Characterization of a Proline-rich Cell Wall Protein Gene Family of Soybean

Further characterization of a proline-rich cell wall protein gene family from soybean (Glycine max (L.) Merr) has been accomplished by the isolation and sequence analysis of two additional genes, SbPRP2 and SbPRP3, which encode mRNAs of 1050 and 650 nucleotides in length, respectively. Like the proline-rich protein gene, SbPRPl, which was previously reported (Hong, J. C., Nagao, R. T., and Key, J. L. (1987) J. Biol. Chem. 262,8367-8376), these two SbPRP genes encode proteins having a signal peptide sequence and repeats of Pro-Pro-Val-Tyr-Lys. The SbPRP2 gene encodes a protein of 26 kDa which contains a perfect alternating repeat of Pro-Pro-Val-Tyr-Lys and ProPro-Val-Glu-Lys. The SbPRP3 encodes a lo-kDa protein which also contains Pro-Pro-Val-Tyr-Lys as a major amino acid repeat, but the overall amino acid sequence of this protein is more variable than that of SbPRPl and SbPRP2. RNA blot analyses have demonstrated that there are marked differences in the pattern of expression of each SbPRP in various soybean tissues. In contrast, sequence analysis reveals that the SbPRP genes contain a high degree of sequence conservation. Nucleotide sequence homology extends 90 to 100 base pairs upstream of the transcription initiation site and includes typical CAT and TATA sequences. Approximately 80 base pairs of the 3’-noncoding sequence around the polyadenylation signal is also highly conserved. Therefore, the DNA sequence upstream of the 5’-conserved region is presumed to contain c&elements accounting for the developmental and tissue specificity of gene expression. While the pentameric repeat structures occur in all SbPRP genes, the encoded proteins are predicted to be different in several features including basicity, substitutions of tyrosine and glutamic acid in the repeat, and the size of the mature protein.