Root Infection and Systematic Colonization of DsRed-Labeled Fusarium verticillioides in Maize

Fusarium verticillioides (Sacc.) Nirenberg [syn. F. moniliforme J. Sheld., teleomorph: Gibberella fujikuroi (Sawada) Ito in Ito & K. Kimura] is an important causal agent of diseases in maize (Zea mays L.) worldwide, which invades maize plants at all growth stages. This filamentous fungus not only incites obvious symptoms on maize root, stem, and ear, but also is able to infect plants without any visible symptom (endophytic infection). Fluorescent reporter gene-labeled filamentous fungus permits in vitro and in planta monitoring growth and development of the fungus. In this study, gene DsRed encoding red fluorescent protein was delivered into F. verticillioides strain Fv-1 via Agrobacterium tumefaciens-mediated transformation. Using the DsRed-tagged F. verticillioides, systemic colonization of the fungus in root and stem of the susceptible maize inbred line B73 was investigated to understand the interaction between F. verticillioides and maize. The fungus invaded and multiplied inside the lateral root tissues. Some conidia tended to colonize on the veins of maize root surface and grow along the veins after their germination. Whereas, some others penetrated the plant cells where they attached and formed hyphae for attacking cells nearby. Usually, the mycelia migrated from root to stem through intercellular parts of tissues, while some mycelia ran across different host cells. The colony forming unit (CFU) values from root tended to decrease following the inoculation time, but those from stem inclined to increase. This indicates that F. verticillioides is able to attack the aboveground parts of plant via systemic colonization on root. The results from the present study are useful in disclosing the interaction between F. verticillioides and maize, and can be extended to studying interactions between other soil-borne fungi and plants.

摘要采用农杆菌介导法将红色荧光蛋白基因DsRed转入轮枝镰孢Fv-1菌株, 利用荧光显微镜观察轮枝镰孢在玉米自交系B73根部定殖和生长的规律。土壤中的轮枝镰孢首先侵染玉米的须根等组织, 并在其中大量增殖, 随后沿主根向上侵染, 以菌丝的形式扩展到地上组织。有些孢子附着在根表面的纹理中, 萌发形成菌丝而扩展; 有的则向内侵染附着的细胞, 然后再继续向周边侵染。由根内部向上侵染的菌丝多沿着细胞间隙上行, 有些也会穿行在不同细胞之间。分析接种不同时间轮枝镰孢在玉米根和茎基部组织形成的单菌落数量(CFU)发现, 轮枝镰孢在根部的CFU值随时间逐渐减小, 而茎基部的CFU值则呈逐渐增大的趋势。这说明土壤中的轮枝镰孢能够通过根系侵染途径危害地上部组织。本研究的结果为进一步探明轮枝镰孢和玉米之间的互作关系, 以及其他土传真菌与植物之间的互作提供了有益的参考。