Figure 1.

Model of IQD scaffolding function. (A) IQD proteins localize to the PM, MTs and cell nucleus, where they recruit CaM2 (and possibly other CaM/CML isoforms) as well as KLCR1/CMU1. Individual IQDs differentially affect MT organization and cell shape, which points to roles of plant-specific IQD families as a multifaceted toolbox for the regulation of cellular growth. ARF-mediated transcriptional control of IQD gene expression possibly links auxin and Ca²⁺ signaling. (B) IQD proteins share hallmarks of scaffold proteins, and interact with apo-CaM and Ca²⁺-CaM in vitro. We hypothesize that IQD proteins sequester apo-CaM and related Ca²⁺ sensors at distinct subcellular sites of Ca²⁺ influx to organize and integrate CaM/CML-dependent Ca²⁺ signaling.