Comparative transcriptome analysis of flower bud transition and functional characterization of EjAGL17 involved in regulating floral initiation in loquat.

Yan Xia,Shuming Wang,Di Wu,Danlong Jing,Baogui Xue,Guolu Liang,Qiao He,Min Shi,Qigao Guo,Feng Zhan,Maoteng Li

doi:10.1371/journal.pone.0239382

Abstract

Floral initiation plays a critical role for reproductive success in plants, especially fruit trees. However, little information is known on the mechanism of the initiation in loquat (Eriobotrya japonica Lindl.). Here, we used transcriptomic, expression and functional analysis to investigate the candidate genes in floral initiation in loquat. Comparative transcriptome analysis showed differentially expressed genes (DEGs) were mainly enriched in the metabolic pathways of plant hormone signal transduction. The DEGs were mainly involved in the gibberellin, auxin, cytokinin, abscisic acid, salicylic acid and ethylene signaling pathways. Meanwhile, some transcription factors, including MADS-box (MCM1, AGAMOUS, DEFICIENS and SRF), MYB (Myeloblastosis), TCP (TEOSINTE BRANCHED 1, CYCLOIDEA and PCF1), WOX (WUSCHEL-related homeobox) and WRKY (WRKY DNA-binding protein), were significantly differentially expressed. Among these key DEGs, we confirmed that an AGL17 ortholog EjAGL17 was significantly upregulated at the flower bud transition stage. Phylogenetic tree analysis revealed that EjAGL17 was grouped into an AGL17 clade of MADS-box transcription factors. Protein sequence alignment showed that EjAGL17 included a distinctive C-terminal domain. Subcellular localization of EjAGL17 was found only in the nucleus. Expression levels of EjAGL17 reached the highest at the development stage of flower bud transition. Moreover, ectopic expression of EjAGL17 in Arabidopsis significantly exhibited early flowering. Our study provides abundant resources of candidate genes for studying the mechanisms underlying the floral initiation in loquat and other Rosaceae species.

Highlights

Floral initiation is a critical phase for reproductive success in the life cycle of plants [1, 2]
The paraffin section observation of the apical buds showed that the transformation from vegetative to reproductive growth was from vegetative apex (VA) to flower bud transition (FBT) (Fig 1Vc and 1Fc)
The differentially expressed genes (DEGs) were mainly involved in the hormone signal transduction pathways and transcription factor genes

Summary

Introduction

Floral initiation is a critical phase for reproductive success in the life cycle of plants [1, 2]. Molecular mechanisms of floral initiation are based primarily on studies in the model plant Arabidopsis [2,3,4]. Transcriptomics is an effective method for discovering the gene networks and regulatory mechanisms underlying floral initiation in non-model plants [14,15,16]. In Rosa chinensis, comparative transcriptome analysis of the floral transition revealed that differentially expressed genes (DEGs) are mainly involved in the pathways of vernalization, photoperiod and gibberellin (GA) [14]. In Agropyron cristatum, transcriptomic analysis of floral transition indicated that DEGs are mainly involved in plant circadian clock pathway and flowering timeassociated genes [15]. Comparative transcriptome analysis indicated that DEGs of cytokinin biosynthesis pathway are mainly associated with floral transition in Dendrobium nobile. Global gene expression changes of floral initiation in Eriobotrya remain unknown and need further investigated

Methods

Results

Discussion

Conclusion