School of Biosciences, University of Exeter, Exeter EX4 4QD, United Kingdom.
Plant Cell. 2010 Feb;22(2):497-507. doi: 10.1105/tpc.109.072447. Epub 2010 Feb 26.
To gain entry to plants, many pathogenic fungi develop specialized infection structures called appressoria. Here, we demonstrate that appressorium morphogenesis in the rice blast fungus Magnaporthe oryzae is tightly regulated by the cell cycle. Shortly after a fungus spore lands on the rice (Oryza sativa) leaf surface, a single round of mitosis always occurs in the germ tube. We found that initiation of infection structure development is regulated by a DNA replication-dependent checkpoint. Genetic intervention in DNA synthesis, by conditional mutation of the Never-in-Mitosis 1 gene, prevented germ tubes from developing nascent infection structures. Cellular differentiation of appressoria, however, required entry into mitosis because nimA temperature-sensitive mutants, blocked at mitotic entry, were unable to develop functional appressoria. Arresting the cell cycle after mitotic entry, by conditional inactivation of the Blocked-in-Mitosis 1 gene or expression of stabilized cyclinB-encoding alleles, did not impair appressorium differentiation, but instead prevented these cells from invading plant tissue. When considered together, these data suggest that appressorium-mediated plant infection is coordinated by three distinct cell cycle checkpoints that are necessary for establishment of plant disease.
为了进入植物体内，许多病原真菌会形成专门的感染结构，称为附着胞。在这里，我们证明了稻瘟病菌（Magnaporthe oryzae）附着胞形态发生受到细胞周期的严格调控。在真菌孢子落在水稻（Oryza sativa）叶片表面后不久，在芽管中总是会发生一轮有丝分裂。我们发现，感染结构发育的起始受到一个依赖于 DNA 复制的检查点的调控。通过条件性突变 Never-in-Mitosis 1 基因对 DNA 合成进行遗传干预，阻止了芽管发育新生的感染结构。然而，附着胞的细胞分化需要进入有丝分裂，因为在有丝分裂进入时被阻断的 nimA 温度敏感突变体无法发育出功能性的附着胞。在有丝分裂进入后通过条件性失活 Blocked-in-Mitosis 1 基因或表达稳定的细胞周期蛋白 B 编码等位基因来阻断细胞周期，不会损害附着胞的分化，但会阻止这些细胞侵入植物组织。综合这些数据表明，附着胞介导的植物感染受到三个不同的细胞周期检查点的协调，这些检查点对于建立植物病害是必要的。
