Verticillium dahliae, a soil-borne ascomycete fungus, causes destructive vascular wilt disease in hundreds of dicotyledonous plants, including many economically important crops and fruits, such as cotton, tobacco, sunflower, tomato, potato, eggplant and lettuce. Recently, a Chinese research group depict the whole epidermal invasion and vascular proliferation process using the state-of-the-art technologies; live-cell imaging and high-resolution scanning electron microscopy (SEM). These important findings shed light on the effective control of Verticillium wilts for the future of agriculture.
Danger is everywhere when plants grow, crafty pathogenic fungi are ready to find ways to attack the plant and absorb its nutrition at all times, so as to achieve endless reproduction. Verticillium dahliae, a typical one of them, is a soil-borne, filamentous fungal pathogen that causes destructive Verticillium wilt, a plant disease in over 400 plant species, and results in destructive crop losses annually. It is extremely difficult to control Verticillium wilt mainly because V. dahliae is a vasculature-colonizing pathogen and there are no efficient treatments. Thus, the comprehensive understanding of V. dahliae pathogenesis needs to be addressed, aiming to control Verticillium wilt effectively.
In a recent article, a Chinese research group unveiled the mystery of the infection strategy of V. dahliae. They elaborated the epidermal invasion and vascular proliferation/colonization strategy of V. dahliae in host plants by live-cell imaging combined with high-resolution scanning electron microscopy (SEM). Firstly, they used green fluorescent protein (GFP) labelled V. dahliae (V592-GFP) and observed the infection process of V. dahliae in host plants by “spinning-disc” confocal microscopy. The observations demonstrated that the apex (tip) of invading hyphae of V. dahliae become tapered and directly invade into the intercellular space of root epidermal cells at the initial infection (16-24 hours post inoculation) (see Movie 1). It does not form any conspicuous infection structure like appressoria, only slight hyphal swellings are formed before epidermal invasion. Following successful epidermal invasion, the invading hyphae extend in the intercellular space of the root cortex toward the vascular tissues. After reaching the vascular tissue, invasive hyphae differentiate into simple conidiophores to produce a huge number of conidia for further invasive proliferation (see Figure 1). The conidia are produced at the tip of the hyphae in a continuous budding-like process (see Movie 2). Moreover, the smart hyphae seem to like to make the most of every pore, freely crossing adjacent xylem vessels through the inter-tracheary pits to achieve horizontal colonization (see Figure 1).
These findings are significant for us to see how V. dahliae infects host plants and to believe we can cure the infected plants by taking targeted measures.
Movie 1: The process of invasive hyphae of V. dahliae invade into the junctions of root epidermal cells by 4D construction.
V. dahliae expressing cytoplasmic GFP (green, V592-GFP) and A. thaliana expressing PIP2A-mCherry (magenta). The yellow arrows indicate the invasion sites.
Movie 2 The conidial production of the V592 in the liquid medium. Scale bar represents 10 μm.
Juan Tian and Zhaosheng Kong published this study in Molecular Plant Pathology:
TITLE IMAGE: Still from a movie of Verticillium dahliae expressing cytoplasmic GFP (green, V592-GFP) infecting A. thaliana expressing PIP2A-mCherry (magenta). The yellow arrows indicate the invasion sites. All images used with permission of the author.
