Steroidal saponin profiles and their key genes for synthesis and regulation in Asparagus officinalis L. by joint analysis of metabolomics and transcriptomics.

BACKGROUND: Asparagus officinalis L. is a worldwide cultivated vegetable enrichened in both nutrient and steroidal saponins with multiple pharmacological activities. The upstream biosynthetic pathway of steroidal saponins (USSP) for cholesterol (CHOL) synthesis has been studied, while the downstream pathway of steroidal saponins (DSSP) starting from cholesterol and its regulation in asparagus remains unknown. RESULTS: Metabolomics, Illumina RNAseq, and PacBio IsoSeq strategies were applied to different organs of both cultivated green and purple asparagus to detect the steroidal metabolite profiles & contents and to screen their key genes for biosynthesis and regulation. The results showed that there is a total of 427 compounds, among which 18 steroids were detected with fluctuated concentrations in roots, spears and flowering twigs of two garden asparagus cultivars. The key genes of DSSP include; steroid-16-hydroxylase (S16H), steroid-22-hydroxylase (S22H) and steroid-22-oxidase-16-hydroxylase (S22O-16H), steroid-26-hydroxylase (S26H), steroid-3-ß-glycosyltransferase (S3ßGT) and furostanol glycoside 26-O-beta-glucosidases (F26GHs) which were correlated with the contents of major steroidal saponins were screened, and the transcriptional factors (TFs) co-expressing with the resulted from synthetic key genes, including zinc fingers (ZFs), MYBs and WRKYs family genes were also screened. CONCLUSIONS: Based on the detected steroidal chemical structures, profiles and contents which correlated to the expressions of screened synthetic and TFs genes, the full steroidal saponin synthetic pathway (SSP) of asparagus, including its key regulation networks was proposed for the first time.

Profiles of phenolics and their synthetic pathways in Asparagus officinalis L.

The synthetic pathways of some phenolics compounds in asparagus have been reported, however, the diversified phenolics compounds including their modification and transcription regulation remains unknown. Thus, multi-omics strategies were applied to detect the phenolics profiles, contents, and screen the key genes for phenolics biosynthesis and regulation in asparagus. A total of 437 compounds, among which 204 phenolics including 105 flavonoids and 82 phenolic acids were detected with fluctuated concentrations in roots (Rs), spears (Ss) and flowering twigs (Fs) of the both green and purple cultivars. Based on the detected phenolics profiles and contents correlated to the gene expressions of screened synthetic enzymes and regulatory TFs, a full phenolics synthetic pathway of asparagus was proposed for the first time, essential for future breeding of asparagus and scaled healthy phenolics production using synthetic biological strategies.

AoSAP8-P encoding A20 and/or AN1 type zinc finger protein in asparagus officinalis L. Improving stress tolerance in transgenic Nicotiana sylvestris.

The full length CDS of an A20 and AN1 type zinc finger gene (named AoSAP8-P), located nearby the male specific Y chromosome (MSY) region of Asparagus officinalis (garden asparagus) was amplified by RT-PCR from purple passion. This gene, predicted as the stress associated protein (SAPs) gene families, encodes 172 amino acids with multiple cis elements including light, stress response box, MYB and ERF binding sites on its promoter. To analyze its function, the gene expression of different organs in different asparagus gender were analyzed and the overexpressed transgenic Nicotiana sylvestris lines were generated. The results showed the gene was highly expressed in both flower and root of male garden asparagus; the germination rate of seeds of the T2 transgenic lines (T2-5-4 and T2-7-1) under the stress conditions of 125 mM NaCl and 150 mM mannitol were significantly higher than the wild type (WT) respectively. When the potted T2-5-4, T2-7-1 lines and WT were subjected to drought stress for 24 days and the leaf discs immerged into 20 % PEG6000 and 300 mM NaCl solution for 48 h respectively, the T2-5-4 and T2-7-1 with AoSAP8-P expression showed stronger drought, salt and osmotic stress tolerance. When compared, the effects of AoSAP8-P overexpression on productive development showed that the flowering time of transgenic lines, were âˆ¼ 9 day earlier with larger but fewer pollens than its WT counterparts. However, there were no significant differences in anthers, stigmas and pollen viability between the transgenic lines and WT. Our results suggested that, the AoSAP8-P gene plays a role in improving the stress resistance and shortening seeds generation time for perianal survival during the growth and development of garden asparagus.