Homeobox transcription factors are required for conidiation and appressorium development in the rice blast fungus Magnaporthe oryzae.
Homeobox transcription factors are required for conidiation and appressorium development in the rice blast fungus Magnaporthe oryzae.
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DOI：
10.1371/journal.pgen.1000757
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发表时间：
2009-12
期刊：
影响因子：
4.5
通讯作者：
Lee YH
中科院分区：
文献类型：
--
作者：
Kim S;Park SY;Kim KS;Rho HS;Chi MH;Choi J;Park J;Kong S;Park J;Goh J;Lee YH
分生孢子和附着胞的适当发育在包括稻瘟病菌（Magnaporthe oryzae）在内的许多真菌病原体的病害循环中至关重要。从稻瘟病菌基因组中鉴定出了总共8个编码假定的同源异型盒转录因子（TFs）的基因（MoHOX1到MoHOX8）。通过同源依赖的基因替换获得了每个MoHOX基因的敲除突变体。两个突变体ΔMohox3和ΔMohox5在生长、产孢、分生孢子大小、分生孢子萌发、附着胞形成和致病性方面与野生型没有差异。然而，与野生型相比，ΔMohox1的菌丝生长显著减少，黑色素沉着增加。ΔMohox4和ΔMohox6分别显示分生孢子大小和菌丝生长显著减少。ΔMohox8形成正常的附着胞，但没有致病性，可能是由于侵入钉发育和侵入性生长存在缺陷。最值得注意的是，ΔMohox2中的无性繁殖完全被废除，没有分生孢子形成。ΔMohox2仍然能够通过菌丝驱动的附着胞以类似于野生型的方式致病。然而，ΔMohox7既不能在分生孢子萌发管上也不能在菌丝顶端形成附着胞，不具有致病性。这些因素表明稻瘟病菌能够通过菌丝附着胞介导的穿透引起叶部病害，并且MoHOX7是驱动从菌丝和萌发管形成附着胞所必需的。转录分析表明稻瘟病菌同源异型盒转录因子的功能是通过基因表达的调控来介导的，并且受cAMP和Ca2 +信号传导和/或MAPK途径的影响。这组基因的不同作用可能有助于揭示稻瘟病菌及其近亲内基因组和调控途径是如何进化的。
病原体已经进化出多种致病策略。稻瘟病菌是引起稻瘟病的真菌植物病原体，被认为是理解真菌发育和致病性机制的重要模式生物。无性繁殖和与感染相关的发育在稻瘟病菌病害发展中起关键作用。稻瘟病菌的分生孢子分化出一种特殊结构——附着胞。附着胞产生膨压，使其能够通过机械破裂穿透寄主表皮层。在侵染寄主细胞后，真菌通过产孢产生大量分生孢子，作为多循环病害的二次繁殖体。为了阐明无性繁殖和附着胞介导的病害发展的分子机制，我们通过全基因组的计算机分析鉴定了8个同源异型盒转录因子。利用缺失突变体进行的特性分析表明，在稻瘟病菌发育过程中，每个同源异型盒转录因子都作为分生孢子形状、菌丝生长、产孢、附着胞发育和侵入性生长的阶段特异性调节剂发挥作用。值得注意的是，在ΔMohox2和ΔMohox7中，产孢和附着胞发育分别完全被废除。这项研究还提供了证据，表明稻瘟病菌能够在对寄主信号因子作出反应时通过菌丝驱动的附着胞引起稻瘟病。这项研究将有助于理解与真菌发育和致病性相关的调控网络。
The appropriate development of conidia and appressoria is critical in the disease cycle of many fungal pathogens, including Magnaporthe oryzae. A total of eight genes (MoHOX1 to MoHOX8) encoding putative homeobox transcription factors (TFs) were identified from the M. oryzae genome. Knockout mutants for each MoHOX gene were obtained via homology-dependent gene replacement. Two mutants, ΔMohox3 and ΔMohox5, exhibited no difference to wild-type in growth, conidiation, conidium size, conidial germination, appressorium formation, and pathogenicity. However, the ΔMohox1 showed a dramatic reduction in hyphal growth and increase in melanin pigmentation, compared to those in wild-type. ΔMohox4 and ΔMohox6 showed significantly reduced conidium size and hyphal growth, respectively. ΔMohox8 formed normal appressoria, but failed in pathogenicity, probably due to defects in the development of penetration peg and invasive growth. It is most notable that asexual reproduction was completely abolished in ΔMohox2, in which no conidia formed. ΔMohox2 was still pathogenic through hypha-driven appressoria in a manner similar to that of the wild-type. However, ΔMohox7 was unable to form appressoria either on conidial germ tubes, or at hyphal tips, being non-pathogenic. These factors indicate that M. oryzae is able to cause foliar disease via hyphal appressorium-mediated penetration, and MoHOX7 is mutually required to drive appressorium formation from hyphae and germ tubes. Transcriptional analyses suggest that the functioning of M. oryzae homeobox TFs is mediated through the regulation of gene expression and is affected by cAMP and Ca2+ signaling and/or MAPK pathways. The divergent roles of this gene set may help reveal how the genome and regulatory pathways evolved within the rice blast pathogen and close relatives. Pathogens have evolved diverse strategies to cause disease. Magnaporthe oryzae is the fungal phytopathogen that causes rice blast and is considered an important model for understanding mechanisms in fungal development and pathogenicity. Asexual reproduction and infection-related development play key roles in M. oryzae disease development. The conidium of M. oryzae differentiates a specialized structure, an appressorium. The appressorium generates turgor pressure that allows penetration through the mechanical rupture of host cuticle layers. After colonizing host cells, the fungus produces massive conidia via conidiogenesis, serving as secondary propagules for the polycyclic disease. To elucidate molecular mechanisms in asexual reproduction and appressorium-mediated disease development, we identified eight homeobox transcription factors through a genome-wide in silico analysis. Characterization using deletion mutants revealed that each homeobox TF functions as a stage-specific regulator for conidial shape, hyphal growth, conidiation, appressorium development, and invasive growth during M. oryzae development. Notably, conidiation and appressorium development were entirely abolished in ΔMohox2 and ΔMohox7, respectively. This study also provides evidence that M. oryzae is able to cause rice blast by means of hypha-driven appressoria upon responses to host signaling factors. This study will aid in the understanding of regulatory networks associated with fungal development and pathogenicity.
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