Two soybean seed lipoxygenase nulls accumulate reduced levels of lipoxygenase transcripts

Soybean (Glycine max L. [Merrill]) seed lipoxygenase cDNA clones were recovered from two cDNA libraries: a size-selected library in pBR322 and an expression library in pUC8. The pUC8 library was made with total poly(A)⁺ embryo RNA and was screened with antiserum to lipoxygenase-1, one of 3 seed lipoxygenase isozymes. Three lipoxygenase antigen-producing clones were identified: two with identical cDNA inserts of 977 nucleotides representing an open-reading frame and a third truncated clone bearing a 3′ end common to the longer clones. A long clone, pAL-134, was chosen for further study and was used to screen the size-selected cDNA library from which sixteen clones were identified. They fall into two homology classes represented by pLX-10 (ca. 1360 bp) and pLX-65 (2047 bp). The lipoxygenase expression clone pAL-134 hybridized much more strongly to pLX-65 than to pLX-10. pAL-134 and pLX-65 share 89% nucleotide homology and 75% deduced amino acid homology along their common sequence. Their deduced amino acid sequences each show 80% homology to sequences determined for isolated peptides of the lipoxygenase-1 isozyme. pAL-134 hybridizes poorly with a 3.8 kb RNA from LOX-1 null (lx1) embryos while pLX-65 hybridizes more strongly, but still to a lesser extent than its hybridization to standard embryo RNA or to RNA from embryos lacking lipoxygenase-2 (lx2) or lipoxygenase-3 (lx3) protein. The lx3 null lacks almost all embryo 3.8 kb RNA homologous to pLX-10. This hybridization pattern suggests that pLX-10 encodes LOX-3. Thus, the lx1 and lx3 genotypes accumulate little, if any, mRNA for the lipoxygenase-1 and lipoxygenase-3 isozymes, respectively.