Comparative physical mapping of segments of the genome of Brassica oleracea var. alboglabra that are homoeologous to sequenced regions of chromosomes4 and 5 of Arabidopsis thaliana
Cm. O'Neill et I. Bancroft, Comparative physical mapping of segments of the genome of Brassica oleracea var. alboglabra that are homoeologous to sequenced regions of chromosomes4 and 5 of Arabidopsis thaliana, PLANT J, 23(2), 2000, pp. 233-243
Due to their relatedness to Arabidopsis thaliana (Arabidopsis), the cultiva
ted Brassica species represent the first group of crops with which to evalu
ate comparative genomics approaches to understanding biological processes a
nd manipulating traits. We have constructed a high-quality binary BAC libra
ry (JBo) from genomic DNA of Brassica oleracea var. alboglabra, in order to
underpin such investigations. Using the Arabidopsis genome sequence and cl
ones from the JBo library, we have analysed aspects of gene conservation an
d microsynteny between a 222 kb region of the genome of Arabidopsis and hom
oeologous segments of the genome of B. oleracea. All 19 predicted genes tes
ted were found to hybridize to clones in the JBo library, indicating a high
level of gene conservation. Further analyses and physical mapping with the
BAC clones identified allowed us to construct clone contig maps and analys
e in detail the gene content and organization in the set of paralogous segm
ents identified in the genome of B. oleracea. Extensive divergence of gene
content was observed, both between the B. oleracea paralogous segments and
between them and their homoeologous segment within the genome of Arabidopsi
s. However, the genes present show highly conserved collinearity with their
orthologues in the genome of Arabidopsis. We have identified one example o
f a Brassica gene in a non-collinear position and one rearrangement. Some o
f the genes not present in the discernible homoeologous regions appear to b
e located elsewhere in the B. oleracea genome. The implications of our find
ings for comparative map-based cloning of genes from crop species are discu
ssed.