DEVELOPMENTAL CONTROL OF H+ AMINO ACID PERMEASE GENE-EXPRESSION DURING SEED DEVELOPMENT OF ARABIDOPSIS/

Long distance transport of amino acids is mediated by several families of differentially expressed amino acid transporters. The two genes AA P1 and AAP2 encode broad specificity H+-amino acid co-transporters and are expressed to high levels in siliques of Arabidopsis, indicating a potential role in supplying the seeds with organic nitrogen. The expr ession of both genes is developmentally controlled and is strongly ind uced in siliques at heart stage of embryogenesis, shortly before induc tion of storage protein genes. Histochemical analysis of transgenic pl ants expressing promoter-GUS fusions shows that the genes have nonover lapping expression patterns in siliques. AAP1 Is expressed in the endo sperm and the cotyledons whereas AAP2 is expressed in the vascular str ands of siliques and in funiculi. The endosperm expression of AAP1 dur ing early stages of seed development indicates that the endosperm serv es as a transient storage tissue for organic nitrogen. Amino acids are transported in both xylem and phloem but during seed filling are impo rted only via the phloem. AAP2, which is expressed in the phloem of st ems and in the veins supplying seeds, may function in uptake of amino acids assimilated in the green silique tissue, in the retrieval of ami no acids leaking passively out of the phloem and in xylem-to-phloem tr ansfer along the path. The promoters provide excellent tools to study developmental, hormonal and metabolic control of nitrogen nutrition du ring development and may help to manipulate the timing and composition of amino acid import into seeds.