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：2012
卷号：109
期号：46
页码：18873-18878
DOI：10.1073/pnas.1213498109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Ribulose-1,5-Biphosphate-carboxylase-oxygenase (RuBisCO) has a crucial role in carbon fixation but a slow catalytic rate, a problem overcome in some plant lineages by physiological and anatomical traits that elevate carbon concentrations around the enzyme. Such carbon-concentrating mechanisms are hypothesized to have evolved during periods of low atmospheric CO2. Hornworts, the sister to vascular plants, have a carbon-concentrating mechanism that relies on pyrenoids, proteinaceous bodies mostly consisting of RuBisCO. We generated a phylogeny based on mitochondrial and plastid sequences for 36% of the approximately 200 hornwort species to infer the history of gains and losses of pyrenoids in this clade; we also used fossils and multiple dating approaches to generate a chronogram for the hornworts. The results imply five to six origins and an equal number of subsequent losses of pyrenoids in hornworts, with the oldest pyrenoid gained ca. 100 Mya, and most others at <35 Mya. The nonsynchronous appearance of pyrenoid-containing clades, the successful diversification of pyrenoid-lacking clades during periods with low [CO2], and the maintenance of pyrenoids during episodes of high [CO2] all argue against the previously proposed relationship between pyrenoid origin and low [CO2]. The selective advantages, and costs, of hornwort pyrenoids thus must relate to additional factors besides atmospheric CO2.
