Complex spatial and temporal expression of lipoxygenase genes during Phaseolus vulgaris (L.) development.

A new member (Lox1) of the lipoxygenase (LOX) gene family in French bean was isolated and its specific expression compared to the general expression pattern of related LOX genes. LOX transcripts detected by a French bean cDNA LOX probe were generally abundant in young, developing tissues, and LOX protein, detected on immunoblots showed a similar distribution. Tissue prints showed that cell-specific, locally high amounts of LOX protein were observed in some tissues, for example in parts of the starch sheath in the hypocotyl and a cell layer in the pericarp. The Lox1 gene from Phaseolus vulgaris was shown in genomic Southerns to be present as a single copy per haploid genome. RNase protection studies showed that the gene is active and the transcription start site was mapped by cDNA primer extension. RNase protection studies showed that Lox1 mRNA was present only in flowers and embryonic primary leaves, in stems and most strongly, in young secondary leaves but not in any of the other organs tested (i.e. not in roots, nodules, hypocotyls, cotyledons, older secondary leaves, pericarp or seeds). Lox1 gene transcripts did not accumulate in leaves in response to methyl jasmonate or pathogen inoculation, even though these treatments caused the accumulation of other LOX transcripts. Thus, the various lipoxygenase genes are regulated differentially during French bean development and in response to different stress stimuli, and possible functions are discussed in view of the specific expression patterns observed.