Expression of Asr genes during embryogenesis and cellular localization of transcripts upon water stress in vegetative organs

FRANKEL N; MASKIN L; MALDONADO S; IUSEM N

Bariloche, Rio Negro, Argentina

Congreso; XXXIX Reunión anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB); 2003

Asr genes of tomato are a family of putative transcription factors up-regulated during water-stress. Several homologues have been cloned from different plant species, but little is known about these genes. Recently, an Asr from grape has been shown to activate an hexose transporter promoter. In this work, we analyze the pattern of expresion of Asr1 and Asr2 during embryogenesis and investigate the cellular localization of the transcripts in roots and leaves under normal and stress conditions. Both proteins are detected only in late embryogenesis (55-70 days post-anthesis). This expression correlates with the lowest seed water content and the accquisition of dessication tolerance. However, ASR proteins lack any of the known late embryogenesis abundant (LEA) protein motifs. In situ hibrydization assays showed that Asr1 and Asr2 are specifically transcribed in companion cells of the leaf phloem under normal conditions. Upon water-stress, Asr1 and Asr2 presence expands to surrounding parenchima cells. Asr1 mRNA was not detected in roots under both normal and stress conditions. In contrast, Asr2 mRNA is present in root phloem under water-stress treatment. According to our preliminary results, tomato ASR proteins may form heterodimers or homodimers in their native state.