Analysis of saponin contents and expression of its synthetic genes upstream of cycloartenol in Asparagus officinalis
Steroidal saponins are active ingredients providing valuable pharmacological properties for health effects in the Asparagus officinalis vegetable. Therefore, elucidating its biosynthetic pathway and its regulation are of great significance to improve qualified asparagus production. With available sequencing data of asparagus, by blast analyzing of known genes associated phytosterol biosynthesis in model or well-studied medicinal plant, the asparagus steroidal saponin synthetic pathway is predicted to contain several steps to prepare C5 precursor IPP and DMAPP; cyclization and modifying of sterol skeleton and synthesis of steroidal glycoside conjugates. With the obtained pathway, the key intermediates, such as cycloarternol, diosgenin were predicted, and full length CDS of HMGS, FPPS, SS and partial CDS of SMT gene were cloned with amplification of RT-PCR. By using asparagus cultivar Jersey Knight, both green and white asparagus were produced in Mile county of Yunnan in China. With commercial spears and stalks with different age as materials, the contents of total saponins and diosgenin were determined, and simultaneously the expression profiles of HMGS, FPPS, SS and SMT gene were assayed. The results show that content of diosgenin in Green B (green asparagus collected by bald way) < white asparagus < Green S (green asparagus collected with stalks) < young stalk < mature stalk, as for contents of total saponin, the tendency of changes is same as diosgenin, except the content of total saponin in white asparagus is the lowest, and the four above cloned gene expressions show significant negative correlation with the content of total saponin in corresponding samples. The results indicate that the steps before cycloartenol forming and sterol C24 methylation step may not be key controlling points for both synthesis and accumulation of saponins in asparagus, and green asparagus collected with stalks will be the best cultivating method for both quantity and quality in asparagus production.
Hao, Kun, Lin, Chun, Xu, Peng, Wang, Yulong, Li, Xuemei and Mao, Zichao (2020). Analysis of saponin contents and expression of its synthetic genes upstream of cycloartenol in Asparagus officinalis. Acta Hortic. 1301, 207-218
asparagus, gene expression, saponin, biosynthesis