Acquisition and diversification of tendrilled leaves in Bignonieae (Bignoniaceae) involved changes in expression patterns of SHOOTMERISTEMLESS (STM), LEAFY/FLORICAULA (LFY/FLO), and PHANTASTICA (PHAN)

Shaping leaves through TALE homeodomain transcription factors

The first TALE homeodomain transcription factor gene to be described in plants was maize knotted1 (kn1). Dominant mutations in kn1 disrupt leaf development, with abnormal knots of tissue forming in the leaf blade. kn1 was found to be expressed in the shoot meristem but not in a peripheral region that gives rise to leaves. Furthermore, KN1 and closely related proteins were excluded from initiating and developing leaves. These findings were a prelude to a large body of work wherein TALE homeodomain proteins have been identified as vital regulators of meristem homeostasis and organ development in plants. KN1 homologues are widely represented across land plant taxa. Thus, studying the regulation and mechanistic action of this gene class has allowed investigations into the evolution of diverse plant morphologies. This review will focus on the function of TALE homeodomain transcription factors in leaf development in eudicots. Here, we discuss how TALE homeodomain proteins contribute to a spectrum of leaf forms, from the simple leaves of Arabidopsis thaliana to the compound leaves of Cardamine hirsuta and species beyond the Brassicaceae.

Tendril morphogenesis is regulated by a CsaTEN-CsaUFO module in cucumber

Tendril is a morphological innovation during plant evolution, which provides the plants to obtain climbing ability. However, the tendril morphogenesis is poorly understood. A novel tendril morphogenesis defective mutant (tmd1) was identified in cucumber. The apical part of tendril was replaced by a leaf blade in tmd1 mutant, and it lost the climbing ability. Map-based cloning, qPCR detection, bioinformatic analysis, yeast one-hybrid assay, electrophoretic mobility shift assay, and luciferase assay were used to explore the molecular mechanism of CsaTMD1 in regulating tendril morphogenesis. CsaUFO was the candidate causal gene, and a fragment deletion within promoter impaired CsaUFO expression in tmd1 mutant. A conserved motif 1, which harbored two putative TCP transcription factor binding sites, was located within this deleted fragment. CsaTEN directly bound the motif 1 and positively regulated CsaUFO, and mutation in motif 1 removed this regulation. Our work shows a CsaTEN-CsaUFO module in regulating tendril morphogenesis, indicating that evolution of tendril in cucumber due to simply drive of CsaUFO by CsaTEN in tendril. Additionally, the conserved motif 1 provides a strategy for engineering tendril-less Cucurbitaceae crops.

SHOOT MERISTEMLESS participates in the heterophylly of Hygrophila difformis (Acanthaceae)

In heterophyllous plants, leaf shape shows remarkable plasticity in response to environmental conditions. However, transgenic studies of heterophylly are lacking and the molecular mechanism remains unclear. Here, we cloned the KNOTTED1-LIKE HOMEOBOX family gene SHOOT MERISTEMLESS (STM) from the heterophyllous plant Hygrophila difformis (Acanthaceae). We used molecular, morphogenetic, and biochemical tools to explore its functions in heterophylly. HdSTM was detected in different organs of H. difformis, and its expression changed with environmental conditions. Heterologous, ectopic expression of HdSTM in Arabidopsis (Arabidopsis thaliana) increased leaf complexity and CUP-SHAPED COTYLEDON (CUC) transcript levels. However, overexpression of HdSTM in H. difformis did not induce the drastic leaf change in the terrestrial condition. Overexpression of HdSTM in H. difformis induced quick leaf variations in submergence, while knockdown of HdSTM led to disturbed leaf development and weakened heterophylly in H. difformis. HdCUC3 had the same spatiotemporal expression pattern as HdSTM. Biochemical analysis revealed a physical interaction between HdSTM and HdCUC3. Our results provide genetic evidence that HdSTM is involved in regulating heterophylly in H. difformis.

