CHARACTERIZATION OF 2 MEMBERS OF THE ARABIDOPSIS-THALIANA GENE FAMILY, AT-BETA-FRUCT3 AND AT-BETA-FRUCT4 CODING FOR VACUOLAR INVERTASES

We have isolated and characterized two Arabidopsis thaliana cDNAs and their cognate genes, At beta fruct3 and At beta fruct4, encoding vacuo lar forms of invertase. Our sequencing results showed that the gene At beta fruct3 is located downstream of the 3-ketoacyl-acyl carrier prot ein synthase III gene (AtKasIII). At beta fruct3 and 4 are functional and organized into seven exons and six introns with an identical organ ization. The At beta fruct3 and At beta fruct4 genes encode, respectiv ely, polypeptides of 648 and 664 residues that contain all the charact eristic hallmarks of vacuolar invertases. A. thaliana is the first pla nt of which both cell-wall (At beta fruct1 and At beta fruct2) and vac uolar (At beta fruct3 and At beta fruct4) genes are characterized. The same number of exons and introns is seen in the genes At beta fruct1, At beta fruct3 and At beta fruct4 as well as in all other invertase g enes described to date. However, the position of the third intron is d ifferent in At beta fruct3 and At beta fruct4. At beta fruct2 shows a different organization. A neighbour-joining distance tree shows that t he A, thaliana vacuolar invertases described here are, as expected, mo re closely related to vacuolar invertases from other plant species (e. g., carrot) than to the A. thaliana cell-wall invertases. The evolutio n of plant invertase genes from a common ancestral gene is discussed. Our results demonstrate that in A. thaliana, at least two genes encodi ng vacuolar invertases are expressed during the development of the pla nt. Southern blot hybridization experiments suggest the presence of on e copy of, respectively, At beta fruct3 and At beta fruct4 per haploid genome, and Northern blot analysis demonstrates that vacuolar inverta se genes are highly expressed in stems, roots, flowers and at very low levels in mature leaves. (C) 1997 Elsevier Science B.V.