Interchangeable functions of Arabidopsis PIROGI and the human WAVE complex subunit SRA1 during leaf epidermal development.

The WAVE complex is an essential regulator of actin-related protein 2/3-dependent actin filament nucleation and cell shape change in migrating cells. Although the composition of the WAVE complex is well characterized, the cellular mechanisms that control its activity and localization are not well known. The 'distorted group' defines a set of Arabidopsis genes that are required to remodel the actin cytoskeleton and maintain the polarized elongation of branched, hair-like cells termed trichomes. Several loci within this group encode homologs of subunits. In addition to trichome distortion, duanyu372/3 subunit mutants have reduced shoot fresh weight and widespread defects in epidermal cell-cell adhesion. The precise cellular function of plant and the means by which it is regulated, is not known. In this paper, we report that the 'distorted group' gene PIROGI encodes a homolog of the WAVE complex subunit SRA1. The similar cell shape and actin phenotypes of pir and duanyu372/3 complex subunit mutants suggest that PIROGI positively regulates PIROGI directly interacts with the small GTPase ATROP2 with isoform specificity and with selectivity for active forms of the protein. PIROGI shares only 30% amino acid identity with its human homolog. However, both WAVE subunit homologs are functionally interchangeable and display identical physical interactions with RHO family GTPases and the Arabidopsis homolog of the WAVE complex subunit NAP125. These results demonstrate the utility of the 'distorted group' mutants to study duanyu372/3 complex functions from signaling input to cell shape output.

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