Bignonieae (Bignoniaceae) from the Pico do Jabre, Paraíba, Brazil: Taxonomic diversity and distribution

Abstract The tribe Bignonieae with approximately 393 species, represents the largest tribe of Bignoniaceae. Most members of Bignonieae are tendrillate lianas, although some shrubs are also found within this clade. The Pico do Jabre, located at 1,197 m of altitude, represents the highest mountain in the state of Paraíba (Brazil) and an area of extreme biological importance. We conducted an inventory of the Bignonieae from the Pico do Jabre. We documented eight genera and 13 species, only Tanaecium parviflorum is a shrub. The most diverse genera recorded are: Tanaecium (3 spp.), Amphilophium (2 spp.), Bignonia (2 spp.) and Xylophragma (2 spp.). Anemopaegma, Cuspidaria, Dolichandra and Pyrostegia are represented by a single species each. Six species are new records for the region (i.e., Bignonia ramentacea, B. sciuripabulum, Tanaecium cyrtanthum, T. dichotomum, Xylophragma harleyi and X. heterocalyx). Tanaecium cyrtanthum, X. harleyi and X. heterocalyx are new records for the state of Paraíba. Prior to this study, Xylophragma heterocalyx was only known from the type specimen, from Minas Gerais, representing a new record for the Caatinga. The high number of new records found in this study highlights the importance of regional floristic inventories for the documentation of new species occurrences.

Reaching the top through a tortuous path: helical growth in climbing plants

Climbing plants have voluble organs, for example, tendrils and modified stems, which twine up neighboring plants to reach the canopy. These organs perform exaggerated circumnutation, during which they grow towards the shaded areas of the forest (skototropism) to find a host. In response to mechanical stimulus, they grow towards the support (thigmotropism), tailoring their development to firmly attach to it (thigmomorphogenesis). The underlying molecular pathways of these crucial mechanisms are virtually unknown. Here, we review current progress on molecular regulation of the development and growth of climber's voluble organs. Recent advances in the subject point epigenetics and sensory biology as the emerging frontiers in the study of climbing plant's growth and functioning. We briefly review new developments on the molecular basis of plants' mechanosensory system, discussing the findings in the context of the climbing habit.

Phylotranscriptomics in Cucurbitaceae Reveal Multiple Whole-Genome Duplications and Key Morphological and Molecular Innovations

The ability of climbing plants to grow upward along others to reach the canopy for photosynthesis is hypothesized as a key innovation in flowering plants. Most members of the Cucurbitaceae, a family containing ∼1000 species and many important crops, are climbers and have characteristic tendrils and pepo fruits. Here, we present 127 newly sequenced transcriptomes and genomes along with other datasets for a total of 136 cucurbits representing all tribes to establish a robust Cucurbitaceae phylogeny containing eight highly resolved major clades. We analyzed whole-genome duplication, diversification dynamics, and ancestral morphologies, and found that after early genome duplication event(s), a burst of diversification and morphological innovations in flower, fruit, and root characters occurred under the climate optimum in the Early Eocene. Species radiation during the Mid-Eocene Climatic Optimum also coincided with several morphological changes shared by 80% of cucurbits. We found that the cucurbit-specific tendril identity gene TEN originated from a paleo-polyploidization event at the origin of the family. Our results support the hypothesis that cucurbit diversifications were probably driven by increased genetic diversity following polyploidizations and by trait morphological innovations under paleo-climate upheavals. Our study provides a phylogenetic framework and new insights into morphological and genomic changes underlying the adaptive evolution of Cucurbitaceae.

