Characterizing the Role of the Alpha/Beta Hydrolase Comparative Gene Identification-58 in Arabidopsis thaliana

Comparative Gene Identification-58 (CGI-58), an alpha/beta hydrolase protein, is responsible for maintaining triacylglycerol (TAG) levels in lipid-storing mammalian cells. The disruption of this gene in humans, as seen in patients diagnosed with Chanarin-Dorfman syndrome, is known to cause an abnormal accumulation of TAG in non-lipid storing tissues. Interestingly, the disruption of the CGI-58 homologue in Arabidopsis thaliana has a similar effect, resulting in a significant increase in TAG levels within the leaves and stems of the plant. To gain insight to the function of CGI-58 in A. thaliana, we examined the phenotype of plants disrupted in CGI-58 activity through the use of germination and establishment assays, and identified proteins that directly interact with CGI-58 by utilizing the yeast two-hybrid screening system. Our findings were as follows: (i) the CGI-58 protein interacts with PXA1, a peroxisomal transporter known to be important for seed germination, metabolism of lipid hormones (e.g., auxins), and breakdown of storage oils during post-germinative growth; (ii) Plants disrupted in CGI-58 activity displayed aberrant response to auxin hormones in cell elongation assays; and (iii) CGI-58 is not required for seed germination or oil breakdown during seedling establishment under optimal conditions, but is required for proper seed germination in the presence of elevated amounts of abscisic acid (ABA), a stress-related hormone. In summary, CGI-58 appears to play a vital role in a variety of lipid signaling pathways in plants including auxin metabolism, which is essential for proper plant growth and development, and ABA sensitivity, which is important for aiding seeds and plants during response to various environmental stresses.