Genome-wide identification of IQ67 domain (IQD) gene families in Chinese jujube (Ziziphus jujuba Mill.) and expression profiles in response to cold stress

The plant-specific IQ67 DOMAIN (IQD) gene family is a possible targeted interacting protein of calmodulin that plays important roles in calcium signaling transduction and that functions in various biotic and abiotic stresses. However, no systematic analysis of the IQD gene family has been performed in Chinese jujube (Ziziphus jujuba Mill.). In the current study, 20 ZjIQDs were first identified in Chinese jujube and found to be evenly distributed on 12 chromosomes (chr) except chr 9 through a series of bioinformatic analyses. Phylogenetic analysis of 20 ZjIQDs with the IQDs in rice and Arabidopsis showed that all of the IQDs could be classified into four groups and that each group could be divided into two or three other subgroups. In addition, gene structure and motif composition analysis showed that 20 ZjIQDs had similar/respective gene structures in the same group and that the IQ calmodulin binding motif was conserved. Prediction of calmodulin binding sites revealed that all of the ZjIQDs contained at least one calmodulin binding site, which might indicate that they could be targeted by calmodulin. Syntenic analysis indicated that eight ZjIQDs showed syntenic relationships with those in Arabidopsis and four ZjIQDs showed syntenic relationships with those in rice. The expression profiles of ZjIQDs in response to cold, salt and alkaline stresses showed that most ZjIQDs were up- or downregulated, but ZjIQD15 and 16 were significantly upregulated under these stresses. In addition, ZjIQD15 was significantly regulated by oryzalin treatment (a microtubule disruption drug). Moreover, several ZjIQDs were differentially expressed between diploid and autotetraploid 'Dongzao' in response to cold stress, which might have important functions in the regulation of the differential cold resistance between diploid and autotetraploid 'Dongzao'. This systematic analysis of ZjIQDs could provide important information for further functional characterization of key ZjIQDs in response to cold stress with the aim of breeding cold-resistant cultivars, especially improving the cold tolerance of autotetraploid 'Dongzao'.