Gene Discovery Research Group, RIKEN Plant Science Center, 1-7-22 Suehiro, Tsurumi, Yokohama 230-0045, Japan.
J Plant Physiol. 2011 Nov 1;168(16):2001-5. doi: 10.1016/j.jplph.2011.05.014. Epub 2011 Jun 21.
In plants, pollen is the male gametophyte that is generated from microspores, which are haploid cells produced after meiosis of diploid pollen mother cells in floral anthers. In normal maturation, microspores interact with the tapetum, which consists of one layer of metabolically active cells enclosing the locule in anthers. The tapetum plays several important roles in the maturation of microspores. ATP-binding cassette (ABC) transporters are a highly conserved protein super-family that uses the energy released in ATP hydrolysis to transport substrates. The ABC transporter gene family is more diverse in plants than in animals. Previously, we reported that an Arabidopsis half-size type ABC transporter gene, COF1/AtWBC11/AtABCG11, is involved in lipid transport for the construction of cuticle layers and pollen coats in normal organ formation, as compared to CER5/AtWBC12/AtABCG12. However, physiological functions of most other ABCG members are unknown. Here, we identified another family gene, AtABCG26, which is required for pollen development in Arabidopsis. An AtABCG26 mutant developed very few pollen grains, resulting in a male-sterile phenotype. By investigating microspore and pollen development in this mutant, we observed that there was a slight abnormality in tetrad morphology prior to the formation of haploid microspores. At a later stage, we could not detect exine deposition on the microspore surface. During pollen maturation, many grains in the mutant anthers got aborted, and surviving grains were found to be defective in mitosis. Transmission of the mutant allele through male gametophytes appeared to be normal in genetic transmission analysis, supporting the view that the pollen function was disturbed by sporophytic defects in the AtABCG26 mutant. AtABCG26 can be expected to be involved in the transport of substrates such as sporopollenin monomers from tapetum to microspores, which both are plant-specific structures critical to pollen development.
在植物中，花粉是由小孢子产生的雄性配子体，小孢子是二倍体花粉母细胞减数分裂后产生的单倍体细胞。在正常成熟过程中，小孢子与绒毡层相互作用，绒毡层由一层代谢活跃的细胞组成，包围着花药中的腔室。绒毡层在小孢子的成熟过程中发挥着几个重要的作用。ATP 结合盒（ABC）转运蛋白是一个高度保守的蛋白质超家族，它利用 ATP 水解释放的能量来运输底物。ABC 转运蛋白基因家族在植物中的多样性比在动物中更高。以前，我们报道过拟南芥半尺寸类型 ABC 转运蛋白基因 COF1/AtWBC11/AtABCG11 参与脂质运输，用于构建正常器官形成中的角质层和花粉外壁，而 CER5/AtWBC12/AtABCG12 则不参与。然而，大多数其他 ABCG 成员的生理功能尚不清楚。在这里，我们鉴定了另一个家族基因 AtABCG26，它是拟南芥花粉发育所必需的。AtABCG26 突变体产生的花粉粒很少，导致雄性不育表型。通过研究该突变体中小孢子和花粉的发育，我们观察到在形成单倍体小孢子之前，四分体形态有轻微异常。在后期，我们无法检测到小孢子表面的外壁沉积。在花粉成熟过程中，突变体花药中的许多花粉粒都夭折了，存活的花粉粒在有丝分裂中发现有缺陷。通过雄性配子体传递突变等位基因在遗传传递分析中似乎是正常的，这支持了这样一种观点，即在 AtABCG26 突变体中，花粉功能是由孢子体缺陷干扰的。AtABCG26 可能参与了从绒毡层向小孢子运输底物的过程，如外壁的单体，这两种结构都是花粉发育所必需的植物特异性结构。
