Isolation and Expression Profiling of a CONSTANS-Like Gene and Two FLOWERING LOCUS T-Like Genes from Spinacia oleracea L.

Erika Abe,Kaien Fujino,Yube Yamaguchi,Kiyoshi Masuda

doi:10.4236/ajps.2014.526420

Abstract

Spinach (Spinacia oleracea L.) develops leaf rosettes under short-day conditions, and starts reproductive growth including bolting and flowering under long-day conditions. Japanese people prefer Oriental spinach that bolts easily with a shorter photoperiod than European spinach. This is one of the main reasons that Oriental spinach is difficult to grow year-round. In order to understand spinach flowering mechanisms and obtain knowledge for spinach breeding, we isolated one CONSTANS-like (COL) and two FLOWERING LOCUS T (FT) homologs, which are key components of photoperiodic regulation of flowering time, from a Japanese cultivar. The expression of SoCOL1 showed diurnal rhythm with the highest expression at the end of the dark cycle. This diurnal rhythm is similar to the expression of BvCOL1 from sugar beet (Beta vulgaris), whose flower-promoting effect was observed when overexpressed in Arabidopsis. Phylogenetic analysis showed that SoCOL1 is the closest homolog of BvCOL1, suggesting that SoCOL1 is an ortholog of BvCOL1. SoFT1 and SoFT2 are closely related to BvFT1 and BvFT2, respectively. The expression of SoFT1 and SoFT2 were induced in advance of flower bud formation after changing the photoperiod, but the expression level of SoFT1 was much lower than SoFT2. Currently, we are speculating that SoFT2 is a flower-promoting factor of spinach, and that SoFT1 has a role in light signaling because the expression of SoFT1 showed a diurnal rhythm.

Highlights

Spinach (Spinacia oleracea L.) is a long-day plant, eaten at its vegetative growth stage, and one of the most popular vegetables in the world
Many studies have reported that FLOWERING LOCUS T (FT)-like genes and CONSTANS-like genes play crucial roles in flowering in various plant species [2]-[7]
As the first step in clarification of spinach flowering mechanisms, we isolated two FT homologs and one COL homolog, which were designated as SoFT1, SoFT2 and SoCOL1, respectively, through cDNA amplification of highly conserved regions by degenerate primers followed by 5’- and 3’-RACE

Summary

Introduction

Spinach (Spinacia oleracea L.) is a long-day plant, eaten at its vegetative growth stage, and one of the most popular vegetables in the world. After transition to the reproductive stage with flowering and bolting, spinach loses its value as an agricultural product, becoming bitter and hard. Oriental spinaches flower early, requiring only a 12- to 13-hour-photoperiod, and can be grown only from autumn to winter. European spinaches require a longer (14- to 16-hour-) photoperiod for flowering and have a bitter taste compared to Oriental spinaches, being more suitable for western-style foods such as sautés. Hybrid European and Oriental spinaches are used to provide spinach all year round in Japan, Oriental spinaches that require a longer photoperiod for flowering and bolting would be economically advantageous. In order to develop such spinach cultivars, it is necessary to understand flowering and bolting mechanisms of spinach at the genetic level

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