Phaseolin: Nucleotide Sequence Explains Molecular Weight and Charge Heterogeneity of a Small Multigene Family and also Assists Vector Construction for Gene Expression in Alien Tissue

Phaseolin: Structure and Evolution

“…The phaseolin data on domestication and dispersal of French bean cultivars was consistent with the existing archeological, botanical, historical and linguistic data (Gepts, 1988) [54]. This report, and that of Hall et al [36], initiated the use of molecular complexity to explain the value of a gene cluster and its product as a marker in crop evolution. Gepts [54] suggested that other seed proteins encoded by multi-gene families such as legumin and vicilin in pea, conglycinin and glycinin in soybean, zein in maize, B-hordein and amylase in barley can be explored from evolutionary aspects in a similar manner, as, indeed, can non-seed protein, and also other multi-gene proteins such as leghemoglobin, chlorophyll a/b binding protein and glutamine synthetase.…”

“…The number of copies of the phaseolin gene present in the genome remains somewhat ambiguous. Whereas reconstruction Southern blots indicated that 10-15 copies are present in Tendergreen, Sanilac and Contender cultivars [36], only 6-8 copies were predicted for Tendergreen genomic DNA from solution hybridization kinetics and genomic DNA blot hybridization [37]. The banding patterns obtained by single and two-dimensional gel electrophoretic analyses, indicate that Contender is a composite of Tendergreen and Sanilac types, showing a good agreement between the number of phaseolin protomers and structural genes.…”

“…Genetic analysis revealed a tight linkage for the entire phaseolin gene family [17]. Heteroduplex analysis of the phaseolin genomic clones [36] revealed that whereas the phaseolin DNA coding sequences were similar, considerable divergence occurred close to their 5' and 3' termini [37].…”

“…As the major seed storage protein of French bean, it accounts for 50% of the total protein stored in the cotyledons [36], and 35-46% of the total seed nitrogen [12,55]. It is now rigorously established that spatial regulation of phaseolin expression is mandated through a combination of epigenetic [56,57,58] and genetic [46] events (chromatin structure and transcription factors).…”

“…The divergence process included the insertions, duplications and deletions as demonstrated by the presence and absence of direct repeats [36,[60][61][62], and point deletions represented by nucleotide substitutions [33,36]. In addition to the divergence observed at the DNA level, co-and post-translational modifications, including signal peptide cleavage upon the polypeptide transit into the lumen of endoplasmic reticulum [35,36], glycosylation of polypeptides leading to variation in the polysaccharide side chains [34,35] and amino acid substitutions leading to charge differences [36] resulted in the formation of a group of similar, but slightly heterogeneous phaseolin polypeptides. The electrophoretic patterns of these molecular entities in terms of molecular weight and isoelectric point changes reflect genotypic divergence and have been widely used in analyzing evolutionary relationships among bean cultivars [54].…”