PubMed · 12610287
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J R McConnell, M K Barton. 2003-02-28. Botany. Leaf development takes shape.. https://doi.org/10.1126/science.1082433
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Forty populations from eight taxa belonging to six species of Antirrhinum were studied for electrophoretic differentiation at 14 allozyme loci. All the studied species show that marker alleles and genetic distances between conspecific populations are lower than for other species of the genus. Results permit the recognition of A. onubensis and A. boissieri at specific rank. The low level of genetic distance together with morphological characters and sympatric range, support the recognition of A. ambiguum as a new subspecies of A. graniticum, as A. graniticum ssp. ambiguum Mateu & Segarra stat. nov. The results of the study support separation of the studied taxa into two groups coinciding with subsections Streptosepalum and Antirrhinum, but disagreeing with the arrangement of species into them. According to the results of the study these groups consist of A. meonanthum and A. braun-blanquetii (Streptosepalum) and A. graniticum s.l., A. onubensis and A. boissieri (Antirrhinum). The status of A. meonanthum var. rothmaleri requires further clarification.
The CYCLOIDEA (CYC) and DICHOTOMA (DICH) genes encode related TCP transcription factors that control floral asymmetry in Antirrhinum majus. Analysis of sequences from relatives of Antirrhinum suggested that CYC and DICH arose from a gene duplication in an ancestor of the tribe Antirrhineae and have subsequently evolved at similar rates. Coding regions outside the conserved functional TCP and R domains differed by numerous indels, suggesting rapid evolution and low constraint on amino acid sequence. An analysis of variability within the genus Antirrhinum revealed very similar CYC alleles in 17 representative species, consistent with most of the species having diverged within the last 1 myr. Whereas substitution mutations appear to have accumulated constantly, one Antirrhinum CYC allele provided evidence for sporadic and rapid accumulation of insertion mutations.
CYCLOIDEA (CYC) and DICHOTOMA (DICH) are paralogous genes that determine adaxial (dorsal) flower identity in the bilaterally symmetric flowers of Antirrhinum majus (snapdragon). We show here that the duplication leading to the existence of both CYC and DICH in Antirrhinum occurred before the radiation of the Antirrhineae (the tribe to which snapdragon belongs). We find no additional gene duplications within Antirrhineae. Using explicit codon-based models of evolution in a likelihood framework, we show that patterns of molecular evolution after the duplication that gave rise to CYC and DICH are consistent with purifying selection acting at both loci, despite their known functional redundancy in snapdragon. However, for specific gene regions, purifying selection is significantly relaxed across DICH lineages, relative to CYC lineages. In addition, we find evidence for relaxed purifying selection along the lineage leading to snapdragon in one of two putative functional domains of DICH. A model of selection accounting for the persistence of paralogous genes in the absence of diversifying selection is presented. This model takes into account differences in the degree of purifying selection acting at the two loci and is consistent with subfunctionalization models of paralogous gene evolution.