Molecular Modeling Of AtNAC1Transcription Factor And Expression Analysis Of NAC Family Genes From Dendrobium Candidum Wall. Ex Lindl

NAC is a plant-specific transcription factor family, which was involved in the physiological processes of growth development, signal transduction, stress response. Arabidopsis thaliana AtNAC1transcription factor is involved the signal pathway of phytohormone and plays an important role in the regulation of root growth development. As a transcription factor, AtNAC1recognizes the target DNA element to regulate the expression of downstream gene. In order to understand the transcriptional control, an important direction is to understand its molecular structure and DNA bindding mode.The study analyzed the structure and DNA bindding mode of AtNACl by molecular modeling, docking and dynamic simulation. The main conclusions were shown as bellow. The structure of AtNAC1contained4α-hlices and8β-sheets; two AtNAC1monomers formed a homodimer by the N-terminal β-sheet, residue Arg24and residue Glu31. AtNAC1bound with DNA by inserting the β-sheet cotaining WKATGKDR motif into the major groove of DNA. The binding sites in DNA were5’-CTGACGTA-3’and5’-GATGACGC-3’. Residues Lysl02, Alal03, Thrl04, Glyl05, Lysl06and Aspl07binding with the bases of DNA might be responsible for recognizing DNA site, while Arg91, Lysl35and Lysl71might be responsible for affinity with DNA. The study provided the in silico framework to understand the interactions of AtNAC1with DNA at the molecular level.Seed embryo of Dendrobium candidum possesses the Orchidaceae-specific development mode, which body plan is constructed with protocorm development. Recent study indicated that some NAC members showed differential expression in development of somatic embryo protocorm and seed embryo protocorm, which indicted that NAC might play an important role in protocorm development. It is not clear how many NAC members involved in protocorm development and their regulation regulation is unkown.After molecular cloning and sequence analysis of D. candidum NAC family, the obtained NAC members were subjected to quantitative expression analysis during protocorm development. The main conclusions are shown as bellow. Thirty sequences of NAC CDS were obtained. Length of NAC proteins was between172-958residues. Most NAC proteins have N-terminal NAC domain and C-terminal transcriptional regulatory domain. Most N-terminal NAC domains have typical A/B/C/D/E subdomains. Some NAC proteins have specific structures, such as missing A subdomain, extra N-terminal region, missing C-terminal region, hydrophobic motif in the medial sequence, extra C-terminal region, C-terminal transmembrane domain, etc. Most NAC proteins have simple repetitive sequences, which length were between3-8residues. The phylogenesis analysis of D. candidum NAC proteins and other NAC proteins showed that NAC proteins were divided into9groups (A～I). Group A and H were related to the formation of organ boundary and meristem, flowering, and cell division. Group B and C might be inolved in the development of root and secondary growth, respectively. Group E was mostly related to abiotic and biotic stress. Group F and I might be inolved in regulation of phytohormone and mineral element, senescence, and germination of seed. Quantitative PCR analysis found that NAC members showing differential expression in different tissues. The study is useful for the study of D. candidum NAC family and the regulation mechanism in germination of seed embryo.