A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots
A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots
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DOI：
10.1073/pnas.231324698
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发表时间：
2001-11-06
影响因子：
11.1
通讯作者：
Osbourn, A
中科院分区：
文献类型：
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作者：
Haralampidis, K;Bryan, G;Osbourn, A
许多植物合成抗菌次级代谢物作为其正常生长和发育程序的一部分，通常将它们隔离在组织中，在那里它们可以保护免受微生物的攻击。这些包括糖基化的三萜类化合物（皂苷），其是被人类开发用于各种目的（包括用作药物）的天然产物[Hostettmann，K. &马斯顿，A.（1995）Saponins（剑桥Univ.Press，剑桥，U.K.）]。关于植物中合成这一重要的次级代谢产物家族所需的基因知之甚少。在这里，我们展示了新的氧化角鲨烯环化酶AsbAS1催化的第一个关键步骤，在燕麦根中积累的抗真菌三萜皂苷的合成。我们还表明，两个叠氮化钠产生的皂苷缺乏突变体的燕麦，这定义的Sad 1遗传互补组，是有缺陷的基因编码这种酶，并提供分子遗传学证据表明AsbAS 1，三萜皂苷生物合成和抗病性之间的直接联系。AsbAS 1的直系同源基因在现代谷物中不存在，并且可能在选择过程中丢失，这提高了该基因可用于增强作物抗病性的可能性。
Many plants synthesize antimicrobial secondary metabolites as part of their normal program of growth and development, often sequestering them in tissues where they may protect against microbial attack. These include glycosylated triterpenoids (saponins), natural products that are exploited by man for a variety of purposes including use as drugs [Hostettmann, K. & Marston, A. (1995) Saponins (Cambridge Univ. Press, Cambridge, U.K.)]. Very little is known about the genes required for the synthesis of this important family of secondary metabolites in plants. Here we show the novel oxidosqualene cyclase AsbAS1 catalyzes the first committed step in the synthesis of antifungal triterpenoid saponins that accumulate in oat roots. We also demonstrate that two sodium azide-generated saponin-deficient mutants of oat, which define the Sad1 genetic complementation group, are defective in the gene encoding this enzyme and provide molecular genetic evidence indicating a direct link between AsbAS1, triterpenoid saponin biosynthesis, and disease resistance. Orthologs of AsbAS1 are absent from modern cereals and may have been lost during selection, raising the possibility that this gene could be exploited to enhance disease resistance in crop plants.