Analysis of maturation-specific genes in soybean seeds: Gene structure, desiccation induction and abscisic acid responsiveness

This study describes two maturation (Mat) genes which share some structural similarities with a special group of genes, whose expression can be induced by water stress and also by exogenous abscisic acid (ABA) application. Previous studies have identified a 31-kDa maturation polypeptide (MAT) which accumulates during normal and precocious maturation of soybean (Glycine max L. Merr) seeds, and disappears rapidly during germination. The corresponding mRNA can also be induced in germinating seeds with ABA treatment, but not in normally developing seeds. By screening a 65 day-after-flower (DAF) seed cDNA library with a partial cDNA clone corresponding to the 31 kDa MAT protein, we were able to isolate and characterize two closely-related gene sequences represented by the pMat1 and pMat9 clones. Primer extension studies indicated that these two clones were full length cDNA clones. In the soybean genome, we identified at least two copies of the Mat1 genes and one Mat1-related gene, probably the Mat9 gene, in both the Williams'82 and T157 varieties. The nucleotide sequence comparison of cDNA and genomic clones showed these Mat genes do not contain any introns, which was confirmed by polymerase-chain-reaction (PCR) analysis of soybean seed mRNA and genomic DNA. The pMat 1 and pMat9 clones not only differ in size (51 nucleotides less in the coding region of pMat9 than in the coding region of pMat1), but the corresponding genes also differ in their expression patterns during normal and precocious maturation stages, and also by differential response to exogenous abscisic acid during germination. The protein sequence analysis showed that MAT proteins contain a highly conserved C-terminal region, which is also present in rice RAB (ABA-responsive) proteins and also in the cotton LEA and barley dehydrin proteins. The N-termini of MAT proteins also contains a short 7-amino acid stretch which might be related to the tissue-specificity expression or activity of these proteins. Possible roles of MAT proteins in seed maturation processes are discussed.U of I OnlyETDs are only available to UIUC Users without author permissio