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.
The nucleoside analogue 4-thiothymidine has shown great potential in vitro as a photosensitiser for the photodynamic therapy of numerous cancer cell lines. However, the limited penetrating power of UV-A radiation, to which it responds, raises doubts as to its practical usefulness in clinical applications. We addressed this issue by studying the penetration extent of topical thiothymidine and the antiproliferative effect of its combination with UV-A radiation on ex vivo basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) skin cancer biopsies, and normal skin. Our results show that both the intralesional concentration of the drug and the intensity of UV-A radiation are sufficient to activate the molecule and cause extensive death by apoptosis of the malignant cells. Normal skin biopsies were not significantly affected by the treatment.
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.
Gene and genome duplications play a major role in the evolution of plant species. The Brassica nigra genome is highly replicated as a result of ancient polyploidization events. Two copies of the flowering time gene CONSTANS (COa and COb) have been identified in B. nigra, and previous studies showed that COa is functional. In the present study, the polymorphism of 92 COb alleles sampled in seven populations was analyzed. Both polymorphism and recombination levels were elevated and varied strongly among populations and 8% of COb alleles exhibit apparently disabling mutations. Sequence data, however, do not provide unambiguous support for the presence of relaxed selective constraint on COb as compared to known functional CO genes. On the one hand, some of the disabling mutations reached high-frequency arguing for a loss of function but, on the other hand, the ratio of nonsynonymous to synonymous nucleotide polymorphism and diversity is low and similar to that observed in other B. nigra CO and CO-like genes, supporting the conservation of some function. We also showed that COb is still transcribed. Finally, the flowering time of Arabidopsis thaliana co mutant plants transformed with COb alleles with and without apparent disabling mutations was similar. We propose that COb was retained for a long period after duplication, but a recent fixation of a detrimental mutation, possibly as an effect of a bottleneck, resulted in its nonfunctionalization. We also speculate as to the presence of subsequent selection for rapid degeneration of the gene.
Previous QTL mapping identified a Brassica nigra homolog to Arabidopsis thaliana CO as a candidate gene affecting flowering time in B. nigra. Transformation of an A. thaliana co mutant with two different alleles of the B. nigra CO (Bni COa) homolog, one from an early-flowering B. nigra plant and one from a late one, did not show any differential effect of the two alleles on flowering time. The DNA sequence of the coding region of the two alleles was also identical, showing that nucleotide variation influencing flowering time must reside outside the coding region of Bni COa. In contrast, the nucleotide sequence of the B. nigra COL1 (Bni COL1) gene located 3.5 kb upstream of Bni COa was highly diverged between the alleles from early and late plants. One indel polymorphism in the Bni COL1 coding region, present in several natural populations of B. nigra, displayed a significant association with flowering time within a majority of these populations. These data indicate that a quantitative trait nucleotide (QTN) affecting flowering time is located within or close to the Bni COL1 gene. The intergenic sequence between Bni COL1 and Bni COa displayed a prominent peak of divergence 1 kb downstream of the Bni COL1 coding region. This region could contain regulatory elements for the downstream Bni COa gene. Our data suggest that a naturally occurring QTN for flowering time affects the function or expression of either Bni COL1 or Bni COa.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.