Genome-Wide Dissection of the CRF Gene Family in Brassica napus Indicates that BnaCRF8s Specifically Regulate Root Architecture and Phosphate Homeostasis against Phosphate Fluctuation in Plants

Phosphorus (P) is an essential macronutrient required for plant growth and development. The involvement of cytokinin response factors (CRFs) in phosphate (Pi) homeostasis and lateral root (LR) initiation in Arabidopsis has been revealed. However, little is known in oil crops. Here, we performed genome-wide dissection of the CRF family in Brassica napus to identify 44 members, which were evolutionally classified into 6 subgroups. Among them, four BnaCRF8 genes were strongly upregulated by P deprivation, and were selected to be further investigated. Time course qRT-PCR analyses showed that four BnaCRF8 genes were enhanced dramatically after 12 h of P stress. Analyses of the subcellular localization in tobacco leaves indicated that BnaA7.CRF8 and BnaC2.CRF8 were localized in the nucleus. The expression of BnaCRF8 genes had constant negative effects on primary root growth and LR initiation and growth, and it reduced Pi acquisition and plant growth in Arabidopsis. Moreover, the expression of Pi homeostasis-related genes was modulated in BnaA7.CRF8 overexpression plants. These results suggest that BnaCRF8 genes might negatively regulate root architecture and plant growth through transcriptional modification of Pi homeostasis-related components. Overall, this study suggests that upregulation of BnaCRF8 genes might be a smart adaptive strategy to cope with continuous Pi deficiency in the environment.