Abstract: Alanine Aminotransferase (AlaAT) is a critical enzyme involved in carbohydrate and nitrogen metabolisms. In this study, a cDNA (1 747 bp) with a complete ORF (1 626 bp) of AlaAT1 was isolated from tea plant (Camellia sinensis). The cDNA encodes a protein with 541 amino acids, which has a molecular mass of 59.4 kD and a theoretical isoelectric point (pI) of 5.82. The deduced sequence of protein CsAlaAT1 shared 84% similarity with AlaAT1 in Arabidopsis thaliana, which contains a highly-conserved pyridoxal 5′-phosphate binding site. Secondary structure prediction showed that the CsAlaAT1 was comprised of alpha helix (40.67%), random coil (29.57%), beta turn (13.68%) and extended strand (16.08%), localized in mitochondrion and had no signal peptide or transmembrane structure. The expression levels of CsAlaAT1 in various tissues and its responses to different N concentration were investigated by real-time fluorescent quantitative RT-PCR. The results of RT-PCR showed that CsAlaAT1 expressed in all tissues of tea plant and the highest transcript level was observed in roots. The transcript abundance of CsAlaAT1 was up-regulated by N in both shoots and mature leaves, especially under high N condition. Interestingly, the expression of CsAlaAT1 in roots was highly induced high N condition, but showed an opposite trend under low N treatment for 24 h.

Key words: tea plant (Camellia sinensis), Alanine aminotransferase, cloning, expression, nitrogen induction