Genome-Wide Identification and Expression Profiling of Cytokinin Oxidase/Dehydrogenase (CKX) Genes Reveal Likely Roles in Pod Development and Stress Responses in Oilseed Rape (Brassica napus L.)

Abstract

Cytokinin oxidase/dehydrogenases (CKXs) play a critical role in the irreversible degradation of cytokinins, thereby regulating plant growth and development. <i>Brassica napus</i> is one of the most widely cultivated oilseed crops worldwide. With the completion of whole-genome sequencing of <i>B. napus</i>, genome-wide identification and expression analysis of the <i>BnCKX</i> gene family has become technically feasible. In this study, we identified 23 <i>BnCKX</i> genes and analyzed their phylogenetic relationships, gene structures, conserved motifs, protein subcellular localizations, and other properties. We also analyzed the expression of the 23 <i>BnCKX</i> genes in the <i>B. napus</i> cultivar Zhong Shuang 11 ('ZS11') by quantitative reverse-transcription polymerase chain reaction (qRT-PCR), revealing their diverse expression patterns. We selected four <i>BnCKX</i> 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 <i>BnCKX5-1</i>, <i>5-2</i>, <i>6-1</i>, and <i>7-1</i> 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 <i>BnCKX</i> genes. Our results suggest that regulating <i>BnCKX</i> expression is a promising way to enhance the harvest index and stress resistance in plants.