Before fungi begin to infect a host, they first undergo a dramatic physical change and grow filaments that look like twigs on a leafless tree. The hormone indole-3-acetic acid (IAA) regulates how plants grow, causing them to extend shoots towards sunlight. Previous work by Prusty Rao and others has shown that yeast take-up IAA from the environment to stimulate the growth of filaments. In the current study, Prusty Rao's team found that yeast also produce IAA themselves and secrete it into the environment around them. In this manner, the ongoing secretion and uptake of IAA presumably becomes a feedback loop giving the yeast information about the number of yeast nearby. If there are many yeast secreting IAA, then there is more in the environment to take up.
Furthermore, Prusty Rao's team found that when the concentration of IAA reached a certain threshold, the fungus began to change shape and grow filaments (see figure), providing "strong support" for a connection between the yeasts' production of IAA and fungal infection.
"If there is just one yeast cell sitting under your toe nail, then it won't be a problembut if there are a thousand yeast cells there, then they can begin to filament and cause infection," Prusty Rao noted. "We believe the data show that IAA plays a role in the yeast's ability to know when there are sufficient numbers of them in close enough proximity to try and infect a host, be it a plant or a person."
|Contact: Michael Cohen|
Worcester Polytechnic Institute