Molecular cloning and characterization of SoNCED, a novel gene encoding 9-cis-epoxycarotenoid dioxygenase from sugarcane (Saccharum officinarum L.)

Abscisic acid (ABA) plays important roles in adaptive responses to various environmental stresses. The rate-limiting step in ABA biosynthesis is the oxidative cleavage of cis-epoxycarotenoids, which is catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED). In this experiment, a full-length cDNA encoding NCED gene was cloned by RT-PCR and RACE from sugarcane (Saccharum officinarum L.). The full-length of SoNCED is 2,521 bp with 1,827 bp open reading frame, encoding a peptide of 608 amino acids. The calculated molecular weight of protein was 65.9 kDa with isoelectric point of 6.04. Conserved domains prediction indicated a chloroplast-targeting peptide located at N-terminus of SoNCED. Phylogenetic tree, constructed by Neighbor-Joining method indicated that SoNCED shared high identity with the NCEDs reported from other plant species. Sequence alignment revealed that the basic secondary structure including α-helices, β-strands, β-propeller and His residues coordinating catalytic sites of SoNCED were highly conserved as in the NCEDs from other plants. Tissue specific expression analysis using quantitative real-time PCR showed a significant increase in SoNCED mRNA level and its correlation with O2 – production rate and ABA accumulation in leaves and roots of sugarcane variety GT21 when exposed to water stress. Further, the stimulation of SoNCED mRNA level, O2 – production rate and ABA content after exogenous application of ABA (100 μMol l−1) proved its involvement in pathways providing tolerance to drought stress.