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

Abstract

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.

Regulation of storage protein gene expression inArabidopsis

“…Their regulation might, however, differ slightly from one SSP gene to another because the effects of single mutations on individual genes are not identical. At2S1, for example, is less affected by fus3 or lec2 single mutations than other At2S genes, probably because At2S1 is specifically expressed in the embryonic axis (Guerche et al, 1990) where the effects of the fus3 and lec2 single mutations are the weakest (as judged by At2S3 expression).…”

“…We wondered whether other SSP genes are regulated in the same way as At2S3. In order to test this, we designed specific probes for four At2S genes and three cruciferin genes (Guerche et al, 1990;Pang et al, 1988) and analysed SSP gene expression in abi3, fus3, lec2 and lec2 fus3 mutants. We found that the expression of all genes was reduced to a variable extend in fus3 and lec2 single mutants but drastically reduced in lec2 fus3 (Fig.…”

“…As in other brassicaceae, seeds of the model plant Arabidopsis thaliana mainly accumulate lipids and storage proteins (Mansfield and Briarty, 1992). 2S and 12S proteins are the major seed storage proteins (SSP) and represent up to one third of the Arabidopsis seed's dry weight (Baud et al, 2002;Guerche et al, 1990;Pang et al, 1988). SSP genes are highly expressed and tightly regulated both spatially and temporally.…”

Gene expression during plant embryogenesis and germination: an overview.

“…The expression patterns of seed protein genes are highly regulated spatially and temporally during seed development Perez-Grau and Goldberg, 1989;Guerche et al, 1990), and resulting storage proteins are processed and targeted to protein bodies (Shotwell and Larkins, 1989). The tissue-specific expression of seed protein genes during seed development has made them especially useful as models of gene expression in embryogenesis, and as a consequence, there have been extensive studies on the structure and expression of these genes from numerous plant species.…”

A cotyledon regulatory region is responsible for the different spatial expression patterns of Arabidopsis 2S albumin genes

“…The siliques for RNA extraction were harvested during the developmental stages when the expression of endogenous Arabidopsis 2S albumins is highest (between stages D and E, as defined by Guerche et aL, 1990). Total RNA from siliques was extracted and used in slot-blot analysis as described previously .…”