Abstract:

The plant-specific IQ67-domain (IQD) gene family, a key factor encoding calmodulin-binding proteins and calcium signaling scaffold proteins, constitutes the core hub of the calcium signaling regulatory network in plants. Members of this family exhibit distinct structural characteristics: the N-terminal conserved IQ67 domain specifically recruits calmodulin, while the C-terminal DUF4005 domain anchors microtubules. In horticultural crops, the core functions of the IQD family are mostly focused on fruit morphogenesis — it modulates the orientation of microtubule arrays to determine the cell division plane, thereby directly regulating fruit shape. Meanwhile, as a multidimensional signal integration node, the IQD family deeply mediates the crosstalk between calcium signaling and phytohormone pathways (including auxin, gibberellin, cytokinin,and abscisic acid), as well as stress responses to biotic and abiotic stresses such as pathogen infection, salt and drought stress. Although the molecular interactions and cellular regulatory networks of IQD genes in Arabidopsis thaliana have been systematically elucidated, there remain notable gaps in the depth and systematicness of mechanistic characterization in horticultural crop research. Even though multiple key IQD genes have been identified in major horticultural crops such as Solanum lycopersicum and Cucumis sativus, most studies are still limited to gene-phenotype correlation analysis, with relatively inadequate characterization of microtubule dynamics at the cellular level and the mechanisms of multi-signal integration. Based on a systematic review of the research progress of IQD genes in major horticultural crops, this paper focuses on synthesizing their core molecular mechanisms in fruit shape regulation, cytoskeleton remodeling and signal cascades, standardizes gene nomenclature, and comprehensively clarifies the current research limitations. Future research should focus on the molecular functional characterization of IQD proteins as calcium signaling scaffolds, aiming to provide a theoretical reference for improving the regulatory networks governing the growth and development of horticultural crops and facilitating the molecular design breeding of high-quality and stress-tolerant cultivars.

Key words: IQD gene family, fruit morphology, microtubule cytoskeleton, horticultural crops, calcium signal, hormone signal, stress response