Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany.
Planta Med. 2010 Jun;76(9):928-34. doi: 10.1055/s-0030-1250036. Epub 2010 May 31.
Lignans in higher plants represent an ideal class of natural products to be investigated for the origin of stereochemical diversity since chiral lignans occur in pure enantiomeric form as well as in enantiomeric mixtures. Seeds of Linum usitatissimum contain 8S, 8'S-(+)- and 8R, 8'R-(-)-secoisolariciresinol [SS-(+)- and RR-(-)-secoisolariciresinol, respectively] as diglucosides (SS- and RR-secoisolariciresinol diglucosides) whereas aerial parts of flowering L. usitatissimum accumulate only lignans derived from RR-(-)-secoisolariciresinol. Pinoresinol-lariciresinol reductase (PLR) catalyzes two early steps in lignan biosynthesis. Up to now, only a cDNA encoding a PLR ( PLR-LU1) which is enantiospecific for the conversion of 8S, 8'S-(-)-pinoresinol (SS-pinoresinol) via 8S, 8'S-(-)-lariciresinol (SS-lariciresinol) to SS-(+)-secoisolariciresinol was cloned. Here we present the cloning of a cDNA encoding a RR-pinoresinol-RR-lariciresinol reductase ( PLR-LU2) from the leaves of L. usitatissimum which converts only RR-pinoresinol to RR-secoisolariciresinol. In leaves and stems of L. usitatissimum accumulating the 8R, 8'R-enantiomers of lignans, only PLR-LU2 was transcriptionally active. Both PLR-LU1 and PLR-LU2 transcripts were observed in seeds and contribute to the synthesis of SS- and RR-secoisolariciresinol, respectively. Thus, the enantiomeric composition of lignans in the organs of L. usitatissimum appears to be determined by the relative action of two PLRs with opposite enantiospecificities rather than by a single enzyme of low enantiospecificity.
高等植物中的木脂素是研究手性多样性起源的理想天然产物，因为手性木脂素以纯对映体形式以及对映体混合物形式存在。亚麻籽中含有 8S、8'S-(+)-和 8R、8'R-(-)-开环异落叶松脂素[分别为 SS-(+)-和 RR-(-)-开环异落叶松脂素]作为二葡萄糖苷（SS-和 RR-开环异落叶松脂素二葡萄糖苷），而开花期亚麻地上部分仅积累来源于 RR-(-)-开环异落叶松脂素的木脂素。松脂醇-橄榄脂素还原酶（PLR）催化木质素生物合成的两个早期步骤。到目前为止，只克隆了一个编码 PLR 的 cDNA（PLR-LU1），它对手性特异性转化 8S、8'S-(-)-松脂醇（SS-松脂醇）通过 8S、8'S-(-)-橄榄脂素（SS-橄榄脂素）转化为 SS-(+)-开环异落叶松脂素。在这里，我们介绍了从亚麻叶中克隆编码 RR-松脂醇-RR-橄榄脂素还原酶（PLR-LU2）的 cDNA，该酶仅将 RR-松脂醇转化为 RR-开环异落叶松脂素。在积累木脂素 8R、8'R-对映体的亚麻叶和茎中，只有 PLR-LU2 转录活跃。在种子中观察到 PLR-LU1 和 PLR-LU2 转录本，分别有助于 SS-和 RR-开环异落叶松脂素的合成。因此，亚麻器官中木质素的对映体组成似乎由两种具有相反手性特异性的 PLR 的相对作用决定，而不是由一种低手性特异性的单一酶决定。
