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.