Clade III HIPP genes encode plasmodesmata-targeted proteins with pleiotropic functions in regulating plant development.

Heavy metal-associated isoprenylated plant proteins (HIPPs) are encoded by large gene families, which have diversified specifically in vascular plants. Their physiological functions and molecular mode of activity are currently largely unknown. In this study, we characterize a group of phylogenetically closely related genes HIPP32, HIPP33, and HIPP34 in Arabidopsis thaliana, revealing their essential roles in controlling diverse developmental pathways. Through comprehensive genetic analyses, we demonstrate that these genes exhibit partially overlapping pleiotropic functions, influencing multiple aspects of plant growth such as embryogenesis, maintenance of apical meristems, root architecture, shoot branching, leaf morphogenesis and floral organ formation. Transcriptomic profiling of hipp mutants identified significant deregulation in several regulatory pathways involved in plant hormone responses, with a specific impact on auxin signaling processes. Interestingly, we show that the analyzed HIPP proteins localize very specifically to plasmodesmata, suggesting their potential function in regulating intercellular communication in shaping plant development.