Abstract
Onion bulbing is an important agricultural trait affecting economic value and is regulated by flowering-related genes. FLOWERING LOCUS T (FT)-like gene function is crucial for the initiation of flowering in various plant species and also in asexual reproduction in tuber plants. By employing various computational analysis using RNA-Seq data, we identified eight FT-like genes (AcFT) encoding PEBP (phosphatidylethanolamine-binding protein) domains in Allium cepa. Sequence and phylogenetic analyses of FT-like proteins revealed six proteins that were identical to previously reported AcFT1-6 proteins, as well as one (AcFT7) with a highly conserved region shared with AcFT6 and another (comp106231) with low similarity to MFT protein, but containing a PEBP domain. Homology modelling of AcFT7 proteins showed similar structures and conservation of amino acids crucial for function in AtFT (Arabidopsis) and Hd3a (rice), with variation in the C-terminal region. Further, we analyzed AcFT expression patterns in different transitional stages, as well as under SD (short-day), LD (long-day), and drought treatment in two contrasting genotypic lines EM (early maturation, 36101) and LM (late maturation, 36122). The FT transcript levels were greatly affected by various environmental factors such as photoperiod, temperature and drought. Our results suggest that AcFT7 is a member of the FT-like genes in Allium cepa and may be involved in regulation of onion bulbing, similar to other FT genes. In addition, AcFT4 and AcFT7 could be involved in establishing the difference in timing of bulb maturity between the two contrasting onion lines.
Highlights
Angiosperms, a diverse group of flowering plants, have evolved to carry out complex developmental processes, from vegetative to reproductive growth, that are greatly affected by endogenous and environmental factors [1,2]
As onion has a limited number of transcript sequences available so far, we performed an in-silico search to identify FLOWERING LOCUS T (FT) genes from the RNA-Seq data of transcripts assembled from the leaf tissues of the two Korean onion lines 36101 and 36122 (SRP064878)
To extend our search for new FT genes, we used a gene prediction tool (HMMER) to identify candidate FT genes based on their protein domain (PEBP domain) structure
Summary
Angiosperms, a diverse group of flowering plants, have evolved to carry out complex developmental processes, from vegetative to reproductive growth, that are greatly affected by endogenous and environmental factors [1,2]. The flowering cycle is regulated by various factors and pathways including photoperiod, vernalization, gibberellins, ambient temperature, age and autonomous pathways [3,4]. Flowering occurs following a period of vernalization [5] and is influenced by three major genes, VRN1, VRN2, and FLOWERING LOCUS T (FT, known as VRN3) [6]. The FT gene was first identified in Arabidopsis thaliana [7,8], in which it plays a major role in the vernalization and photoperiod pathway and in initiating the flowering signal in the apical meristem. Previous study in model plant Arabidopsis revealed translocation of FT proteins, a component of florigen [9], to the apical meristem from leaf tissues. FT proteins induce flowering after long distance transport, acting as an mobile flowering signal [10]. CONSTANS (CO) acts as Molecules 2016, 21, 217; doi:10.3390/molecules21020217 www.mdpi.com/journal/molecules
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