Dobritsa Anna A, Shrestha Jay, Morant Marc, Pinot Franck, Matsuno Michiyo, Swanson Robert, Møller Birger Lindberg, Preuss Daphne
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637, USA.
Plant Physiol. 2009 Oct;151(2):574-89. doi: 10.1104/pp.109.144469. Epub 2009 Aug 21.
Sporopollenin is the major component of the outer pollen wall (exine). Fatty acid derivatives and phenolics are thought to be its monomeric building blocks, but the precise structure, biosynthetic route, and genetics of sporopollenin are poorly understood. Based on a phenotypic mutant screen in Arabidopsis (Arabidopsis thaliana), we identified a cytochrome P450, designated CYP704B1, as being essential for exine development. CYP704B1 is expressed in the developing anthers. Mutations in CYP704B1 result in impaired pollen walls that lack a normal exine layer and exhibit a characteristic striped surface, termed zebra phenotype. Heterologous expression of CYP704B1 in yeast cells demonstrated that it catalyzes omega-hydroxylation of long-chain fatty acids, implicating these molecules in sporopollenin synthesis. Recently, an anther-specific cytochrome P450, denoted CYP703A2, that catalyzes in-chain hydroxylation of lauric acid was also shown to be involved in sporopollenin synthesis. This shows that different classes of hydroxylated fatty acids serve as essential compounds for sporopollenin formation. The genetic relationships between CYP704B1, CYP703A2, and another exine gene, MALE STERILITY2, which encodes a fatty acyl reductase, were explored. Mutations in all three genes resulted in pollen with remarkably similar zebra phenotypes, distinct from those of other known exine mutants. The double and triple mutant combinations did not result in the appearance of novel phenotypes or enhancement of single mutant phenotypes. This implies that each of the three genes is required to provide an indispensable subset of fatty acid-derived components within the sporopollenin biosynthesis framework.
孢粉素是花粉外壁（外壁）的主要成分。脂肪酸衍生物和酚类物质被认为是其单体结构单元，但孢粉素的精确结构、生物合成途径和遗传学仍知之甚少。基于对拟南芥的表型突变体筛选，我们鉴定出一种细胞色素P450，命名为CYP704B1，它对花粉外壁发育至关重要。CYP704B1在发育中的花药中表达。CYP704B1的突变导致花粉壁受损，缺乏正常的外壁层，并呈现出特征性的条纹表面，称为斑马表型。CYP704B1在酵母细胞中的异源表达表明它催化长链脂肪酸的ω-羟基化，这意味着这些分子参与孢粉素的合成。最近，一种花药特异性细胞色素P450，命名为CYP703A2，它催化月桂酸的链内羟基化，也被证明参与孢粉素的合成。这表明不同类别的羟基化脂肪酸是孢粉素形成的必需化合物。我们探究了CYP704B1、CYP703A2和另一个花粉外壁基因MALE STERILITY2之间的遗传关系，MALE STERILITY2编码一种脂肪酰还原酶。这三个基因的突变都导致花粉呈现出非常相似的斑马表型，与其他已知的花粉外壁突变体不同。双突变和三突变组合并没有导致新表型的出现或单突变体表型的增强。这意味着这三个基因中的每一个都需要提供孢粉素生物合成框架内脂肪酸衍生成分中不可或缺的子集。
