CRUCIFERIN GENE FAMILIES ARE EXPRESSED COORDINATELY BUT WITH TISSUE-SPECIFIC DIFFERENCES DURING BRASSICA-NAPUS SEED DEVELOPMENT

The major storage protein in seeds of Brassica napus, the 12S globulin cruciferin, is composed of three different groups of subunits; cru1, cru2/3 and cru4. By using gene family-specific probes, we have investi gated the accumulation, rate of synthesis and spatial distribution of transcripts corresponding to the different groups of cruciferin subuni ts in developing seeds. Cruciferin transcripts derived from different gene families accumulate coordinately to comparable amounts during see d development. The corresponding gene families are, however, transcrib ed at different rates. Investigation of the spatial distribution of tr anscripts corresponding to each group of cruciferin subunits in the de veloping seed by in situ hybridization, revealed that mRNAs of all thr ee types accumulate in both axis and cotyledons. Transcripts derived f rom cru1 and cru4 gene families show a similar cell specificity and ac cumulate in a similar spatial manner during seed development. In contr ast, mRNAs corresponding to the cru2/3 gene family are expressed with a partly different cell specificity and show a slightly different patt ern of accumulation in the axis and cotyledons, with a delayed accumul ation in epidermal cells. In the cotyledons, the initial accumulation of this type of cruciferin mRNAs is also distinguished from the two ot her types. The differences in cell specificity are seen in the root ca p and in provascular cells, where mRNAs belonging to the cru2/3 family are absent.