三叶木通转录组分析及三萜皂苷生物合成途径关键酶基因的发掘

为了解三叶木通(Akebia trifoliata(Thunb.)Koidz.)的三萜皂苷合成途径及其关键酶,本研究对其花、叶、根、茎进行转录组测序,组装获得了57.25 Gb数据,含140 859个unigenes,序列平均长度为1350 bp。KEGG代谢通路富集结果显示,517个unigenes参与三萜皂苷合成相关的3条代谢途径,其中415个unigenes编码三萜皂苷生物合成途径的19个关键酶。对三萜皂苷生物合成过程中的关键酶角鲨烯环氧酶(SE)进行序列分析和同源建模,发现其具有保守的底物结合结构域。将三叶木通茎与花、叶、根的基因表达水平进行比较,发现茎与根相比较其上调基因数目最多,其中295个差异表达基因(DEGs)与三萜皂苷生物合成途径相关。     

Methyl Farnesoate Plays a Dual Role in Regulating Drosophila Metamorphosis

Corpus allatum (CA) ablation results in juvenile hormone (JH) deficiency and pupal lethality in Drosophila. The fly CA produces and releases three sesquiterpenoid hormones: JH III bisepoxide (JHB3), JH III, and methyl farnesoate (MF). In the whole body extracts, MF is the most abundant sesquiterpenoid, followed by JHB3 and JH III. Knockout of JH acid methyl transferase (jhamt) did not result in lethality; it decreased biosynthesis of JHB3, but MF biosynthesis was not affected. RNAi-mediated reduction of 3-hydroxy-3-methylglutaryl CoA reductase (hmgcr) expression in the CA decreased biosynthesis and titers of the three sesquiterpenoids, resulting in partial lethality. Reducing hmgcr expression in the CA of the jhamt mutant further decreased MF titer to a very low level, and caused complete lethality. JH III, JHB3, and MF function through Met and Gce, the two JH receptors, and induce expression of Kr-h1, a JH primary-response gene. As well, a portion of MF is converted to JHB3 in the hemolymph or peripheral tissues. Topical application of JHB3, JH III, or MF precluded lethality in JH-deficient animals, but not in the Met gce double mutant. Taken together, these experiments show that MF is produced by the larval CA and released into the hemolymph, from where it exerts its anti-metamorphic effects indirectly after conversion to JHB3, as well as acting as a hormone itself through the two JH receptors, Met and Gce.