Résumé
We have isolated and characterized two
Arabidopsis thaliana cDNAs and their cognate genes,
Atβfruct3 and
Atβfruct4, encoding vacuolar forms of invertase. Our sequencing results showed that the gene
Atβfruct3 is located downstream of the 3-ketoacyl-acyl carrier protein synthase III gene (
AtKasIII).
Atβfruct3 and
4 are functional and organized into seven exons and six introns with an identical organization. The
Atβfruct3 and
Atβfruct4 genes encode, respectively, polypeptides of 648 and 664 residues that contain all the characteristic hallmarks of vacuolar invertases.
A. thaliana is the first plant of which both cell-wall (
Atβfruct1 and
Atβfruct2) and vacuolar (
Atβfruct3 and
Atβfruct4) genes are characterized. The same number of exons and introns is seen in the genes
Atβfruct1,
Atβfruct3 and
Atβfruct4 as well as in all other invertase genes described to date. However, the position of the third intron is different in
Atβfruct3 and
Atβfruct4.
Atβfruct2 shows a different organization. A neighbour-joining distance tree shows that the
A. thaliana vacuolar invertases described here are, as expected, more closely related to vacuolar invertases from other plant species (e.g., carrot) than to the
A. thaliana cell-wall invertases. The evolution of plant invertase genes from a common ancestral gene is discussed. Our results demonstrate that in
A. thaliana, at least two genes encoding vacuolar invertases are expressed during the development of the plant. Southern blot hybridization experiments suggest the presence of one copy of, respectively,
Atβfruct3 and
Atβfruct4 per haploid genome, and Northern blot analysis demonstrates that vacuolar invertase genes are highly expressed in stems, roots, flowers and at very low levels in mature leaves.