Abstract: 【Objective】 The objective of this paper is to study the relationship between STK1 and appressorium development, clarify the regulation of STK1 on the glycogen and lipid accumulation, and to make a foundation for elucidation of the molecular mechanism of appressorium development of Setosphaeria turcica.【Method】The appressoria were induced with hypha tips of wild type (WT) isolate and STK1 knock-out mutant (ΔSTK1) on the hydrophobic surface of glass slide by the method of “hypha separation with slide insertion” and incubation in a petri-dish moist chamber at 22℃ and under alternative changes of 14 h lightness and 10 h darkness, to observe the course of appressrium development under the microscope at intervals of 12 h. The glycogen in mycelia and appressoria of WT andΔSTK1 on the slides were stained 48 h with I₂/KI before and after 48 h of appressorium induction, and the changes of glycogen metabolism during appressorium development were microscopically observed. The lipid in mycelia and appressoria of WT andΔSTK1 on the slides were placed in a -70℃ ultra-low temperature freezer refrigeration for 30 min before stained for 24 h with Oil Red O, and the changes of lipid metabolism during appressorium development were microscopically observed. The expression of key genes in glycogen and lipid synthesis during appressorium development was detected by real-time PCR. 【Result】The appressoria from hypha tips could be induced on the hydrophobic surface of glass slide for both WT isolate and ⊿STK1 mutant. However, the appressoria of ΔSTK1 were differentiated into several different abnormal types, which were obviously different from WT isolate. The appressorium of WT was single cell within 48 h of appressorium induction and only a few multicellular appressoria were found after 48 h of induction. Nevertheless, the twisted appressoria were found after only 24 h of appressorium induction of ΔSTK1, and some other abnormal appressorium forms, such as double-bifurcation, multi-bifurcation and “O” type, were found after 48 h of induction. After the glycogen and lipid staining in hypha and appressoria of WT and ΔSTK1, it was found that the accumulation of glycogen and lipid was equally distributed in the mycelia and appressoria of WT isolate, but there was almost no accumulation of glycogen and lipid in the appressoria of ΔSTK1. The glycogen accumulation was significantly reduced in the mycelium of ΔSTK1 and the lipid was mainly distributed in the septum parts of hyphal cells, which were significantly different from WT. The gene expression of glycogen synthase (GS) and diacylglycerol acyltransferase (DGAT) increased by 6.6% and 40.3%, respectively, after the appressoria of WT isolate were induced after 48 hours. However, the GS gene expression decreased by 9.0% and the DGAT gene expression increased by only 24.5% in the ΔSTK1 mutant.【Conclusion】The loss of STK1 function resulted in abnormal appressorium development, decreases of glycogen accumulation, uneven distribution of lipid, and a significant reduction in the expression of key genes of glycogen and lipid synthesis, indicating the accumulation of glycogen and lipid is closely related to the appressorium development of S. turcica.

Key words: Setosphaeria turcica, STK1, appressorium development, glycogen, lipid