The Response of COL and FT Homologues to Photoperiodic Regulation in Carrot (Daucus carota L.)

Lijie Liu,Xiangping Yan,Bo Liu,Zhiwei Zhao,Qi Shen,Min Li,Feiyun Zhuang,Xiaoping Kong,Chenggang Ou,Shumin Chen

doi:10.1038/s41598-020-66807-y

Abstract

Carrot (Daucus carota L.) is a biennial plant requiring vernalization to induce flowering, but long days can promote its premature bolting and flowering. The basic genetic network controlling the flowering time has been constructed for carrot, but there is limited information on the molecular mechanisms underlying the photoperiodic flowering response. The published carrot genome could provide an effective tool for systematically retrieving the key integrator genes of GIGANTEA (GI), CONSTANS-LIKE (COL), FLOWERING LOCUS T (FT), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) homologues in the photoperiod pathway. In this study, the bolting time of wild species “Songzi” (Ws) could be regulated by different photoperiods, but the orange cultivar “Amsterdam forcing” (Af) displayed no bolting phenomenon. According to the carrot genome and previous de novo transcriptome, 1 DcGI, 15 DcCOLs, 2 DcFTs, and 3 DcSOC1s were identified in the photoperiod pathway. The circadian rhythm peaks of DcGI, DcCOL2, DcCOL5a, and DcCOL13b could be delayed under long days (LDs). The peak value of DcCOL2 in Af (12.9) was significantly higher than that in Ws (6.8) under short day (SD) conditions, and was reduced under LD conditions (5.0). The peak values of DcCOL5a in Ws were constantly higher than those in Af under the photoperiod treatments. The expression levels of DcFT1 in Ws (463.0) were significantly upregulated under LD conditions compared with those in Af (1.4). These responses of DcCOL2, DcCOL5a, and DcFT1 might be related to the different bolting responses of Ws and Af. This study could provide valuable insights into understanding the key integrator genes in the carrot photoperiod pathway.

Highlights

The floral transition from a vegetative to a reproductive state is a critically important stage in the lifecycle of plants
During the late afternoons of long days (LDs), GI forms a complex with the FLAVIN-BINDING, KELCH REPEAT, F BOX 1 (FKF1) to degrade CYCLING DOF FACTORs (CDFs), which contains the major regulators of CO transcription, and CO protein accumulates to promote flowering by activating the transcription of FLOWERING LOCUST (FT) and TWIN SISTER OF FT (TSF) in the leaf vasculature[5,7,8,19,20,21]
Plants with 8–12 leaves are required to respond to a low temperature in carrot[41], but some landraces and cultivars can initiate bolting after a short vernalization period[52,53]

Summary

Introduction

The floral transition from a vegetative to a reproductive state is a critically important stage in the lifecycle of plants. Vernalization, photoperiod, ambient temperature, autonomous, gibberellin, and age pathways comprise a sophisticated regulatory network containing multiple endogenous and external factors that control flowering in Arabidopsis[1,2]. These pathways have their own unique initiations, but eventually converge to downstream key floral integrator genes, such as FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1)[1,2,3]. Through the effect of these integrator genes, the floral meristem-determining genes are activated to control the flowering time[8,11] This progress in the model plant Arabidopsis provides an important reference for researching floral molecular mechanisms in other crops[11,12]. This study provides an improved understanding of the regulatory network of photoperiodic flowering in carrots

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Conclusion