The IQD Family of Calmodulin-Binding Proteins Links Calcium Signaling to Microtubules, Membrane Subdomains, and the Nucleus

Abstract

ORCID IDs: 0000-0002-3493-4800 (K.B.); 0000-0002-7146-043X (B.M.).Calcium (Ca 2+ ) signaling and dynamic reorganization of the cytoskeleton are essential processes for the coordination and control of plant cell shape and cell growth. Calmodulin (CaM) and closely related calmodulin-like (CML) polypeptides are principal sensors of Ca 2+ signals. CaM/CMLs decode and relay information encrypted by the second messenger via differential interactions with a wide spectrum of targets to modulate their diverse biochemical activities. The plant-specific IQ67 DOMAIN (IQD) family emerged as possibly the largest class of CaM-interacting proteins with undefined molecular functions and biological roles. Here, we show that the 33 members of the IQD family in Arabidopsis (Arabidopsis thaliana) differentially localize, using green fluorescent protein (GFP)-tagged proteins, to multiple and distinct subcellular sites, including microtubule (MT) arrays, plasma membrane subdomains, and nuclear compartments. Intriguingly, the various IQD-specific localization patterns coincide with the subcellular patterns of IQD-dependent recruitment of CaM, suggesting that the diverse IQD members sequester Ca 2+ -CaM signaling modules to specific subcellular sites for precise regulation of Ca 2+ -dependent processes. Because MT localization is a hallmark of most IQD family members, we quantitatively analyzed GFP-labeled MT arrays in Nicotiana benthamiana cells transiently expressing GFP-IQD fusions and observed IQD-specific MT patterns, which point to a role of IQDs in MT organization and dynamics. Indeed, stable overexpression of select IQD proteins in Arabidopsis altered cellular MT orientation, cell shape, and organ morphology. Because IQDs share biochemical properties with scaffold proteins, we propose that IQD families provide an assortment of platform proteins for integrating CaM-dependent Ca 2+ signaling at multiple cellular sites to regulate cell function, shape, and growth.

Rice microtubule‐associated protein IQ67‐DOMAIN14 regulates grain shape by modulating microtubule cytoskeleton dynamics

“…Moreover, hypocotyls of the dark‐grown p35S::OsIQD14:GFP seedlings were highly sensitive to Oryzalin (Figure e‐f), further supporting the role of OsIQD14 in controlling MT stability (Komaki et al , ; Nakamura et al , ). Further analysis of whether OsIQD14 overexpression could change the cell shape of Arabidopsis hypocotyl cells showed the much elongated hypocotyl cells of Arabidopsis lines expressing OsIQD14 (p35S::OsIQD14:GFP) compared to those of TUA6 marker line (p35S::GFP:TUA6, Figure S4c‐e), similar to AtIQD16 (Burstenbinder et al , ), and confirming the OsIQD14 effects on cell shape.…”

“…IQD proteins contain a conserved, 67 amino acid domain and were first identified in Arabidopsis where it is represented by a 33‐member gene family (Abel et al , ). Evidence form Arabidopsis showed that IQDs play important roles in leaf shape determination and xylem secondary cell wall architecture (Burstenbinder et al , ; Liang et al , ; Sugiyama et al , ). Most of the IQD genes have distinct expression patterns, preferentially in embryo, stomata, meristematic cells and elongating tissues (Burstenbinder et al , ; Wendrich et al , ).…”

Transient alkalinization of the leaf apoplast stiffens the cell wall during onset of chloride salinity in corn leaves

“…Betatubulins are basic cytoplasmic proteins that form together with alpha-tubulins the microtubules which are a major component of the cytoskeleton (26). The dynamic microtubule cytoskeleton network coordinates cellular transport, cell shape, cell division and cell growth (27,28). In dependency to the alkalinization, we observe an increased abundance of a number of tubulins (Table 3).…”

PaCeQuant: A Tool for High-Throughput Quantification of Pavement Cell Shape Characteristics

“…IQD16 belongs to a novel class of calmodulinbinding proteins with potential roles in cellular calcium signaling (Abel et al, 2005;Abel et al, 2013). Most IQD family members localize to microtubules, and overexpression of IQD16 alters microtubule organization and induces cell elongation (Bürstenbinder et al, 2017a;Bürstenbinder et al, 2017b). As input, we used 10 images per genotype of cotyledons from 5-d-old seedlings (Fig.…”

“…Seeds of the ktn1-5 T-DNA line (SAIL_343_D12) were obtained from the Nottingham Arabidopsis Stock Centre (NASC). Transgenic Pro-35S:IQD16 lines were generated by Agrobacterium tumefaciens-mediated transformation using the floral-dip method (Clough and Bent, 1998), as described in Bürstenbinder et al (2017b). Arabidopsis seeds were surface-sterilized with chlorine gas, and after 2 d of stratification at 4°C grown vertically on square plates containing Arabidopsis salt (ATS) medium and 0.5% (w/v) agar (Lincoln et al, 1990) at 20°C with cycles of 16 h light and 8 h dark.…”