Differential Expression of the Arabidopsis 2S Albumin Genes and the Effect of Increasing Gene Family Size.

We studied the expression of the four genes encoding 2S albumin seed storage proteins (at2S1 to at2S4) in Arabidopsis thaliana. All four genes followed similar temporal profiles throughout development, but at2S2 and at2S3 were expressed at significantly higher levels than at2S1 or at2S4. In situ hybridization showed that at2S2 to at2S4 mRNAs were present throughout the embryo, whereas at2S1 was expressed at levels similar to at2S2 and at2S3 in the embryo axis but at only insignificant levels in the cotyledons. The different members of the gene family are, thus, likely to be regulated by different combinations of cis-acting elements, but it cannot be ruled out that post-transcriptional factors play a role. We studied the effect of enlarging the gene family by introducing an extra, nearly identical gene driven by the promoter of at2S1. The data were consistent with a model in which the expression of at2S2 to at2S4 is not affected by that of at2S1, and in which, at least at low copy numbers of the introduced gene, there is no limit on the overall amount of RNA that the at2S gene family can produce.