Abstract
Cytokinin oxidase/dehydrogenases (CKXs) play a critical role in the irreversible degradation of cytokinins, thereby regulating plant growth and development. Brassica napus is one of the most widely cultivated oilseed crops worldwide. With the completion of whole-genome sequencing of B. napus, genome-wide identification and expression analysis of the BnCKX gene family has become technically feasible. In this study, we identified 23 BnCKX genes and analyzed their phylogenetic relationships, gene structures, conserved motifs, protein subcellular localizations, and other properties. We also analyzed the expression of the 23 BnCKX genes in the B. napus cultivar Zhong Shuang 11 (‘ZS11’) by quantitative reverse-transcription polymerase chain reaction (qRT-PCR), revealing their diverse expression patterns. We selected four BnCKX genes based on the results of RNA-sequencing and qRT-PCR and compared their expression in cultivated varieties with extremely long versus short siliques. The expression levels of BnCKX5-1, 5-2, 6-1, and 7-1 significantly differed between the two lines and changed during pod development, suggesting they might play roles in determining silique length and in pod development. Finally, we investigated the effects of treatment with the synthetic cytokinin 6-benzylaminopurine (6-BA) and the auxin indole-3-acetic acid (IAA) on the expression of the four selected BnCKX genes. Our results suggest that regulating BnCKX expression is a promising way to enhance the harvest index and stress resistance in plants.
Highlights
Cytokinins promote cell division, regulate root and shoot differentiation synergistically with auxin [1,2,3,4,5], release apical dominance, and delay leaf senescence [6,7,8]
Using A. thaliana AtCKX protein sequences as queries, seven AtCKXs, 23 BnCKXs, 12 BoCKXs and 12 BrCKXs were identified via BLASTP analysis
Genome-wide analysis and expression profiling of the cytokinin oxidase/dehydrogenases (CKXs) gene family have been performed in Arabidopsis and the diploid B. rapa, revealing 7 and 12 CKX
Summary
Cytokinins promote cell division, regulate root and shoot differentiation synergistically with auxin [1,2,3,4,5], release apical dominance, and delay leaf senescence [6,7,8]. Cytokinin biosynthetic and metabolic enzymes play critical roles in maintaining cytokinin concentrations in individual cells or tissues at the proper level for normal functioning [11]. CKXs act on specific substrates such as isopentenyladenine and isopentenyladenine riboside [15]. These enzymes catalyze the irreversible degradation of cytokinins and their derivatives by removing their N6 -substituted isoprene chains [16]. In this catalytic reaction, CKX enzymes display a dual catalytic mode in conjunction with molecular oxygen or other specific substances, which act as electron acceptors [17]. CKXs can function as flavin enzymes by covalently binding to flavin adenine dinucleotide (FAD) via a histidine residue, and they contain both
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