Low red/far-red ratio can induce cytokinin degradation resulting in the inhibition of tillering in wheat (Triticum aestivum L.)

Kangqi Lei; Qingwen Tan; Liqi Zhu; Libing Xu; Shuke Yang; Jinling Hu; Lijun Gao; Pan Hou; Yuhang Shao; Dong Jiang; Weixing Cao; Tingbo Dai; Zhongwei Tian

doi:10.3389/fpls.2022.971003

Low red/far-red ratio can induce cytokinin degradation resulting in the inhibition of tillering in wheat (Triticum aestivum L.)

Front Plant Sci. 2022 Dec 8:13:971003. doi: 10.3389/fpls.2022.971003. eCollection 2022.

Authors

Kangqi Lei¹, Qingwen Tan¹, Liqi Zhu¹, Libing Xu¹, Shuke Yang¹, Jinling Hu¹, Lijun Gao¹, Pan Hou¹, Yuhang Shao², Dong Jiang¹, Weixing Cao¹, Tingbo Dai¹, Zhongwei Tian¹

Affiliations

¹ Key Laboratory of Crop Physiology Ecology and Production Management of Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China.
² National Agricultural Exhibition Center (China Agricultural Museum), Chaoyang District, Beijing, China.

Abstract

Shoot branching is inhibited by a low red/far-red ratio (R/FR). Prior studies have shown that the R/FR suppressed Arabidopsis thaliana branching by promotes bud abscisic acid (ABA) accumulation directly. Given that wheat tiller buds are wrapped in leaf sheaths and may not respond rapidly to a R/FR, systemic cytokinin (CTK) may be more critical. Here, systemic hormonal signals including indole-3-acetic acid (IAA), gibberellins (GA) and CTK and bud ABA signals in wheat were tested under a low R/FR. The results showed that a low R/FR reduced the percentage of tiller occurrence of tiller IV and the tiller number per plant. The low R/FR did not rapidly induced ABA accumulation in the tiller IV because of the protection of the leaf sheath and had little effect on IAA content and signaling in the tiller nodes. The significant change in the CTK levels was observed earlier than those of other hormone (ABA, IAA and GA) and exogenous cytokinin restored the CTK levels and tiller number per plant under low R/FR conditions. Further analysis revealed that the decrease in cytokinin levels was mainly associated with upregulation of cytokinin degradation genes (TaCKX5, TaCKX11) in tiller nodes. In addition, exposure to a decreased R/FR upregulated the expression of GA biosynthesis genes (TaGA20ox1, TaGA3ox2), resulting in elevated GA levels, which might further promote CTK degradation in tiller nodes and inhibit tillering. Therefore, our results provide evidence that the enhancement of cytokinin degradation is a novel mechanism underlying the wheat tillering response to a low R/FR.

Keywords: cytokinin; degradation; hormone; low R/FR; tillering; wheat.