|Kottapalli, Kameswara Rao|
Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2008
Publication Date: 9/1/2008
Citation: Kottapalli, K., Payton, P., Rakwal, R., Agrawal, G., Shibato, J., Burow, M., Puppala, N. 2008. Proteomics analysis in mature seed of four peanut cultivars using two-dimensional gel electrophoresis reveals distinct differential expression of storage, anti-nutritive, and allergenic proteins. Plant Science. 175(3):321-329. Interpretive Summary: Peanut (Aracghis hypogaea L.) is the third-most important source of plant protein, contributing 11% of world’s protein supply. Grown for its seed in the USA, peanut represents a rich source of edible fats and a primary source of oil in many parts of the world. In the United States, cultivated peanuts are classified into four major market types: Runner, Virginia, Spanish, and Valencia. The Runner market type predominates in the Southeast (Georgia, Florida, Alabama and South Carolina) and Southwest (Texas, Oklahoma, and New Mexico). The Virginia market types predominate in the Virginia-North Carolina (VC) region., Although runner peanuts comprise the majority of peanut acreage in the Southwest, significant quantities of Spanish and Valencia are also cultivated in the region. Runner and Virginia market types belong to subspecies hypogaea var. hypogaea whereas the Valencia and Spanish market type belongs to subsp. fastigiata var. fastigiata and subsp. fastigiata var. vulgaris, respectively. At present, the runner market type occupies 84% of the total peanut acreage in the United States followed by Virginia (13%), Spanish (2%) and Valencia (1%) market types.2 Among runner market types, Georgia Green is the most widely-grown cultivar because of its resistance to Tomato Spotted Wilt Virus (TSWV). This single cultivar occupies 66% of the runner market and 55% of the US market. The cultivar NC-7, a Virginia type, occupies 6.4% of the Virginia market and less than 1% of all US market. The cultivar Tamspan 90, a Spanish type, occupies 64% of the Spanish market and about 2% of the US market. The cultivars NM Valencia-A and C, belonging to Valencia group occupy 99% of the Valencia market. Valencia peanuts constitute a niche crop for eastern New Mexico and are known for their superior taste and having three or more seeds per pod. Numerous studies on peanut seed proteins emphasized storage protein composition, nutritional value, and immunological properties of the protein fractions. However, key metabolic pathways and mechanisms of differential accumulation of various protein components that result in differences in seed morphology and quality (taste, allergenicity) remain largely unknown. A better understanding of the function of proteins expressed in mature seeds might help not only in cultivar differentiation, but also in improving the nutritional value of the peanut seed. Here we have optimized a 2-dimensional gel electrophoresis (2-DGE) proteomics approach for peanut seed as a first step in our quest to establish comprehensive seed proteomes of different peanut cultivars. In this study, 2-DGE-based proteomics was applied to four peanut cultivars: New Mexico Valencia C, Tamspan 90, Georgia Green, and NC-7, in order to identify proteins unique to each, and elucidate potential factors underlying the differences in seed attributes among major market types. Out of 20 differentially expressed proteins (either distinctly present and/or absent or quantitatively variable) among the four cultivars, 14 non-redundant proteins were identified by nano-electrospray ionization liquid chromatography tandem mass spectrometry (nESI-LC-MS/MS). The majority of these proteins belonged to the globulin fraction of seed proteins. We believe that these proteins could be used to distinguish these popular peanut cultivars representing the four US peanut market types. It is also likely that some of these proteins may be associated with the basic differences in sensory attributes and nutritional traits including allergens in these cultivars.
Technical Abstract: Protein profiles of total seed proteins isolated from mature seeds of four peanut cultivars, New Mexico Valencia C (NM Valencia C), Tamspan 90, Georgia Green, and NC-7, were studied using two-dimensional gel electrophoresis coupled with nano electrospray ionization liquid chromatography tandem mass spectrometry (nESI-LC-MS/MS). Two-dimensional gels stained with silver nitrate revealed a total of 457, 516, 556, and 530 protein spots in NM Valencia C, Tamspan 90, Georgia Green, and NC-7, respectively. Twenty abundant protein spots differentially expressed among these cultivars were analyzed by nESI-LC-MS/MS, resulting in identification of 14 nonredundant proteins. The majority of these proteins belonged to the globulin fraction consisting of arachin (glycinin and Arah3/4) and conarachin seed storage proteins as well as other allergen proteins. The expression of some of these identified protein spots were cultivar-specific. For example, allergen Arah3/Arah4 and conarachin protein spots were only detected in Tamspan 90 and NC-7, whereas the Gly1 protein spot was detected only in NM Valencia C and NC-7. Moreover, a galactose-binding lectin protein spot with antinutritive properties was only present in Tamspan 90. Other proteins that were expressed differentially in these four cultivars were 13-lipoxygenase, fructose-biphosphate aldolase, and glyceraldehyde 3-phosphate dehydrogenase. Together, these results suggest that identified proteins might serve as potential markers for cultivar differentiation and may be associated with underlying sensory and nutritional traits of peanut cultivars.