Multiple flowering time QTLs within severalBrassicaspecies could be the result of duplicated copies of one ancestral gene

Abstract

Quantitative trait locus (QTL) analysis was used to study the evolution of genes controlling the timing of flowering in four Brassica genomes that are all extensively replicated. Comparative mapping showed that a chromosomal region from the top of Arabidopsis thaliana chromosome 5 corresponded to three homoeologous copies in each of the diploid species Brassica nigra, B. oleracea, and B. rapa and six copies in the amphidiploid B. juncea. QTLs were detected in two of the three replicated segments in each diploid genome and in three of the six replicated segments in B. juncea. These results indicate that, for the studied trait, multiple QTLs resulting from genome duplication is the rule rather than the exception. Brassica homologues to two candidate genes (CO and FLC) identified from the corresponding A. thaliana region were mapped. CO homologues mapped close to the QTL peaks in eight of nine QTLs, while FLC homologues mapped farther away in those cases where the mapping resolution allowed a comparison. Thus, our data are consistent with the hypothesis that all the major QTLs we detected in the different species of Brassica could be the result of duplicated copies of the same ancestral gene, possibly the ancestor of CO.

Development of Microsatellite Markers in Melon (Cucumis melo L.) and Their Application to Major Cucurbit Crops.

“…It is interesting to determine whether loci controlling these common traits are derived from homologous parts of the genome. Quantitative trait loci controlling the flowering time of several Brassica species were reported in homologous parts of the genomes (Axelsson et al 2002). Since a large number of the present primer sets enabled to identify microsatellite loci in these cucurbit crops, homology studies using these microsatellite loci may provide information on the loci controlling these common traits, and clarify the relationships among the genomes of these species.…”

Mapping of QTLs for Bolting Time in Brassica rapa (syn. campestris) under Different Environmental Conditions

“…Integration of SSR markers into the present linkage map could be useful for MAS for bolting time in breeding programs of Brassica plants. Furthermore, since Brassica species are closely related to the model plant Arabidopsis, in which the flowering-time pathways have been extensively studied, the flowering-time genes from Arabidopsis could be used as RFLP probes for mapping the loci in Brassica species (Teutonico and Osborn 1994, Kole et al 2001, Axelsson et al 2001. Because many of the genes related to flowering time have been identified and classified into a few functional pathways, including the photoperiod and vernalization promotion pathways in Arabidopsis (Koornneef et al 1998, Simpson et al 1999, the understanding of how the effects of QTL alleles were altered by environmental factors will provide clues for the identification of the candidate genes responsible for bolting time in B. rapa.…”

“…Therefore, although bolting time was evaluated in the present study, flowering time was more frequently used for QTLmapping because of the simplicity of the measurement. QTLmapping for flowering time in B. rapa was reported in several populations (Teutonico and Osborn 1995, Osborn et al 1997, Axelsson et al 2001. These studies showed that QTL-mapping is a useful method for analyzing such traits.…”

“…Diploid Brassica species are considered to be derived from a common hexaploid ancestor (Lagercrantz andLydiate 1996, Lagercrantz 1998). Axelsson et al (2001) showed that the top region of the Arabidopsis chromosome V harboring several genes that control flowering time is conserved as three homologous copies in each of the diploid species B. rapa, B. oleracea and B. nigra and six copies in the amphidiploid species B. juncea. Indeed, Tadege et al (2001) isolated five FLOWERING LOCUS C (FLC)-related sequences from B. napus, and Schranz et al (2002) cloned four B. rapa FLC homologues.…”

Simple Sequence Repeat-Based Comparative Genomics Between Brassica rapa and Arabidopsis thaliana: The Genetic Origin of Clubroot Resistance

“…Genomic synteny has been found to be well conserved among a broad array of species, even though genomic size in plant exhibits a wide diversity, e.g., 125 Mb for A. thaliana to 125 Gb for Fritillaria assyriaca (Bennett and Smith 1976). Physically and functionally conserved gene(s), known as orthologs and paralogs, were also identified (Axelsson et al 2001). Because Brassica and Arabidopsis are in the same family, the Cruciferae, the level of synteny between them provides a good opportunity to study how genetic and morphological variation has developed during the evolution of the genome, including the endurance of certain genetic structures in Arabidopsis and related Brassica species.…”