Seed-specific expression patterns and regulation by ABI3 of an unusual late embryogenesis-abundant gene in sunflower

We cloned the genomic sequences that correspond to a previously described g roup 1 late embryogenesis-abundant (Lea) cDNA from sunflower: Ha ds10. The Ha ds10 G1 gene had structural and gene-expression features that depart fro m those of other group 1 Lea genes. An intron was present at a conserved po sition but showed a much larger size (1024 bp). Transcription from the Ha d s10 G1 promoter was strictly seed-specific and it originated from at least two close initiation sites. The mRNAs accumulated from stages of embryogene sis that preceded seed desiccation. Ha ds10 G1 mRNA accumulation was modera tely induced, by exogenous abscisic acid treatments, in immature seeds but not induced in seedlings. We observed unprecedented changes in Lea mRNA loc alization associated with seed desiccation: the homogeneous tissue distribu tion of Ha ds10 G1 mRNAs, which was characteristic of immature embryos, evo lved later in embryogenesis to an asymmetric distribution within the cotyle dons, with preferential mRNA accumulation in the cells of the palisade pare nchyma and provascular bundles. We also showed that, in sunflower embryos, the Ha ds10 G1 promoter could be transiently activated by the Arabidopsis A BI3 transcription factor. We discuss the significance of these results rega rding hypotheses of regulation and function of plant genes from the same fa mily.