APA locus identification and characterisation from common bean (Phaseolus vulgaris L.) BAC library.

Lectin and lectin-related seed proteins are encoded by a single locus, the APA locus, on linkage group 4 (Gepts 1999). In common bean this locus shows a high variability. In fact the three major lectin-related components are present all together only in some wild accessions, while most of the wild and cultivated P. vulgaris contain only phytohemagglutinin (PHA) and ?-amylase inhibitor (?-AI) and some wild Mesoamerican accessions contain only PHA and Arcelin (ARC). Our preliminary results confirm that the APA locus is very long, probably more than 250Kbp, in fact to cover the entire locus at least 4 overlapping clones will be needed. This result is in agreement with the finding of Kami et al. (2001), which analyzed the same locus in three different P. vulgaris genotypes. In addition, all our analyses suggest that PHA-E, ARC and PHA-L, besides being on the same locus, are more strictly associated to each other than ?-AI. To obtain a more detailed figure on the APA organization the sequencing of a first BAC clone containing a large part of the APA locus is in progress.