Department of Plant-Microbe Interactions, Max-Planck Institute for Plant Breeding Research, D-50829 Cologne, Germany.
Plant Physiol. 2010 Mar;152(3):1544-61. doi: 10.1104/pp.109.147660. Epub 2009 Dec 18.
Arabidopsis (Arabidopsis thaliana) genes MILDEW RESISTANCE LOCUS O2 (MLO2), MLO6, and MLO12 exhibit unequal genetic redundancy with respect to the modulation of defense responses against powdery mildew fungi and the control of developmental phenotypes such as premature leaf decay. We show that early chlorosis and necrosis of rosette leaves in mlo2 mlo6 mlo12 mutants reflects an authentic but untimely leaf senescence program. Comparative transcriptional profiling revealed that transcripts of several genes encoding tryptophan biosynthetic and metabolic enzymes hyperaccumulate during vegetative development in the mlo2 mlo6 mlo12 mutant. Elevated expression levels of these genes correlate with altered steady-state levels of several indolic metabolites, including the phytoalexin camalexin and indolic glucosinolates, during development in the mlo2 single mutant and the mlo2 mlo6 mlo12 triple mutant. Results of genetic epistasis analysis suggest a decisive role for indolic metabolites in mlo2-conditioned antifungal defense against both biotrophic powdery mildews and a camalexin-sensitive strain of the necrotrophic fungus Botrytis cinerea. The wound- and pathogen-responsive callose synthase POWDERY MILDEW RESISTANCE4/GLUCAN SYNTHASE-LIKE5 was found to be responsible for the spontaneous callose deposits in mlo2 mutant plants but dispensable for mlo2-conditioned penetration resistance. Our data strengthen the notion that powdery mildew resistance of mlo2 genotypes is based on the same defense execution machinery as innate antifungal immune responses that restrict the invasion of nonadapted fungal pathogens.
拟南芥（Arabidopsis thaliana）基因 MILDEW RESISTANCE LOCUS O2（MLO2）、MLO6 和 MLO12 在调节对白粉病真菌的防御反应以及控制发育表型（如过早的叶片衰老）方面表现出不等的遗传冗余性。我们表明，mlo2 mlo6 mlo12 突变体中，初生叶的早期黄化和坏死反映了一种真实但过早的叶片衰老程序。比较转录谱分析显示，编码色氨酸生物合成和代谢酶的几个基因的转录物在 mlo2 mlo6 mlo12 突变体的营养生长发育过程中大量积累。这些基因的表达水平升高与几种吲哚代谢物的稳态水平改变相关，包括植物抗毒素 camalexin 和吲哚葡萄糖苷，在 mlo2 单突变体和 mlo2 mlo6 mlo12 三突变体的发育过程中。遗传上位性分析的结果表明，吲哚代谢物在 mlo2 条件下对生物亲和性白粉病和坏死性真菌 Botrytis cinerea 的 camalexin 敏感菌株的抗真菌防御中起着决定性作用。发现创伤和病原体响应性的几丁质合酶 POWDERY MILDEW RESISTANCE4/GLUCAN SYNTHASE-LIKE5 负责 mlo2 突变体植物中自发的几丁质沉积，但对 mlo2 条件下的穿透抗性是可有可无的。我们的数据加强了这样的观点，即 mlo2 基因型的白粉病抗性基于与限制非适应性真菌病原体入侵的先天抗真菌免疫反应相同的防御执行机制。
