Identification and Functional Characterization of Apple MdCKX5.2 in Root Development and Abiotic Stress Tolerance

Cytokinin oxidase/dehydrogenases (CKXs) are the key enzymes in cytokinin degradation and have been widely studied in model plants. Little is known about apple's (Malusxdomestica) CKX genes. Here, using genome-wide analysis, we identified 10 MdCKX genes in apple. The phylogenetics, chromosome locations, and genome structures were then tested. Expression analysis showed that MdCKX genes had different expression profiles in apple, pointing to the different roles. Meanwhile, relative expression analysis showed that these genes have different expression patterns in response to several exogenous cytokinin factors, including trans-zeatin (ZT), thidiazuron (TDZ), and N6-furfuryladenine (KT). Finally, we introduced the MdCKX5.2 gene into Arabidopsis to evaluate its functions, and the results suggested the transgenic Arabidopsis displayed phenotypes related to promoting primary root and lateral root development, response to exogenous ZT, and conferring to drought and salt tolerant. Taken together, our results provide insights on the possible application of the MdCKX5.2 gene for molecular breeding in apples.

Automated summary

This study identified 10 MdCKX genes in apple through genome-wide analysis and further investigated their phylogenetics, chromosome locations, and genome structures. Expression analysis revealed different expression profiles and roles of these genes in apple. Transgenic Arabidopsis experiments showed that the MdCKX5.2 gene plays a significant role in promoting root development, responding to exogenous cytokinins, and conferring drought and salt tolerance in apples.