TISSUE-SPECIFIC EXPRESSION OF ATCYS-3A, A GENE ENCODING THE CYTOSOLICISOFORM OF O-ACETYLSERINE(THIOL)LYASE IN ARABIDOPSIS

Atcys-3A from Arabidopsis encodes the cytosolic isoform of O-acetylser ine(thiol)lyase that catalyzes the last step of cysteine biosynthesis. The Arcys-3A transcript is present in different organs of mature plan ts, being more abundant in roots and declining to 40-50% in rosette le aves and flowers. In situ hybridization studies have shown a high Arcy s-3A signal in root tissues, mainly localized to the cortex and xylem parenchyma. In a flower before anthesis, the transcript is detected ex clusively in anthers and sepals and evenly distributed throughout the receptacle of the flower. An unexpected observation from these studies is the highest expression of Atcys-3A mRNA found in trichomes of eith er leaf or stem. The presence of high levels of the transcript is obse rved very early in trichome cell development. This is the first report describing the cellular localization of any plant O-acetylserine(thio l)lyase mRNA. The high level of Atcys-3A expression in trichomes raise s new aspects to the biological function of trichomes, related to sulf ate metabolism.