Evolution and biogeography of gymnosperms

Living gymnosperms comprise only a little more than 1000 species, but represent four of the five main lineages of seed plants, including cycads, ginkgos, gnetophytes and conifers. This group has huge ecological and economic value, and has drawn great interest from the scientific community. Here we review recent advances in our understanding of gymnosperm evolution and biogeography, including phylogenetic relationships at different taxonomic levels, patterns of species diversification, roles of vicariance and dispersal in development of intercontinental disjunctions, modes of molecular evolution in different genomes and lineages, and mechanisms underlying the formation of large nuclear genomes. It is particularly interesting that increasing evidence supports a sister relationship between Gnetales and Pinaceae (the Gnepine hypothesis) and the contribution of recent radiations to present species diversity, and that expansion of retrotransposons is responsible for the large and complex nuclear genome of gymnosperms. In addition, multiple coniferous genera such as Picea very likely originated in North America and migrated into the Old World, further indicating that the center of diversity is not necessarily the place of origin. The Bering Land Bridge acted as an important pathway for dispersal of gymnosperms in the Northern Hemisphere. Moreover, the genome sequences of conifers provide an unprecedented opportunity and an important platform for the evolutionary studies of gymnosperms, and will also shed new light on evolution of many important gene families and biological pathways in seed plants. (c) 2014 Elsevier Inc. All rights reserved.

现存的裸子植物仅包含1000多种，但代表了种子植物五个主要谱系中的四个，包括苏铁、银杏、买麻藤类和针叶树。这个类群具有巨大的生态和经济价值，引起了科学界的极大兴趣。在此，我们综述了在裸子植物进化和生物地理学理解方面的最新进展，包括不同分类水平上的系统发育关系、物种多样化模式、隔离和扩散在洲际间断分布形成中的作用、不同基因组和谱系中分子进化的模式以及大核基因组形成的潜在机制。特别有趣的是，越来越多的证据支持买麻藤目和松科之间的姐妹群关系（买麻藤 - 松假说）以及近期的辐射演化对现存物种多样性的贡献，并且反转录转座子的扩张是裸子植物大而复杂的核基因组的原因。此外，多个针叶树属，如云杉属很可能起源于北美洲，然后迁移到旧大陆，这进一步表明多样性中心不一定是起源地。白令陆桥是裸子植物在北半球扩散的重要通道。而且，针叶树的基因组序列为裸子植物的进化研究提供了前所未有的机遇和重要平台，也将为种子植物中许多重要基因家族和生物途径的进化提供新的线索。（c）2014爱思唯尔公司。保留所有权利。