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Int J Mol Sci. 2019 Sep 11;20(18). pii: E4499. doi: 10.3390/ijms20184499.

Molecular Cloning and Functional Identification of a Squalene Synthase Encoding Gene from Alfalfa (Medicago sativa L.).

Author information

1
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. kangjunmei@caas.cn.
2
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. zhqynancy@126.com.
3
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. jiangxu2009@yeah.net.
4
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. tiejunzhang@126.com.
5
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. dragongodsgod@163.com.
6
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. qchyang66@163.com.
7
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China. wangzhen@caas.cn.

Abstract

The quality of alfalfa, a main forage legume worldwide, is of great importance for the dairy industry and is affected by the content of triterpene saponins. These natural terpenoid products of triterpene aglycones are catalyzed by squalene synthase (SQS), a highly conserved enzyme present in eukaryotes. However, there is scare information on alfalfa SQS. Here, an open reading frame (ORF) of SQS was cloned from alfalfa. Sequence analysis showed MsSQS had the same exon/intron composition and shared high homology with its orthologs. Bioinformatic analysis revealed the deduced MsSQS had two transmembrane domains. When transiently expressed, GFP-MsSQS fusion protein was localized on the plasma membrane of onion epidermal cells. Removal of the C-terminal transmembrane domain of MsSQS improved solubility in Escherichia coli. MsSQS was preferably expressed in roots, followed by leaves and stems. MeJA treatment induced MsSQS expression and increased the content of total saponins. Overexpression of MsSQS in alfalfa led to the accumulation of total saponins, suggesting a correlation between MsSQS expression level with saponins content. Therefore, MsSQS is a canonical squalene synthase and contributes to saponin synthesis in alfalfa. This study provides a key candidate gene for genetic manipulation of the synthesis of triterpene saponins, which impact both plant and animal health.

KEYWORDS:

alfalfa; saponins; squalene synthase; transgenic alfalfa

PMID:
31514406
DOI:
10.3390/ijms20184499
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