Understanding the molecular function of individual causal loci at the heterostyly supergene in Primula

点击翻译按钮获取中文摘要

Heterostyly is a fascinating adaptation to promote outbreeding and a classical paradigm of botany. In the most common type of heterostyly, plants either form flowers with long styles and short stamens, or short styles and long stamens. This reciprocal organ positioning reduces pollen wastage and promotes cross-pollination, thus increasing male fitness. In addition, in many heterostylous species selfing and the generation of unfit progeny due to inbreeding depression is limited by a self-incompatibility system, thus promoting female fitness. In primroses (Primula) the two floral forms are genetically determined by the S-locus as a complex supergene, i.e. a chromosomal region containing several individual genes that control the different traits, such as style or stamen length, and are held together by very tight linkage due to suppressed recombination. Over the last years, we have identified and begun to functionally characterize the individual causal loci at the S-locus supergene in Primula, with a particular focus on the female traits of style length and female self-incompatibility type regulated by CYP734A50, and on the control of anther position by GLO2. More recently, we have also obtained evidence that the hitherto poorly understood characters of pollen size and male self-incompatiblity are controlled by an interplay between the KFB-T and PUM-T genes. These studies lay the groundwork for a more detailed mechanistic understanding of how the encoded proteins fulfil their roles in modifying the suite of heterostyly traits between the morph and how they have gained these in the course of evolution. To address these issues, we will (1) determine the structural and molecular basis for the neofunctionalization of GLO2; (2) characterize in detail the role of KFB-T and PUM-T in regulating pollen size and male self-incompatibility type; and (3) use derived homostylous Primula genotypes to elucidate the molecular basis of the female self-incompatibility reaction. Together, these studies will provide unprecedented insight into a textbook problem in plant genetics and evolution and a model for supergene evolution and function in plants and animals.