Plant Genome III Conference Plant Genome III Conference
The Leguminosae (Fabaceae) include 650 genera and 18,000 species and represent the third largest family of flowering plants. One of the three subfamilies of the family, the Papilionoideae, contains about 440 genera and 12,000 species. This subfamily is particularly important in agriculture and will be the focus of this presentation. Within the Papilionoideae there are at least 60 genera of economic importance. For comparative mapping purposes, these genera may be placed into six groups: (1) those related to Phaseolus, (2) those related to Trifolium, (3) those related to Pisum, (4) Arachis and its relatives, (5) Lupinus and its relatives, (6) isolated genera of minor economic importance. Groups I and 4 are primarily of tropical origin, whereas groups 2, 3, and 5 are temperate. Genomes of group I taxa are usually small to very small (e.g. Vigna radiata). In contrast, group 3 plants have large genomes, of comparable complexity to that of the human. Group 2 taxa possess genomes of intermediate size but exhibit very short genetic maps (300- 600 cM). Comparative mapping studies by several investigators have revealed considerable conservation of gene linkage arrangement within group 1 (particularly within the Phaseolus/Vigna complex) and within group 3. The chickpea map displays about 40% linkage conservation with the pea map, suggesting some homology will exist between the linkage maps of groups 2 and 3 despite the major differences in DNA content and map size. At present there has been only one indication of linkage conservation between groups 1 and Linkage maps of group 4 taxa are just beginning to be compared with those of the other groups, and a Lupinus map is still in the formative stage. However, as these latter groups are not closely related to any of the first three, it is unlikely that high conservation of linkage groups will be demonstrated. At least at this early stage of comparison, there appears to be considerable rearrangement of linkage groups among Papilionoid tribes. No one genus will be able to serve as a model. However, within tribes, prediction of linkage arrangements based on a well studied model may be highly successful.