DISTINCT ANNEXIN SUBFAMILIES IN PLANTS AND PROTISTS DIVERGED PRIOR TOANIMAL ANNEXINS AND FROM A COMMON ANCESTOR

(A)nnexin homologues in the kingdoms of Planta and Protista were chara cterized by molecular sequence analysis to determine their phylogeneti c and structural relationship with annexins of Animalia. Sequence frag ments from 19 plant annexins were identified in sequence databases and composite sequences were also assembled from expressed sequence tags for Arabidopsis thaliana. Length differences in protein amino-termini and evidence for unique exon splice sites indicated that plant annexin s were distinct from those of animals. A third annexin gene of Giardia lamblia (Anx21-Gla) was identified as a distant relative to other pro tist annexins and to those of higher eukaryotes, thus providing a suit able outgroup for evolutionary reconstruction of the family tree. Root ed evolutionary trees portrayed protist, plant, and Dictyostelium anne xins as early, monophyletic ramifications prior to the appearance of c losely related animal annexin XIII. Molecular phylogenetic analyses of DNA and protein sequence alignments revealed at least seven separate plant subfamilies, represented by Anx18 (alfalfa, previously classifie d), Anx22 (thale cress), Anx23 (thale cress, cotton, rape and cabbage) , Anx24 (bell pepper and tomato p34), Anx25 (strawberry, horseradish, pea, soybean, and castor bean), Anx26-Zma, and Anx27-Zma (maize). Othe r unique subfamilies may exist for rice, tomato p35, apple, and celery annexins. Consensus sequences compiled for each eukaryotic kingdom sh owed some breakdown of the ''annexin-fold'' motif in repeats 2 and 3 o f protist and plant annexins and a conserved codon deletion in repeat 3 of plants. The characterization of distinct annexin genes in plants and protists reflects their comparable diversity among animal species and offers alternative models for the comparative study of structure-f unction relationships within this important gene family.