Comparative Transcriptomic Analysis of Vernalization- and Cytokinin-Induced Floral Transition in Dendrobium nobile

Zhenzhen Wen,Jinchi Li,Wenzhong Guo,Wei Liu,Yunquan Liu,Qunyu Zhang,Chunmei He,Haisheng Lin

doi:10.1038/srep45748

Abstract

Vernalization is required for floral initiation in Dendrobium. Interestingly, those beneficial effects can also be achieved by exogenous cytokinin application in greenhouses. Thus, an as yet unknown crosstalk/interaction may exist between vernalization and cytokinin signaling pathways. In this study, we showed, by de novo transcriptome assembly using RNA-seq data from both vegetative and reproductive tissue samples, that some floral transition-related genes—DnVRN1, FT, SOC1, LFY and AP1—were differentially expressed in low-temperature-challenged (LT) or thidiazuron (TDZ)-treated plants, compared to those mock-treated (CK). Both LT and TDZ upregulated SOC1, LFY and AP1, while the upregulation of DnVRN1 and FT was only LT-induced. We further found that LT promoted the upregulation of some key cytokinin signaling regulators, including several cytokinin biosynthesis-related genes and type-B response regulator (RR)-encoding genes, and that both LT and TDZ triggered the significant upregulation of some marker genes in the gibberellin (GA) signaling pathway, indicating an important low temperature-cytokinin-GA axis in flowering. Our data thus have revealed a cytokinin-GA signal network underlying vernalization, providing a novel insight into further investigation of the molecular mechanism of floral initiation in Dendrobium.

Highlights

Vernalization is the process of promoting flowering in certain plants by prolonged exposure to the cold of winters
Two recent reports have demonstrated that endogenous cytokinin level is significantly increased in vernalization-induced reproductive development of Brassica napus plants[5], and that exogenous application of N6-benzylaminopurine (BAP), a synthetic cytokinin, promotes flowering in Arabidopsis grown in non-inductive short days through transcriptional activation of the FLOWERING LOCUS T (FT) paralogue TSF and SOC16
D. nobile is one of the most widespread ornamental members of orchid family, but the control of flowering time still remains a bottleneck in production

Summary

Introduction

Vernalization is the process of promoting flowering in certain plants by prolonged exposure to the cold of winters. Two recent reports have demonstrated that endogenous cytokinin level is significantly increased in vernalization-induced reproductive development of Brassica napus plants[5], and that exogenous application of N6-benzylaminopurine (BAP), a synthetic cytokinin, promotes flowering in Arabidopsis grown in non-inductive short days through transcriptional activation of the FT paralogue TSF and SOC16. Dendrobium is one of the largest genera of the Orchidaceae and consists of more than 1200 species[8], most of which are important commercial orchids that account for 20% of total orchid sales. They fall into two categories, nobile-type and phalaenopsis-type, which in horticulture are usually sold as potted and cut flowers, respectively[9]. Cytokinin treatment was demonstrated to stimulate flowering as early as 1978 in a sympodial orchid hybrid Dendrobium Louisae[12], but the underlying molecular mechanisms remain largely unknown

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