[Background & Methods]
Recently we have developed a method of gaining insight on plant-microbe interaction by using the methylotrophic yeast Candida boidinii and Arabidopsis thaliana as the model of microorganism and plant, respectively. We found that a considerable amount of methanol presented on the plant leaf surface and that its concentration changed during a plant daily light-dark cycle. In addition, methylotrophy and autophagy in C. boidinii are required for its survival and proliferation on living plant leaves (Kawaguchi et al., 2011). However, it is still unknown how this yeast response to the stresses at the phyllosphere.
In order to examine yeast stress response, various kinds of stress conditions such as osmotic stress, heat shock, and glucose deprivation were tested. In addition, we examined stress response of this yeast on the leaves of A. thaliana.
[Aims]
In the process of proliferation on the plant surface, C. boidinii is probably exposed to various environmental stresses. So we focused on cytoplasmic messenger ribonucleoprotein (mRNP) which plays key role on the quality control of mRNA especially under stress conditions. In this study, We tried to identify the core proteins of mRNPs (Edc3, Pat1, and Dcp2; processing body marker, Pab1, and Pbp1; stress granule marker) in C. boidinii and examine their intracellular localizations under various conditions including on the plant leaf surface.
[Results & Discussion]
In order to examine the dynamics of mRNP granules, the Edc3-Venus expressing strain and the Pbp1-Venus expressing strain were constructed. When these strains were observed under a variety of stress conditions including glucose deprivation and heat shock stress, the formation and increase of the number of mRNP granules were confirmed. Next, we constructed the edc3Δ, pat1Δ, and pbp1Δ strain and observed mRNP formation in these strains. We found that the formation of cytosolic pancta decreased drastically even under stress conditions. These results suggest that mRNP granules exist in the methylotrophic yeast C. boidinii as well as other eukaryotic cells and that visualization of these granules were possible. In order to examine the function of these granules on yeast survival at the phyllosphere, these Venus expressing strains were inoculated onto the upper side of plant leaves and observed by microscope. We found that the number of P-body increased remarkably whereas SG formation was not detected. These results indicate that P-body plays important roles on yeast proliferation at the phyllosphere.