The molecular control of tendril development in angiosperms

The climbing habit has evolved multiple times during the evolutionary history of angiosperms. Plants evolved various strategies for climbing, such as twining stems, tendrils and hooks. Tendrils are threadlike organs with the ability to twine around other structures through helical growth; they may be derived from a variety of structures, such as branches, leaflets and inflorescences. The genetic capacity to grow as a tendrilled climber existed in some of the earliest land plants; however, the underlying molecular basis of tendril development has been studied in only a few taxa. Here, we summarize what is known about the molecular basis of tendril development in model and candidate model species from key tendrilled families, that is, Fabaceae, Vitaceae, Cucurbitaceae, Passifloraceae and Bignoniaceae. Studies on tendril molecular genetics and development show the molecular basis of tendril formation and ontogenesis is diverse, even when tendrils have the same ontogenetic origin, for example leaflet-derived tendrils in Fabaceae and Bignoniaceae. Interestingly, all tendrils perform helical growth during contact-induced coiling, indicating that such ability is not correlated with their ontogenetic origin or phylogenetic history. Whether the same genetic networks are involved during helical growth in diverse tendrils still remains to be investigated.

Convergent Evolution and the Diverse Ontogenetic Origins of Tendrils in Angiosperms

Climbers are abundant in tropical forests, where they constitute a major functional plant type. The acquisition of the climbing habit in angiosperms constitutes a key innovation. Successful speciation in climbers is correlated with the development of specialized climbing strategies such as tendrils, i.e., filiform organs with the ability to twine around other structures through helical growth. Tendrils are derived from a variety of morphological structures, e.g., stems, leaves, and inflorescences, and are found in various plant families. In fact, tendrils are distributed throughout the angiosperm phylogeny, from magnoliids to asterids II, making these structures a great model to study convergent evolution. In this study, we performed a thorough survey of tendrils within angiosperms, focusing on their origin and development. We identified 17 tendril types and analyzed their distribution through the angiosperm phylogeny. Some interesting patterns emerged. For instance, tendrils derived from reproductive structures are exclusively found in the Core Eudicots, except from one monocot species. Fabales and Asterales are the orders with the highest numbers of tendrilling strategies. Tendrils derived from modified leaflets are particularly common among asterids, occurring in Polemoniaceae, Bignoniaceae, and Asteraceae. Although angiosperms have a large number of tendrilled representatives, little is known about their origin and development. This work points out research gaps that should help guide future research on the biology of tendrilled species. Additional research on climbers is particularly important given their increasing abundance resulting from environmental disturbance in the tropics.

Complete chloroplast genome sequences contribute to plant species delimitation: A case study of the Anemopaegma species complex

PREMISE OF THE STUDY

Bignoniaceae is an important component of neotropical forests and a model for evolutionary and biogeographical studies. A previous combination of molecular markers and morphological traits improved the phylogeny of the group. Here we demonstrate the value of next-generation sequencing (NGS) to assemble the chloroplast genome of eight Anemopaegma species and solve taxonomic problems.

METHODS

Three NGS platforms were used to sequence total DNA of Anemopaegma species. After genome assembly and annotation, we compared chloroplast genomes within Anemopaegma, with other Lamiales species, and the evolutionary rates of protein-coding genes using Tanaecium tetragonolobum as the outgroup. Phylogenetic analyses of Anemopaegma with different data sets were performed.

KEY RESULTS

Chloroplast genomes of Anemopaegma species ranged from 167,413 bp in A. foetidum to 168,987 bp in A. acutifolium ("typical" form). They exhibited a characteristic quadripartite structure with a large single-copy region (75,070-75,761 bp), a small single-copy region (12,766-12,817 bp) and a pair of inverted repeat regions (IRs) (39,480-40,481) encoding an identical set of 112 genes. An inversion of a fragment with ca. 8 kb, located in the IRs and containing the genes trnI-AAU, ycf2, and trnL-CAA, was observed in these chloroplast genomes when compared with those of other Lamiales.

CONCLUSIONS

Anemopaegma species have the largest genomes within the Lamiales possibly due to the large amount of repetitive sequences and IR expansion. Variation was higher in coding regions than in noncoding regions, and some genes were identified as markers for differentiation between species. The use of the entire chloroplast genome gave better phylogenetic resolution of the taxonomic groups. We found that two forms of A. acutifolium result from different maternal lineages.

