Abstract
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 (Malus×domestica) 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.
Highlights
Cytokinins (CTKs) play several essential roles in plant development, such as seed germination, leaf senescence, root and shoot branching, photosynthesis, flower, and fruit development, and act in response to environmental signaling [1,2,3,4]
As shown in these results, the identified apple cytokinin oxidases/dehydrogenases (CKXs) genes encoded proteins that ranged from 472 to 577 amino acids, with the protein mass ranging from 52.9 kD (MdCKX6.1) to 62.5 KD
The results revealed that these 10 MdCKX genes were mapped on 7 of 17 apple chromosomes, and 2 sister pairs of paralogous CKXs (MdCKX6.1/6.2, MdCKX7.1/7.2) were found on the duplicated blocks (Figure S1), proving that a scale segmental duplication event occurred in the apple genome
Summary
Cytokinins (CTKs) play several essential roles in plant development, such as seed germination, leaf senescence, root and shoot branching, photosynthesis, flower, and fruit development, and act in response to environmental signaling [1,2,3,4]. The enzyme isopentenyl transferase (IPT) catalyzes CTKs synthesis in plants [4]. The irreversible degradation of CTKs is catalyzed by cytokinin oxidases/dehydrogenases (CKXs), which are the only known enzymes that degrade CTKs and are encoded in plants by a small gene family [6]. The first CKX gene family has been identified in maize [10,11]. Several CKX genes have been identified and characterized in tobacco [12], Dendrobium orchid [13], Arabidopsis thaliana [14,15], Hordeum vulgare [7], Oryza sativa [16,17], Lotus japonicas [18], Vitis vinifera
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