期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13911-13916
DOI：10.1073/pnas.1613394113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceFlower size can change rapidly in evolution; in particular, the frequent transition from animal-mediated out-crossing to self-pollination is often associated with a dramatic, yet rapid and specific, reduction in flower size. Here we demonstrate that the small petals of the selfing red Shepherds Purse (Capsella rubella) are because of a specific reduction in the activity of a general growth factor in petals. Different-strength versions of this growth gene were already present in the ancestral out-breeding population, and capture of a weak version from this pool can explain the rapid reduction of petal size in C. rubella. The additive effects of segregating small-effect mutations with low pleiotropy allowed specific modulation of petal size to enable adaptation to a new mode of reproduction. Mating system shifts recurrently drive specific changes in organ dimensions. The shift in mating system from out-breeding to selfing is one of the most frequent evolutionary transitions in flowering plants and is often associated with an organ-specific reduction in flower size. However, the evolutionary paths along which polygenic traits, such as size, evolve are poorly understood. In particular, it is unclear how natural selection can specifically modulate the size of one organ despite the pleiotropic action of most known growth regulators. Here, we demonstrate that allelic variation in the intron of a general growth regulator contributed to the specific reduction of petal size after the transition to selfing in the genus Capsella. Variation within this intron affects an organ-specific enhancer that regulates the level of STERILE APETALA (SAP) protein in the developing petals. The resulting decrease in SAP activity leads to a shortening of the cell proliferation period and reduced number of petal cells. The absence of private polymorphisms at the causal region in the selfing species suggests that the small-petal allele was captured from standing genetic variation in the ancestral out-crossing population. Petal-size variation in the current out-crossing population indicates that several small-effect mutations have contributed to reduce petal-size. These data demonstrate how tissue-specific regulatory elements in pleiotropic genes contribute to organ-specific evolution. In addition, they provide a plausible evolutionary explanation for the rapid evolution of flower size after the out-breeding-to-selfing transition based on additive effects of segregating alleles.
关键词：morphological evolution ; growth control ; standing variation ; organ-specific evolution ; intronic cis -regulatory element
