Isolation and characterization of the Agmt2 gene and its response to abiotic and metalstress in Apium graveolens

Metallothioneins (MTs) are defined as small cysteine-rich, metal-binding proteins. In this study, the Agmt2 genes were cloned from three celery cultivars 'Liuhe Huangxinqin', 'Jinnan Shiqin' and 'Ventura', respectively. The Agmt2 gene showed a length of 231 bp open reading frame (ORF) and encoded with 76 amino acid residues, with two introns of 385 bp. Sequence analysis indicated that AgMT2 belonged to the Metallothio_2 superfamily. The predicted molecular weight and pI value of the AgMT2 protein were 7.5 kD and 4.95 respectively. There was one change in nucleotide acid site in 'Liuhe Huangxinqin' compared to 'Jinnan Shiqin' and 'Ventura'. The amino acid sequences of AgMT2 in three cultivars were completely identical. Multiple sequence alignment showed that domain of MT2-like proteins was highly conserved. AgMT2 further demonstrated a very close evolutionary relationship with MT2 from Nicotiana tomentosiformis, Nicotiana sylvestris and Nicotiana Plumbaginifolia in Solanaceae. Quantitative RT-PCR revealed that Agmt2 gene expression profiles exhibited tissue specificity in celery. Agmt2 gene expression responsed more significant in 'Ventura' than in 'Liuhe Huangxinqin' and 'Jinnan Shiqin' under eight metal ions (Co2+, Ni2+, Fe2+, Mg2+, Ca2+, Cu2+, Zn2+) and four abiotic stress treatments (hot, cold, salt and drought). Our findings served as a valuable resource for AgMT2 protein in celery.