de Azevedo Souza Clarice, Kim Sung Soo, Koch Stefanie, Kienow Lucie, Schneider Katja, McKim Sarah M, Haughn George W, Kombrink Erich, Douglas Carl J
Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Plant Cell. 2009 Feb;21(2):507-25. doi: 10.1105/tpc.108.062513. Epub 2009 Feb 13.
Acyl-CoA Synthetase (ACOS) genes are related to 4-coumarate:CoA ligase (4CL) but have distinct functions. The Arabidopsis thaliana ACOS5 protein is in clade A of Arabidopsis ACOS proteins, the clade most closely related to 4CL proteins. This clade contains putative nonperoxisomal ACOS enzymes conserved in several angiosperm lineages and in the moss Physcomitrella patens. Although its function is unknown, ACOS5 is preferentially expressed in the flowers of all angiosperms examined. Here, we show that an acos5 mutant produced no pollen in mature anthers and no seeds by self-fertilization and was severely compromised in pollen wall formation apparently lacking sporopollenin or exine. The phenotype was first evident at stage 8 of anther development and correlated with maximum ACOS5 mRNA accumulation in tapetal cells at stages 7 to 8. Green fluorescent protein-ACOS5 fusions showed that ACOS5 is located in the cytoplasm. Recombinant ACOS5 enzyme was active against oleic acid, allowing kinetic constants for ACOS5 substrates to be established. Substrate competition assays indicated broad in vitro preference of the enzyme for medium-chain fatty acids. We propose that ACOS5 encodes an enzyme that participates in a conserved and ancient biochemical pathway required for sporopollenin monomer biosynthesis that may also include the Arabidopsis CYP703A2 and MS2 enzymes.
酰基辅酶A合成酶（ACOS）基因与4-香豆酸：辅酶A连接酶（4CL）相关，但具有不同的功能。拟南芥ACOS5蛋白属于拟南芥ACOS蛋白的A类，该类与4CL蛋白关系最为密切。该类包含在几个被子植物谱系和苔藓小立碗藓中保守的推定非过氧化物酶体ACOS酶。尽管其功能尚不清楚，但ACOS5在所有检测的被子植物的花中优先表达。在这里，我们表明acos5突变体在成熟花药中不产生花粉，自花授粉不产生种子，并且在花粉壁形成方面严重受损，显然缺乏孢粉素或外壁。该表型在花药发育的第8阶段首次明显，并且与第7至8阶段绒毡层细胞中ACOS5 mRNA的最大积累相关。绿色荧光蛋白-ACOS5融合蛋白表明ACOS5位于细胞质中。重组ACOS5酶对油酸有活性，从而可以确定ACOS5底物的动力学常数。底物竞争试验表明该酶在体外对中链脂肪酸具有广泛的偏好。我们提出ACOS5编码一种酶，该酶参与孢粉素单体生物合成所需的保守且古老的生化途径，该途径可能还包括拟南芥CYP703A2和MS2酶。
