Identifying the determinants of high protein content in seeds of Phaseolus vulgaris

The first farmers initiated the process of domestication of present day crops approximately 8 to 12,000-years ago by selecting plants with desirable traits from ancestral wild populations. During the domesticatin of common bean these traits included, among others, increased seed size, which increased yield and productivity due to a five- to eight-fold increase in seed weight.

The increase in seed weight was associated with an increase in the relative starch content at the expense of protein content, perhaps explained by the fact that it is energetically less expensive for the plant to fill the large seeds with starch than with protein. It appears that early-farmers inadvertently selected for genes that can synthesize high levels of seed starch, along with genes that make larger seeds.

With a focus on improving protein content, this project examines the basic molecular underpinnings of how starch and protein content is varied. Understanding how the balance of protein to starch is regulated during seed development will help explain how this important traits are controlled. Genes that control the relative content of starch and protein in common bean seeds will be identified by comparing developmental expression in wild and domesticated varieties.

Knowledge about these genes and the mechanism by which they operate could help us improve the protein and nutritional content of present day beans through genetic manipulation. During the research, high school teachers will gain lab experience and will contribute to the development of high school teaching modules in quantitative development Two graduate students will be trained on the latest biological and technological approaches and procedures applicable to this project.

Domestication of seed crops resulted in seed size and yield increases. These gains were attained through increases in relative starch content at the expense of protein accumulation. Although on a dry weight basis starch and protein have the same caloric content, protein biosynthesis is several-fold more metabolically expensive than starch biosynthesis.

Increases in relative starch content are correlated with decreases in relative protein content because the biosynthesis of these polymers draws from the same carbon pool. The main objective of this proposal is to identify key determinants of the strength of protein and starch sinks in seeds of Phaseolus vulgaris. This objective will be accomplished through a comparative analysis of evolutionary changes that separated the Andean from the Mesoamerican gene pool, and cultivated forms from their wild ancestors in each pool.

Phenotypic and gene expression differences will be evaluated in the context of a developmental index based on mathematical descriptions of seed/pod growth and development. Genes with a differential pattern of expression that is correlated with phenotypic differences will be subjected to genetic analysis to identify genes responsible for phenotypic differences.

The nutritional value of beans and other legumes could be improved after the identification of genes that control protein and starch sink strength in the seed. In addition, increasing seed protein content will help increase the reliance of human diet on plant-based protein because animal protein production is associated with environmental degradation.

The educational component of this project includes the training of two graduate students, two high school teachers and the public at large.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.