Plant & zo
The science of plants and more
Pathogens are shrewd operators while entering a plant and stealing its nutrients. They use proteins that manipulate the plant, preventing it from noticing the intruders. Most of them work hard to repress the plant’s immune response. So that it cannot raise the alarm. But this turned out not to be true for the manipulative protein Six5 of the fungus Fusarium oxysporum.
Fusarium oxysporum is the cause of vascular wilt disease. The fungus is entering the plant through its roots, and finally nestles itself in the transport system of the plant. To get there, the fungus manipulative proteins are essential. Mostly these manipulators work alone, but Avr2 and Six5 are forming a pair. Dutch and British researchers studied what mischief they were up to.
Of Avr2 it is known that it is suppressing the plant’s immune system. To find out if Six5 is doing this as well, the researchers created plants that make six5 themselves. Subsequently the researchers analysed how these plants deal with infections. In contrast to plants that make themselves Avr2, plants that make Six5 mostly do not react differently to infections than plants without Six5. Except when Avr2 is brought in through the pathogen, then, so noticed the researchers, the infection starts of quicker. Six5 by itself is not suppressing the immune system. But what is doing?
Six5 helps other fungal manipulators to spread faster
To efficiently suppress the immune system of the plant it is useful for the fungal manipulators to move quickly from cell to cell. Plant cells have for their own communication small connections between cells, plasmodesmata. Through these throughfares molecules and small proteins can travel. For the manipulators the ideal way to spread.
The researchers studied if Six5 and Avr2 could influence the size of these throughfares. For this they infected leaves with Six5, Avr2 and fluorescent proteins. Only when the throughfare of the plasmodesmata are big enough can the fluorescent proteins travel to neighbouring cells. The researchers noticed that without Six5 and Avr2 the fluorescent proteins did not travel outside their cell, but with Six5 and Avr2 present they did. Six5 and Avr2 increased the throughfare between the cells. Making it easier for manipulative fungal proteins to travel from cell to cell.
Manipulator Six5 is playing a crucial role during the Fusarium oxysporum infection. It helps other fungal manipulators to spread faster. So, the fungus can nestle itself inside the plants transport system before the plants immune system notices that there is an unwelcome visitor.
Blekemolen MC, Cao L, Tintor N, de Groot T, Papp D, Faulkner C and Takken FLW (2022) The primary function of Six5 of Fusarium oxysporum is to facilitate Avr2 activity by together manipulating the size exclusion limit of plasmodesmata. Front. Plant Sci. 13:910594. doi: 10.3389/fpls.2022.910594