachlone and increased sensitivity to various stresses and to the cell-wall-perturbing agents sodium dodecyl sulfate (SDS) and Congo red (CR). Compared with the parent isolate, Sshk-silenced transformants had reduced resistance to dimethachlone, significantly higher (P < 0.05) mycelial growth and virulence, and lower sclerotium production, and were less sensitive to various exogenous stresses such as sodium chloride. Compared with the parent sensitive isolate HLJMG1, dimethachlone resistance ratios of the three overexpression transformants ∆C101, ∆C21, and ∆C10 increased 168.1-, 189.5-, and 221.2-fold, respectively. The three overexpression transformants were more sensitive to CR and SDS than their parent isolate. These findings suggest that overexpression of Sshk is a major mechanism for dimethachlone resistance in some isolates of S. sclerotiorum, and that Sshk plays an important role in maintaining the integrity of the cell wall. Our findings reveal a novel molecular mechanism for dimethachlone resistance in plant-pathogenic fungi.