Interaction Of HSP90 and miRNAs Through Argonaute Proteins In The Buffering of Phenotypic Variation In Arabidopsis thaliana

Robustness to genetic and environmental perturbations is a fundamental property of biological systems. Previous work has demonstrated the importance of the molecular chaperone HSP90 in maintaining organismal robustness. HSP90 inhibition reveals cryptic genetic and epigenetic variation with significant phenotypic consequences in flies, fish, plants, and yeast. The molecular mechanisms underlying the release of HSP90-dependent variation are not well understood. Recent studies found that microRNAs (miRNAs) are also important in maintaining robustness due to their function in modulating gene expression. In humans and flies, HSP90 is required for the formation of the miRNA-silencing complex. Moreover, in tobacco cell lines, HSP90 interacts physically with ARGONAUTE1 (AGO1), a key protein in the plant miRNA pathway, and a component of the miRNA-silencing complex. We hypothesize that HSP90 and miRNAs interact in maintaining organismal robustness in A. thaliana.

Using established assays for HSP90 function, we demonstrate that HSP90 and AGO1 interact genetically in the buffering of phenotypic variation in early seedlings. AGO1 polymorphisms correlate with sensitivity to HSP90 inhibition of divergent A. thaliana strains. Currently, we are exploring to what extent HSP90- and AGO1-dependent variation overlap. We compare AGO1’s buffering potential and breadth to HSP90 by crossing ago1 and hsp90 mutants into different A. thaliana accessions.

The A. thaliana Argonaute family is comprised of 10 members. Among these, we show that AGO10 and AGO5, the closests AGO1 paralogs, do not interact with HSP90. We are investigating whether other Argonautes interact genetically with HSP90 to understand HSP90’s role on the diversification of this important gene family.