Using mustard genomes to explore the genetic basis of evolutionary change

Recent advances in sequencing technologies and gene manipulation tools have driven mustard species into the spotlight of comparative research and have offered powerful insight how phenotypic space is explored during evolution. Evidence emerged for genome-wide signal of transcription factors and gene duplication contributing to trait divergence, e.g., PLETHORA5/7 in leaf complexity. Trait divergence is often manifested in differential expression due to cis-regulatory divergence, as in KNOX genes and REDUCED COMPLEXITY, and can be coupled with protein divergence. Fruit shape in Capsella rubella results from anisotropic growth during three distinct phases. Brassicaceae exhibit novel fruit dispersal strategy, explosive pod shatter, where the rapid movement depends on slow build-up of tension and its rapid release facilitated by asymmetric cell wall thickenings.

Evolutionary Developmental Biology (Evo-Devo) Research in Latin America

Famous for its blind cavefish and Darwin's finches, Latin America is home to some of the richest biodiversity hotspots of our planet. The Latin American fauna and flora inspired and captivated naturalists from the nineteenth and twentieth centuries, including such notable pioneers such as Fritz Müller, Florentino Ameghino, and Léon Croizat who made a significant contribution to the study of embryology and evolutionary thinking. But, what are the historical and present contributions of the Latin American scientific community to Evo-Devo? Here, we provide the first comprehensive overview of the Evo-Devo laboratories based in Latin America and describe current lines of research based on endemic species, focusing on body plans and patterning, systematics, physiology, computational modeling approaches, ecology, and domestication. Literature searches reveal that Evo-Devo in Latin America is still in its early days; while showing encouraging indicators of productivity, it has not stabilized yet, because it relies on few and sparsely distributed laboratories. Coping with the rapid changes in national scientific policies and contributing to solve social and health issues specific to each region are among the main challenges faced by Latin American researchers. The 2015 inaugural meeting of the Pan-American Society for Evolutionary Developmental Biology played a pivotal role in bringing together Latin American researchers eager to initiate and consolidate regional and worldwide collaborative networks. Such networks will undoubtedly advance research on the extremely high genetic and phenotypic biodiversity of Latin America, bound to be an almost infinite source of amazement and fascinating findings for the Evo-Devo community.

Phylogeny and biogeography of Tynanthus Miers (Bignonieae, Bignoniaceae)

The origin of Neotropical biodiversity represents a key question in evolutionary biology. Despite the attempts to decipher the role of ecological and historical factors to present-day distribution patterns, robust phylogenetic studies of Neotropical clades are still needed before a comprehensive picture of the origin of Neotropical biodiversity can be achieved. Tynanthus Miers (Bignonieae, Bignoniaceae) is a well-circumscribed genus of Neotropical lianas with species that are narrowly distributed, except from a few taxa. The genus is characterized by a clove odor, small bilabiate flowers with the two upper lobes almost fused, and fruits with raised margins, all of which represent morphological synapomorphies for this clade. Other distinctive characters are the thecae reflexed forward, the densely pubescent ovaries and the poorly-developed nectariferous disk. The circumscription of the genus has remained constant over the years, despite the problematic limits of most genera of tribe Bignonieae. In this study, we reconstruct the phylogeny of Tynanthus based on two plastid (ndhF and rpl32-trnL) and one nuclear (pepC) markers and use this phylogenetic framework to investigate the biogeographical history of the genus. Our phylogenetic hypothesis provides further support for the monophyly of Tynanthus, and strongly supports a series of infra-generic clades. Most species are reconstructed as monophyletic, while T. cognatus and T. polyanthus are paraphyletic. Biogeographic reconstructions suggest that Tynanthus originated between 9.4 and 21.5Mya, most likely at approximately 15.3Mya. The MRCA of the genus was likely broadly distributed through lowland Amazonia, Western South America and Central America and diversified in the Neotropics during the Miocene. Closely related species are generally distributed within the same biogeographic area, suggesting that niche conservatism has played an important role in the diversification history of the group.