Transcriptional Regulations on the Low-Temperature-Induced Floral Transition in anOrchidaceaeSpecies,Dendrobium nobile: An Expressed Sequence Tags Analysis

Shan Liang,Qing-Sheng Ye,Mei-Ru Li,Jia-Yi Leng,Xiao-Jing Wang,Hong-Qing Li,Rui-Hong Li

doi:10.1155/2012/757801

Abstract

Vernalization-induced flowering is a cold-relevant adaptation in many species, but little is known about the genetic basis behind in Orchidaceae species. Here, we reported a collection of 15017 expressed sequence tags (ESTs) from the vernalized axillary buds of an Orchidaceae species, Dendrobium nobile, which were assembled for 9616 unique gene clusters. Functional enrichment analysis showed that genes in relation to the responses to stresses, especially in the form of low temperatures, and those involving in protein biosynthesis and chromatin assembly were significantly overrepresented during 40 days of vernalization. Additionally, a total of 59 putative flowering-relevant genes were recognized, including those homologous to known key players in vernalization pathways in temperate cereals or Arabidopsis, such as cereal VRN1, FT/VRN3, and Arabidopsis AGL19. Results from this study suggest that the networks regulating vernalization-induced floral transition are conserved, but just in a part, in D. nobile, temperate cereals, and Arabidopsis.

Highlights

Transition from the vegetative phase to the flowering phase is crucial to both development and reproduction in plants
The “flower development” subcategory was not overrepresented as expected, which led to a speculation that transition to the flowering stage would not occur, but we found that the frequency of this subcategory increased gradually with time during the vernalization process, and many homologs involved in various pathways promoting the floral transition and flowering development were induced after the low-temperature treatment
VRN2 homologs were not found in rice [8], nor could we find in the D. nobile expressed sequence tags (ESTs) collection, which suggested that this gene, as well as the VRN2-containing PRC2 complex, may be absent in this Orchidaceae species

Summary

Introduction

Transition from the vegetative phase to the flowering phase is crucial to both development and reproduction in plants. The expression of FLC is suppressed by vernalization through enrichment of H3K27m3 on the chromatin [3], which releases FT and SOC1 from inhibition by FLC to promote the transition to flowering. This FLC-dependant pathway is regulated by both temperature and day length [4]. AGL19, a close relative of SOC1, is believed to mediate an FLC-independent pathway that activates flowering under vernalization in Arabidopsis [1] This process is associated with a cold-induced decrease of H3K27m3 on AGL19 locus and probably with the loss of function of CLF and MSI1 or the involved complex [5]. FLC is thought to be central to the control of flowering in Arabidopsis and probably in most other dicots [1, 2]

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Conclusion