Transcriptome profiling of litchi leaves in response to low temperature reveals candidate regulatory genes and key metabolic events during floral induction

Hongna Zhang,Yongzan Wei,Houbin Chen,Jiyuan Shen

doi:10.1186/s12864-017-3747-x

Abstract

BackgroundLitchi (Litchi chinensis Sonn.) is an economically important evergreen fruit tree widely cultivated in subtropical areas. Low temperature is absolutely required for floral induction of litchi, but its molecular mechanism is not fully understood. Leaves of litchi played a key role during floral induction and could be the site of low temperature perception. Therefore, leaves were treated under different temperature (15 °C/25 °C), and high-throughput RNA sequencing (RNA-Seq) performed with leaf samples for the de novo assembly and digital gene expression (DGE) profiling analyses to investigate low temperature-induced gene expression changes.Results83,107 RNA-Seq unigenes were de novo assembled with a mean length of 1221 bp and approximately 61% of these unigenes (50,345) were annotated against public protein databases. Differentially-expressed genes (DEGs) under low temperature treatment in comparison with the control group were the main focus of our study. Hierarchical clustering analysis arranged 2755 DEGs into eight groups with three significant expression clusters (p-value ≤ 0.05) during floral induction. With the increasing contents of sugars and starch, the expression of genes involved in metabolism of sugars increased dramatically after low temperature induction. One FT gene (Unigene0025396, LcFT1) which produces a protein called ‘florigen’ was also detected among DEGs of litchi. LcFT1 exhibited an apparent specific tissue and its expression was highly increased after low temperature induction, GUS staining results also showed GUS activity driven by LcFT1 gene promoter can be induced by low temperature, which indicated LcFT1 probably played a pivotal role in the floral induction of litchi under low temperature.ConclusionsOur study provides a global survey of transcriptomes to better understand the molecular mechanisms underlying changes of leaves in response to low temperature induction in litchi. The analyses of transcriptome profiles and physiological indicators will help us study the complicated metabolism of floral induction in the subtropic evergreen plants.

Highlights

Litchi (Litchi chinensis Sonn.) is an economically important evergreen fruit tree widely cultivated in subtropical areas
This study provides a global survey of transcriptomes from litchi leaves exposed to low temperature of different time through de novo assembly of generation sequencing technique
This study provides a platform for understanding the molecular mechanisms underlying changes in response to low temperature treatment in leaves, and will benefit researches in flowering mechanisms of evergreen fruit trees

Summary

Introduction

Litchi (Litchi chinensis Sonn.) is an economically important evergreen fruit tree widely cultivated in subtropical areas. Previous studies have shown that low temperature is a crucial environmental cue for floral induction of subtropical evergreen plants, litchi [2,3,4,5,6], olive [7], mango [8, 9], citrus [10,11,12] and orchid [13], all of which require a certain period of relatively low temperature to induce flowering. There are still plenty of unresolved questions about litchi flowering, knowledge of the molecular events associated with the low temperature signals that activate flowering of evergreen plants remains obscure, and the events occurring in leaves of litchi during floral induction should be worth exploring

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