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Abstract Although the seed is a key morphological innovation, its origin remains unknown and molecular data outside angiosperms is still limited. Ginkgo biloba, with a unique place in plant evolution, being one of the first extant gymnosperms where seeds evolved, can testify to the evolution and development of the seed. Initially, to better understand the development of the ovules in Ginkgo biloba ovules, we performed spatio-temporal expression analyses in seeds at early developing stages, of six candidate gene homologues known in angiosperms: WUSCHEL, AINTEGUMENTA, BELL1, KANADI, UNICORN, and C3HDZip . Surprisingly, the expression patterns of most these ovule homologues indicate that they are not wholly conserved between angiosperms and Ginkgo biloba . Consistent with previous studies on early diverging seedless plant lineages, ferns, lycophytes, and bryophytes, many of these candidate genes are mainly expressed in mega- and micro-sporangia. Through in-depth comparative transcriptome analyses of Ginkgo biloba developing ovules, pollen cones, and megagametophytes we have been able to identify novel genes, likely involved in ovule development. Finally, our expression analyses support the synangial or neo-synangial hypotheses for the origin of the seed, where the sporangium developmental network was likely co-opted and restricted during integument evolution.
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The Cycas genome and the early evolution of seed plants
Abstract Cycads represent one of the most ancient lineages of living seed plants. Identifying genomic features uniquely shared by cycads and other extant seed plants, but not non-seed-producing plants, may shed light on the origin of key innovations, as well as the early diversification of seed plants. Here, we report the 10.5-Gb reference genome ofCycas panzhihuaensis, complemented by the transcriptomes of 339 cycad species. Nuclear and plastid phylogenomic analyses strongly suggest that cycads andGinkgoform a clade sister to all other living gymnosperms, in contrast to mitochondrial data, which place cycads alone in this position. We found evidence for an ancient whole-genome duplication in the common ancestor of extant gymnosperms. TheCycasgenome contains four homologues of thefitDgene family that were likely acquired via horizontal gene transfer from fungi, and these genes confer herbivore resistance in cycads. The male-specific region of the Y chromosome ofC. panzhihuaensiscontains a MADS-box transcription factor expressed exclusively in male cones that is similar to a system reported inGinkgo, suggesting that a sex determination mechanism controlled by MADS-box genes may have originated in the common ancestor of cycads andGinkgo. TheC. panzhihuaensisgenome provides an important new resource of broad utility for biologists.
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- Award ID(s):
- 1943371
- PAR ID:
- 10608349
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Nature
- Date Published:
- Journal Name:
- Nature Plants
- Volume:
- 8
- Issue:
- 4
- ISSN:
- 2055-0278
- Page Range / eLocation ID:
- 389 to 401
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41477-022-01129-7
