Bitter acids, known for their use as beer flavoring and for their diverse biological activities, are predominantly formed in hop （Humulus lupulus） glandular trichomes. Branched short-chain acyI-CoAs （e.g. isobutyry...Bitter acids, known for their use as beer flavoring and for their diverse biological activities, are predominantly formed in hop （Humulus lupulus） glandular trichomes. Branched short-chain acyI-CoAs （e.g. isobutyryI-CoA, isovaleryl- CoA and 2-methylbutyryI-CoA）, derived from the degradation of branched-chain amino acids （BCAAs）, are essential building blocks for the biosynthesis of bitter acids in hops. However, little is known regarding what components are needed to produce and maintain the pool of branched short-chain acyI-CoAs in hop trichomes. Here, we present several lines of evidence that both CoA ligases and thioesterases are likely involved in bitter acid biosynthesis. Recombinant HICCL2 （carboxyl CoA ligase） protein had high specific activity for isovaleric acid as a substrate （Kcat/Km = 4100 s-~ M-l）, whereas recombinant HICCL4 specifically utilized isobutyric acid （Kcat/Km = 1800 s-1 M-1） and 2-methylbutyric acid （Kcat/ Km = 6900 s-1 M-~） as substrates. Both HICCLs, like hop valerophenone synthase （HIVPS）, were expressed strongly in glandular trichomes and localized to the cytoplasm. Co-expression of HICCL2 and HICCL4 with HIVPS in yeast led to significant production of acylphloroglucinols （the direct precursors for bitter acid biosynthesis）, which further confirmed the biochemical function of these two HICCLs in vivo. Functional identification of a thioesterase that catalyzed the reverse reaction of CCLs in mitochondria, together with the comprehensive analysis of genes involved BCAA catabolism, supported the idea that cytosolic CoA ligases are required for linking BCAA degradation and bitter acid biosynthesis in glandular trichomes. The evolution and other possible physiological roles of branched short-chain fatty acid：CoA ligases in planta are also discussed.展开更多
Artemisinin, the key ingredient of first-line antimalarial drugs, has large demand every year. The native plant, which produces small quantities of artemisinin, remains as its main source and thus results in a short s...Artemisinin, the key ingredient of first-line antimalarial drugs, has large demand every year. The native plant, which produces small quantities of artemisinin, remains as its main source and thus results in a short supply of artemisinin. Intensified efforts have been carried out to elevate artemisinin production. However, the routine metabolic engineering strategy, via overexpressing or down-regulating genes in artemisinin biosynthesis branch pathways, was not very effective as desired. Glandular secretory trichomes, sites of artemisinin biosynthesis on the surface of Artemisia annua L.(A. annua), are the new target for increasing artemisinin yield. In general, the population and morphology of glandular secretory trichomes in A. annua(Aa GSTs) are often positively correlated with artemisinin content. Improved understanding of Aa GSTs will shed light on the opportunities for increasing plant-derived artemisinin. This review article will refresh classification of trichomes in A. annua and provide an overview of the recent achievements regarding Aa GSTs and artemisinin. To have a full understanding of Aa GSTs,factors that are associated with trichome morphology and density will have to be further investigated, such as genes,micro RNAs and phytohormones. The purpose of thisreview was to(1) update the knowledge of the relation between Aa GSTs and artemisinin, and(2) propose new avenues to increase artemisinin yield by harnessing the potential biofactories, Aa GSTs.展开更多
基金the National Program on Key Basic Research Projects，the 'One hundred talents' project of the Chinese Academy of Sciences，the National Natural Sciences Foundation of China，the National Science Foundation，the State Key Laboratory of Plant Genomics of China
文摘Bitter acids, known for their use as beer flavoring and for their diverse biological activities, are predominantly formed in hop （Humulus lupulus） glandular trichomes. Branched short-chain acyI-CoAs （e.g. isobutyryI-CoA, isovaleryl- CoA and 2-methylbutyryI-CoA）, derived from the degradation of branched-chain amino acids （BCAAs）, are essential building blocks for the biosynthesis of bitter acids in hops. However, little is known regarding what components are needed to produce and maintain the pool of branched short-chain acyI-CoAs in hop trichomes. Here, we present several lines of evidence that both CoA ligases and thioesterases are likely involved in bitter acid biosynthesis. Recombinant HICCL2 （carboxyl CoA ligase） protein had high specific activity for isovaleric acid as a substrate （Kcat/Km = 4100 s-~ M-l）, whereas recombinant HICCL4 specifically utilized isobutyric acid （Kcat/Km = 1800 s-1 M-1） and 2-methylbutyric acid （Kcat/ Km = 6900 s-1 M-~） as substrates. Both HICCLs, like hop valerophenone synthase （HIVPS）, were expressed strongly in glandular trichomes and localized to the cytoplasm. Co-expression of HICCL2 and HICCL4 with HIVPS in yeast led to significant production of acylphloroglucinols （the direct precursors for bitter acid biosynthesis）, which further confirmed the biochemical function of these two HICCLs in vivo. Functional identification of a thioesterase that catalyzed the reverse reaction of CCLs in mitochondria, together with the comprehensive analysis of genes involved BCAA catabolism, supported the idea that cytosolic CoA ligases are required for linking BCAA degradation and bitter acid biosynthesis in glandular trichomes. The evolution and other possible physiological roles of branched short-chain fatty acid：CoA ligases in planta are also discussed.
基金supported by the National Natural Science Foundation of China (Grant Nos. 31300159 U1405215)+2 种基金‘‘Pujiang Talent’’ program (13PJ1411000) Shanghai Science and Technology Development Funds (14QB1402700)Program 15391900500 from Science and Technology Commission of Shanghai Municipality and Technology Committee and Seedling Cultivation Fund of Outstanding Master, Second Military Medical University
文摘Artemisinin, the key ingredient of first-line antimalarial drugs, has large demand every year. The native plant, which produces small quantities of artemisinin, remains as its main source and thus results in a short supply of artemisinin. Intensified efforts have been carried out to elevate artemisinin production. However, the routine metabolic engineering strategy, via overexpressing or down-regulating genes in artemisinin biosynthesis branch pathways, was not very effective as desired. Glandular secretory trichomes, sites of artemisinin biosynthesis on the surface of Artemisia annua L.(A. annua), are the new target for increasing artemisinin yield. In general, the population and morphology of glandular secretory trichomes in A. annua(Aa GSTs) are often positively correlated with artemisinin content. Improved understanding of Aa GSTs will shed light on the opportunities for increasing plant-derived artemisinin. This review article will refresh classification of trichomes in A. annua and provide an overview of the recent achievements regarding Aa GSTs and artemisinin. To have a full understanding of Aa GSTs,factors that are associated with trichome morphology and density will have to be further investigated, such as genes,micro RNAs and phytohormones. The purpose of thisreview was to(1) update the knowledge of the relation between Aa GSTs and artemisinin, and(2) propose new avenues to increase artemisinin yield by harnessing the potential biofactories, Aa GSTs.
