Mehrabi Rahim, Ding Shengli, Xu Jin-Rong
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, USA.
Eukaryot Cell. 2008 May;7(5):791-9. doi: 10.1128/EC.00009-08. Epub 2008 Mar 14.
Magnaporthe grisea is a model fungus for studying fungus-plant interactions. Two mitogen-activated protein (MAP) kinase genes, PMK1 and MPS1, have been implicated in regulating plant infection processes in M. grisea. However, transcription factors activated by these MAP kinases are not well studied. In this study we functionally characterized the MIG1 gene that encodes a MADS-box transcription factor homologous to Saccharomyces cerevisiae Rlm1. In yeast two-hybrid assays, MIG1 interacts with MPS1, suggesting that MIG1 may function downstream from the MPS1 pathway. The mig1 deletion mutant had a normal growth rate and formed melanized appressoria, but it was nonpathogenic and failed to infect rice leaves through wounds. Appressoria formed by the mig1 mutant developed penetration pegs and primary infectious hyphae, but further differentiation of the secondary infectious hyphae inside live plant cells was blocked. However, the mig1 mutant formed infectious hypha-like structures in heat-killed plant cells or cellophane membranes. In transformants expressing the MIG1-GFP fusion, green fluorescent protein (GFP) signals were not detectable in vegetative hyphae and conidiophores. Mig1-GFP was localized to nuclei in conidia, appressoria, and infectious hyphae. Deletion of the MADS box had no effect on the expression and localization of the MIG1-GFP fusion but eliminated its ability to complement the mig1 mutant. These results suggest that MIG1 may be required for overcoming plant defense responses and the differentiation of secondary infectious hyphae in live plant cells. The MADS-box domain is essential for the function of MIG1 but dispensable for its nuclear localization, which may be associated with the activation of MIG1 by MPS1 during conidiation and plant infection.
稻瘟病菌是研究真菌与植物相互作用的模式真菌。两个丝裂原活化蛋白（MAP）激酶基因PMK1和MPS1参与调控稻瘟病菌的植物感染过程。然而，由这些MAP激酶激活的转录因子尚未得到充分研究。在本研究中，我们对MIG1基因进行了功能鉴定，该基因编码一种与酿酒酵母Rlm1同源的MADS盒转录因子。在酵母双杂交试验中，MIG1与MPS1相互作用，表明MIG1可能在MPS1途径的下游发挥作用。mig1缺失突变体生长速率正常，能形成黑化附着胞，但无致病性，无法通过伤口感染水稻叶片。mig1突变体形成的附着胞能发育出侵入栓和初级侵染菌丝，但在活植物细胞内次级侵染菌丝的进一步分化受阻。然而，mig1突变体在热杀死的植物细胞或玻璃纸膜中形成侵染菌丝样结构。在表达MIG1-GFP融合蛋白的转化体中，营养菌丝和分生孢子梗中未检测到绿色荧光蛋白（GFP）信号。Mig1-GFP定位于分生孢子、附着胞和侵染菌丝的细胞核中。删除MADS盒对MIG1-GFP融合蛋白的表达和定位没有影响，但消除了其互补mig1突变体的能力。这些结果表明，MIG1可能是克服植物防御反应和活植物细胞中次级侵染菌丝分化所必需的。MADS盒结构域对MIG1的功能至关重要，但对其核定位并非必需，这可能与分生孢子形成和植物感染过程中MPS1对MIG1的激活有关。
