Efforts to develop more environmentally friendly alternatives to traditional broad-spectrum pesticides in agriculture have recently turned to RNA interference (RNAi) technology. With the built-in, sequence-specific knockdown of gene targets following delivery of double-stranded RNA (dsRNA), RNAi offers the promise of controlling pests and pathogens without adversely affecting non-target species. Significant advances in the efficacy of this technology have been observed in a wide range of species, including many insect pests and fungal pathogens. Two different dsRNA application methods are being developed. First, host induced gene silencing (HIGS) harnesses dsRNA production through the thoughtful and precise engineering of transgenic plants and second, spray induced gene silencing (SIGS) that uses surface applications of a topically applied dsRNA molecule. Regardless of the dsRNA delivery method, one aspect that is critical to the success of RNAi is the ability of the target organism to internalize the dsRNA and take advantage of the host RNAi cellular machinery. The efficiency of dsRNA uptake mechanisms varies across species, and in some uptake is negligible, rendering them effectively resistant to this new generation of control technologies. If RNAi-based methods of control are to be used widely, it is critically important to understand the mechanisms underpinning dsRNA uptake. Understanding dsRNA uptake mechanisms will also provide insight into the design and formulation of dsRNAs for improved delivery and provide clues into the development of potential host resistance to these technologies.

In response to Ca2+ signals, the evolutionarily‐conserved Ca2+ sensor calmodulin (CaM) regulates protein targets via direct interaction. Plants possess many CaM‐like (CML) proteins, but their binding partners and functions are mostly unknown. Here, using Arabidopsis CML13 as ‘bait’ in a yeast two‐hybrid screen, we isolated putative targets from three, unrelated protein families, namely, IQD proteins, calmodulin‐binding transcriptional activators (CAMTAs) and myosins, all of which possess tandem isoleucine‐glutamine (IQ) structural domains. Using the split‐luciferase complementation assay in planta and the yeast 2‐hybrid system, CML13 and CML14 showed a preference for interaction with tandem over single IQ domains. Relative to CaM, CML13 and CML14 displayed weaker signals when tested with the non‐IQ, CaM‐binding domain of glutamate decarboxylase or the single IQ domains of CNGC20 (cyclic‐nucleotide gated channel‐20) or IQM1 (IQ motif protein1). We examined IQD14 as a representative tandem IQ‐protein and found that only CaM, CML13 and CML14 interacted with IQD14 among 12 CaM/CMLs tested. CaM, CML13 and CML14 bound in vitro to IQD14 in the presence or absence of Ca2+. Binding affinities were in the nM range and were higher when two tandem IQ domains from IQD14 were present. Green fluorescent protein‐tagged versions of CaM, CML13 and CML14 localized to both the cytosol and nucleus in plant cells but were partially relocalized to the microtubules when co‐expressed with IQD14 tagged with mCherry. These and other data are discussed in the context of possible roles for these CMLs in gene regulation via CAMTAs and cytoskeletal activity via myosins and IQD proteins.