Crop improvement for human nutrition: the case of the Mexican yam bean [abstract]

The Mexican yam bean (Pachyrhizus erosus) is a tuberous legume native to Central America. This species shows great potential for development as a food crop, to increase the existing limited base of staples that make up the diet in tropical regions, producing both protein rich grain and starch producing tubers. Starch quality is good due to its high digestibility. The major limitation to its use as a staple crop, however, is the low starch content of the tubers. The low variability of the existing gene pool for the genus limits the use of conventional plant breeding for improvement of the crop. Genetic engineering for crop improvement is, therefore adopted. The molecular genetics of carbohydrate metabolism in tubers of the Mexican yam bean is being studied. The result of such studies will guide the application of genetic engineering technology to improve starch content of the tubers. The work reported here describes the cloning of putative genes for the large subunit of ADP-glucose pyrophosphorylase (Agp2) from yam bean tubers. A cDNA library was constructed from RNA isolated from two-month-old yam bean tubers. A probe for Agp2 was prepared by RTPCR analysis of the tuber RNA preparations, using degenerate primers. Four clones, which hybridized to the probe, were isolated for further characterization. (AU)