Corral-Ramos Cristina, Roca M Gabriela, Di Pietro Antonio, Roncero M Isabel G, Ruiz-Roldán Carmen
a Departamento de Genética; Universidad de Córdoba; Campus de Excelencia Agroalimentario ; Córdoba , Spain.
Autophagy. 2015;11(1):131-44. doi: 10.4161/15548627.2014.994413.
In the fungal pathogen Fusarium oxysporum, vegetative hyphal fusion triggers nuclear mitotic division in the invading hypha followed by migration of a nucleus into the receptor hypha and degradation of the resident nucleus. Here we examined the role of autophagy in fusion-induced nuclear degradation. A search of the F. oxysporum genome database for autophagy pathway components identified putative orthologs of 16 core autophagy-related (ATG) genes in yeast, including the ubiquitin-like protein Atg8, which is required for the formation of autophagosomal membranes. F. oxysporum Foatg8Δ mutants were generated in a strain harboring H1-cherry fluorescent protein (ChFP)-labeled nuclei to facilitate analysis of nuclear dynamics. The Foatg8Δ mutants did not show MDC-positive staining in contrast to the wild type and the FoATG8-complemented (cFoATG8) strain, suggesting that FoAtg8 is required for autophagy in F. oxysporum. The Foatg8Δ strains displayed reduced rates of hyphal growth, conidiation, and fusion, and were significantly attenuated in virulence on tomato plants and in the nonvertebrate animal host Galleria mellonella. In contrast to wild-type hyphae, which are almost exclusively composed of uninucleated hyphal compartments, the hyphae of the Foatg8Δ mutants contained a significant fraction of hyphal compartments with 2 or more nuclei. The increase in the number of nuclei per hyphal compartment was particularly evident after hyphal fusion events. Time-lapse microscopy analyses revealed abnormal mitotic patterns during vegetative growth in the Foatg8Δ mutants. Our results suggest that autophagy mediates nuclear degradation after hyphal fusion and has a general function in the control of nuclear distribution in F. oxysporum.
在真菌病原体尖孢镰刀菌中，营养菌丝融合会触发入侵菌丝中的核有丝分裂，随后一个细胞核迁移到受体菌丝中，并使驻留的细胞核降解。在此，我们研究了自噬在融合诱导的核降解中的作用。通过在尖孢镰刀菌基因组数据库中搜索自噬途径成分，鉴定出了酵母中16个核心自噬相关（ATG）基因的假定直系同源物，包括泛素样蛋白Atg8，它是自噬体膜形成所必需的。在一个带有H1-樱桃荧光蛋白（ChFP）标记细胞核的菌株中构建了尖孢镰刀菌Foatg8Δ突变体，以利于分析核动态。与野生型和FoATG8互补（cFoATG8）菌株相比，Foatg8Δ突变体未显示出MDC阳性染色，这表明FoAtg8是尖孢镰刀菌自噬所必需的。Foatg8Δ菌株的菌丝生长、产孢和融合速率降低，并且在番茄植株和非脊椎动物宿主大蜡螟上的毒力显著减弱。与几乎完全由单核菌丝隔室组成的野生型菌丝不同，Foatg8Δ突变体的菌丝含有相当一部分具有两个或更多细胞核的菌丝隔室。在菌丝融合事件后，每个菌丝隔室中细胞核数量的增加尤为明显。延时显微镜分析揭示了Foatg8Δ突变体营养生长期间异常的有丝分裂模式。我们的结果表明，自噬介导菌丝融合后的核降解，并在尖孢镰刀菌核分布的控制中具有普遍作用。
