The Huperzia selago Shoot Tip Transcriptome Sheds New Light on the Evolution of Leaves

Abstract

Lycopodiophyta—consisting of three orders, Lycopodiales, Isoetales and Selaginellales, with different types of shoot apical meristems (SAMs)—form the earliest branch among the extant vascular plants. They represent a sister group to all other vascular plants, from which they differ in that their leaves are microphylls—that is, leaves with a single, unbranched vein, emerging from the protostele without a leaf gap—not megaphylls. All leaves represent determinate organs originating on the flanks of indeterminate SAMs. Thus, leaf formation requires the suppression of indeterminacy, that is, of KNOX transcription factors. In seed plants, this is mediated by different groups of transcription factors including ARP and YABBY.We generated a shoot tip transcriptome of Huperzia selago (Lycopodiales) to examine the genes involved in leaf formation. Our H. selago transcriptome does not contain any ARP homolog, although transcriptomes of Selaginella spp. do. Surprisingly, we discovered a YABBY homolog, although these transcription factors were assumed to have evolved only in seed plants.The existence of a YABBY homolog in H. selago suggests that YABBY evolved already in the common ancestor of the vascular plants, and subsequently was lost in some lineages like Selaginellales, whereas ARP may have been lost in Lycopodiales. The presence of YABBY in the common ancestor of vascular plants would also support the hypothesis that this common ancestor had a simplex SAM. Furthermore, a comparison of the expression patterns of ARP in shoot tips of Selaginella kraussiana (Harrison CJ, etal. 2005. Independent recruitment of a conserved developmental mechanism during leaf evolution. Nature 434(7032):509–514.) and YABBY in shoot tips of H. selago implies that the development of microphylls, unlike megaphylls, does not seem to depend on the combined activities of ARP and YABBY. Altogether, our data show that Lycopodiophyta are a diverse group; so, in order to understand the role of Lycopodiophyta in evolution, representatives of Lycopodiales, Selaginellales, as well as of Isoetales, have to be examined.

Progress Towards Plant Community Transcriptomics: Pilot RNA-Seq Data from 24 Species of Vascular Plants at Harvard Forest

“…The assemblies are also reasonably complete with more than 70% of BUSCO genes present on average. This is a similar distribution of BUSCO scores to those in the recently published 1KP project One Thousand Plant Transcriptomes Initiative, 2019) and other studies (Blande et al, 2017;Evkaikina et al, 2017;Pokorn et al, 2017;Weisberg et al, 2017) . Like many transcriptome assemblies (Johnson et al, 2012;Carpenter et al, 2019;Patterson et al, 2019) , these assemblies also contain a large number of small scaffolds (<300 bp).…”

Fern genomes elucidate land plant evolution and cyanobacterial symbioses

“…YABBY, an important transcription factor that patterns leaf polarity in flowering plants, is absent in our fern genomes and in the genome of the lycophyte Selaginella moellendorffii 15 (Supplementary Table 8). Interestingly, a YABBY homologue was recently identified in a separate lycophyte species— Huperzia selago 16 —suggesting that YABBY has been lost at least twice in land plant evolution (in Selaginella and in ferns). How the differential retention of YABBY shaped the evolution of the vascular plant body plan requires further studies.…”

Simple and Divided Leaves in Ferns: Exploring the Genetic Basis for Leaf Morphology Differences in the Genus Elaphoglossum (Dryopteridaceae)

“…To gain a more detailed evolutionary history of Class I KNOX in ferns and to discover the putative Elaphoglossum Class I KNOX gene copies for our expression studies, we obtained representative species across the fern and lycophyte phylogeny from publicly available databases and by cloning. We included Class I KNOX genes previously published from the lycophytes Selaginella krausiana [ 10 ], Huperzia selago and Isoetes tegetiformans [ 87 ], and Lycopodium deuterodensum [ 88 ]; from the ferns Ceratopteris richardii [ 32 ], Elaphoglossum peltatum f. peltatum [ 33 ], and Equisetum diffusum [ 88 ]. We got these sequences from GenBank, the 1KP plant transcriptome project ( , accessed May 2018) databases, or directly from the published papers.…”