Structural relationship among the members of a multigene family coding for the sweet potato tuberous root storage protein

Abstract

Sporamin, the major soluble protein of the sweet potato tuberous root, is coded for by a multigene family. Fourty-nine essentially full-length sporamin cDNAs isolated from tuberous root cDNA library have been classified by cross hybridization, restriction endonuclease cleavage pattern and ribonuclease cleavage mapping. All the cDNAs fall into one of the two distinct homology groups, subfamilies A and B, which correspond to the polypeptide classes sporamin A and B, respectively. At least 5 different sequences are detected in both of the 22 sporamin A and 27 sporamin B cDNAs. Comparison of the nucleotide sequences of the coding region of three each of sporamin A and B subfamily members, four from cDNAs and two from genomic clones, indicates that intra-subfamily homologies (94 to 98%) are much higher than inter-subfamily homologies (82 to 84%), and there are deletions or insertions of one or two codons at three locations which characterize each subfamily. Large portions of base substitutions in the coding region accompany amino acid substitutions. In contrast to the coding region, most of the structural differences among the members in the 5' and 3' noncoding regions are deletions or insertions.

Negative Regulation in the Expression of a Sugar-Inducible Gene in Arabidopsis thaliana (A Recessive Mutation Causing Enhanced Expression of a Gene for β-Amylase)

“…In leaves of sweet potato, the sugar-induced accumulation of P-amylase occurs in mesophyll cells in addition to vascular tissue (Takeda et al, 1995). It occurs concomitantly with the accumulation of starch and sporamin, a tuber storage protein with homology to wound-inducible trypsin inhibitors (Hattori et al, 1989;Bradshaw et al, 1990). Furthermore, accumulation of sporamin and p-amylase was also induced by polygalacturonic acid and by ABA (Ohto et al, 1992;Takeda et al, 1995).…”

Induction of Expression of Genes Coding for Sporamin and β-Amylase by Polygalacturonic Acid in Leaf-Petiole Cuttings of Sweet Potato

“…Sporamin is encoded by a multigene family (11,17), and a hexaploid genome of the sweet potato contains a total of about 60 copies of sporamin genes (Y. Kowyama, T. Hattori, T. Kumashiro, and K. Nakamura, unpublished data). By contrast, ,3-amylase is encoded by a gene that is present as a single-copy per haploid genome (28).…”

Propeptide of a precursor to a plant vacuolar protein required for vacuolar targeting.

“…Sporamin is a storage protein found in the tuberous roots of sweet potato (Ipomoea batatas) (22), and it is a mixture of closely related polypeptides encoded by a multigene family composed of two major subfamilies, A and B (22,23). It is accumulated in the vacuoles of parenchymatous cells as a nonglycosylated monomeric protein.…”