van Der Hoeven R S, Monforte A J, Breeden D, Tanksley S D, Steffens J C
Departments of Plant Breeding and Plant Biology, Cornell University, Ithaca, New York 14850, USA.
Plant Cell. 2000 Nov;12(11):2283-94. doi: 10.1105/tpc.12.11.2283.
Segregation analysis between Lysopersicon esculentum (cultivated tomato) and L. hirsutum (wild form) in conjunction with positional verification by using near-isogenic lines demonstrated that biosynthesis of two structurally different classes of sesquiterpenes in these species is controlled by loci on two different chromosomes. A locus on chromosome 6, Sesquiterpene synthase1 (Sst1), was identified for which the L. esculentum allele is associated with the biosynthesis of beta-caryophyllene and alpha-humulene. At this same locus, the L. hirsutum allele is associated with biosynthesis of germacrene B, germacrene D, and an unidentified sesquiterpene. Genomic mapping, cDNA isolation, and heterologous expression of putative sesquiterpene synthases from both L. esculentum and L. hirsutum revealed that Sst1 is composed of two gene clusters 24 centimorgans apart, Sst1-A and Sst1-B, and that only the genes in the Sst1-A cluster are responsible for accumulation of chromosome 6-associated sesquiterpenes. At a second locus, Sst2, on chromosome 8, the L. hirsutum allele specified accumulation of alpha-santalene, alpha-bergamotene, and beta-bergamotene. Surprisingly, the L. esculentum allele for Sst2 is not associated with the expression of any sesquiterpenes, which suggests that cultivated tomato may have a nonfunctional allele. Sesquiterpene synthase cDNA clones on chromosome 6 do not cross-hybridize on genomic DNA gel blots with putative sesquiterpene synthases on chromosome 8, an indication that the genes in Sst1 and Sst2 are highly diverged, each being responsible for the biosynthesis of structurally different sets of sesquiterpenes.
对栽培番茄（番茄）和野生多毛番茄进行分离分析，并结合利用近等基因系进行的定位验证，结果表明，这两个物种中两类结构不同的倍半萜生物合成受两条不同染色体上的基因座控制。在6号染色体上鉴定出一个基因座，即倍半萜合酶1（Sst1），番茄的该等位基因与β-石竹烯和α-葎草烯的生物合成相关。在同一基因座上，多毛番茄的等位基因与杜松烯B、杜松烯D和一种未鉴定的倍半萜的生物合成相关。对番茄和多毛番茄推定的倍半萜合酶进行基因组定位、cDNA分离和异源表达分析，结果显示Sst1由两个相距24厘摩的基因簇Sst1-A和Sst1-B组成，且只有Sst1-A簇中的基因负责与6号染色体相关的倍半萜的积累。在8号染色体上的第二个基因座Sst2处，多毛番茄的等位基因决定了α-檀香烯、α-佛手柑烯和β-佛手柑烯的积累。令人惊讶的是，番茄中Sst2的等位基因与任何倍半萜的表达均无关联，这表明栽培番茄可能具有一个无功能的等位基因。6号染色体上的倍半萜合酶cDNA克隆在基因组DNA凝胶印迹上与8号染色体上推定的倍半萜合酶不发生交叉杂交，这表明Sst1和Sst2中的基因高度分化，各自负责结构不同的倍半萜组的生物合成。
