LAUSR

Achyranthes bidentata, a traditional perennial medicine herb in China, contains a rich source of important pharmaceutically active phytoecdysteroids including 20-hydroxyecdysone (20E). The growth of A. bidentata plants and 20E production are suppressed under abiotic stress condition. Expansins are plant cell wall-loosening proteins to play important roles in different environment stresses. In this study, we tried to clone an expansin gene (designed as AbEXP) from A. bidentata and characterize its transcriptional response to abiotic stresses (salt stress and nutrient deficiency). The cDNA of AbEXP contained 1584 nucleotides with a complete opening reading frame of 786 nucleotides to encode a peptide of 261 amino acids. The expression of the gene was detected in stems, roots or leaves, and was relatively abundant in stems. The expression levels of AbEXP under the salinity stress (25 mM NaCl) were increased 51.7-folds in roots but decreased in stems significantly. P and K deficiency enhanced the expression of AbEXP in roots and stems, but down-regulated the levels in leaves compared with control conditions. Under N deficiency AbEXP expression levels in roots and leaves were down-regulated by 9.95-fold and 4.58-fold, respectively. The expression level in roots was 43.9-fold of the control level under Fe deficiency while no significant changes of the expression were detected in stems and leaves. Although the growth of A. bidentata seedlings was inhibited under both the salinity stress and nutrient deficiency, 20E content in roots was enhanced significantly under N and P deficiency. These results demonstrate that AbEXP could be involved in the responses to abiotic stresses and manipulation of the gene expression of AbEXP could promote growth and 20E production of A. bidentata.