Identification of Flowering-Related Genes Responsible for Differences in Bolting Time between Two Radish Inbred Lines

Abstract

Late bolting after cold exposure is an economically important characteristic of radish (Raphanus sativus L.), an important Brassicaceae root vegetable crop. However, little information is available regarding the genes and pathways that govern flowering time in this species. We performed high-throughput RNA sequencing analysis to elucidate the molecular mechanisms that determine the differences in flowering times between two radish lines, NH-JS1 (late bolting) and NH-JS2 (early bolting). In total, 71,188 unigenes were identified by reference-guided assembly, of which 309, 788, and 980 genes were differentially expressed between the two inbred lines after 0, 15, and 35 days of vernalization, respectively. Among these genes, 218 homologs of Arabidopsis flowering-time (Ft) genes were identified in the radish, and 49 of these genes were differentially expressed between the two radish lines in the presence or absence of vernalization treatment. Most of the Ft genes up-regulated in NH-JS1 vs. NH-JS2 were repressors of flowering, such as RsFLC, consistent with the late-bolting phenotype of NH-JS1. Although, the functions of genes down-regulated in NH-JS1 were less consistent with late-bolting characteristics than the up-regulated Ft genes, several Ft enhancer genes, including RsSOC1, a key floral integrator, showed an appropriate expression to the late-bolting phenotype. In addition, the patterns of gene expression related to the vernalization pathway closely corresponded with the different bolting times of the two inbred lines. These results suggest that the vernalization pathway is conserved between radish and Arabidopsis.

Genome-wide identification, characterization, and evolutionary analysis of flowering genes in radish (Raphanus sativus L.)

“…In our study, 38 R. sativus genes were identified as floral integrators or were associated with the flower meristem, including SOC1 , FT , AP1 , LFY , and FD . Jung et al (2016) did not detect R. sativus LFY through transcriptomic analysis [ 45 ], while, we detect two copies, although they both little expressed , which indicated LFY may expressed in specific periods and tissues.…”

“…Three R. sativus FLC homologs were identified in this study, which is consistent with the findings of a transcript-level analysis by Yi et al (2014), and their functions in transgenic A. thaliana have been examined [ 52 ]. Jung et al (2016) also did not detect R. sativus FRI homologue through RNA-seq, while we identified two copies and both expressed [ 45 ]. The existence and expression of FLC and FRI in R. sativus indicate that the FLC/FRI mode of action on vernalization is conserved, as are the components of the autonomous pathway [ 53 ].…”

The oilseed rape developmental expression resource: a resource for the investigation of gene expression dynamics during the floral transition in oilseed rape

“…In particular, three radish FLC orthologues (RsFLC1, RsFLC2, and RsFLC3) have been identified, all of which repress flowering when overexpressed in Arabidopsis [32]. Expression of the RsFLC1 gene was also found to be higher in a late-bolting radish variety relative to an early-bolting variety, consistent with the role FLC plays in Arabidopsis and Brassica species [33].…”

Translating Flowering Time from Arabidopsis thaliana to Brassicaceae and Asteraceae Crop Species

“…Three copies of RsFLC were detected and all three act as flowering repressors when overexpressed in A. thaliana [103]. RsFLC expression before vernalization was enhanced in a late- compared to an early-bolting R. sativus inbred line, and reduced during vernalization or after GA treatment [18,104,105]. Overall, negative regulators of the vernalization pathway, such as RsFLC, RsMAF2, RsSPA1 , and RsAGL18 , were highly expressed in the late-bolting line, whereas positive regulators of vernalization, such as RsVRN1 , RsVIN3 , and RsAGL19 were relatively highly expressed in the early-bolting line [104].…”

“…Before vernalization, expression level of one RsGA2ox homolog was upregulated in a late compared to early bolting line. Expression level of one homolog of RsGID1a was induced by vernalization treatment [104].…”