CDNA SEQUENCE, GENOMIC ORGANIZATION AND DIFFERENTIAL EXPRESSION OF 3 ARABIDOPSIS GENES FOR GERMIN OXALATE OXIDASE-LIKE PROTEINS

Wheat germin is a protein expressed during germination which possesses an oxalate oxidase activity. Germin-type oxalate oxidases have been e xtensively studied in monocotyledons (wheat and barley) where they are thought to have important functions for development, stress response and defence against pathogens. In contrast, almost nothing is known ab out the germin-like proteins found in dicotyledons, gymnosperms and my xomycetes. In this work, cDNA clones for three genes (ATGER1, ATGER2 a nd ATGER3) encoding germin-like proteins, initially characterized as e xpressed sequence tags (ESTs), from Arabidopsis thaliana cDNA librarie s were further characterized. In addition, we isolated and sequenced a Brassica napus cDNA which was strongly homologous to the cDNA for ATG ER1. Sequence analysis and secondary structure predictions of the prot eins encoded by these cDNAs showed that they possess all the character istic features of members of the germin family and of the germin/seed globulins/sucrose binding protein superfamily. Sequence comparisons an d mapping demonstrated the existence of at least two different gene fa milies in the A. thaliana genome encoding a minimum of three genes for germins. These three genes have been mapped in three different locati on on the Arabidopsis genome. By northern blot hybridizations we found that these genes are differentially regulated. ATGER1 was expressed d uring germination, like wheat germin, but also in leaves whereas ATGER 2 transcripts were exclusively found in developing embryos, like wheat pseudo-germin. ATGER3 mRNAs were found in leaves and flowers and thei r abundance was shown to vary during the circadian cycle.