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The modification of fertile stamens into sterile staminodes has occurred independently many times in the flowering plant lineage. In the genus Aquilegia (columbine) and its closest relatives, the two stamen whorls closest to the carpels have been converted to staminodes. In Aquilegia, the only genetic analyses of staminode development have been reverse genetic approaches revealing that B-class floral identity genes are involved. A. jonesii, the only species of columbine where staminodes have reverted to fertile stamens, allows us to explore the genetic architecture of staminode development using a forward genetic approach. We performed QTL analysis using an outcrossed F2 population between A. jonesii and a horticultural variety that makes fully developed staminodes, A. coerulea 'Origami'. Our results reveal a polygenic basis for staminode loss where the two staminode whorls are under some level of independent control. We also discovered that staminode loss in A. jonesii is not complete, in which staminode-like traits sometimes occur in the inner fertile stamens, potentially representing a fading boundary of gene expression. The QTLs identified in this study provide a map to guide future reverse genetic and functional studies examining the genetic basis and evolutionary significance of this trait.

Floral organs are produced by floral meristems (FMs), which harbor stem cells in their centers. Since each flower only has a finite number of organs, the stem cell activity of an FM will always terminate at a specific time point, a process termed floral meristem termination (FMT). Variation in the timing of FMT can give rise to floral morphological diversity, but how this process is fine-tuned at a developmental and evolutionary level is poorly understood. Flowers from the genus Aquilegia share identical floral organ arrangement except for stamen whorl number (SWN), making Aquilegia a well-suited system for investigation of this process: differences in SWN between species represent differences in the timing of FMT. By crossing A. canadensis and A. brevistyla, quantitative trait locus (QTL) mapping has revealed a complex genetic architecture with seven QTL. We explored potential candidate genes under each QTL and characterized novel expression patterns of select loci of interest using in situ hybridization. To our knowledge, this is the first attempt to dissect the genetic basis of how natural variation in the timing of FMT is regulated, and our results provide insight into how floral morphological diversity can be generated at the meristematic level.

The evolution of novel features, such as eyes or wings, that allow organisms to exploit their environment in new ways can lead to increased diversification rates. Therefore, understanding the genetic and developmental mechanisms involved in the origin of these key innovations has long been of interest to evolutionary biologists. In flowering plants, floral nectar spurs are a prime example of a key innovation, with the independent evolution of spurs associated with increased diversification rates in multiple angiosperm lineages due to their ability to promote reproductive isolation via pollinator specialization. As none of the traditional plant model taxa have nectar spurs, little is known about the genetic and developmental basis of this trait. Nectar spurs are a defining feature of the columbine genus Aquilegia (Ranunculaceae), a lineage that has experienced a relatively recent and rapid radiation. We use a combination of genetic mapping, gene expression analyses, and functional assays to identify a gene crucial for nectar spur development, POPOVICH (POP), which encodes a C2H2 zinc-finger transcription factor. POP plays a central role in regulating cell proliferation in the Aquilegia petal during the early phase (phase I) of spur development and also appears to be necessary for the subsequent development of nectaries. The identification of POP opens up numerous avenues for continued scientific exploration, including further elucidating of the genetic pathway of which it is a part, determining its role in the initial evolution of the Aquilegia nectar spur, and examining its potential role in the subsequent evolution of diverse spur morphologies across the genus.

BackgroundPetal nectar spurs, which facilitate pollination through animal attraction and pollen placement, represent a key innovation promoting diversification in the genus Aquilegia (Ranunculaceae). Identifying the genetic components that contribute to the development of these three-dimensional structures will inform our understanding of the number and types of genetic changes that are involved in the evolution of novel traits. In a prior study, gene expression between two regions of developing petals, the laminar blade and the spur cup, was compared at two developmental stages in the horticultural variety A. coerulea 'Origami'. Several hundred genes were differentially expressed (DE) between the blade and spur at both developmental stages. In order to narrow in on a set of genes crucial to early spur formation, the current study uses RNA sequencing (RNAseq) to conduct comparative expression analyses of petals from five developmental stages between four Aquilegia species, three with morphologically variable nectar spurs, A. sibirica, A. formosa, and A. chrysantha, and one that lacks nectar spurs, A. ecalcarata.ResultsPetal morphology differed increasingly between taxa across the developmental stages assessed, with petals from all four taxa being indistinguishable pre-spur formation at developmental stage 1 (DS1) and highly differentiated by developmental stage 5 (DS5). In all four taxa, genes involved in mitosis were down-regulated over the course of the assessed developmental stages, however, many genes involved in mitotic processes remained expressed at higher levels later in development in the spurred taxa. A total of 690 genes were identified that were consistently DE between the spurred taxa and A. ecalcarata at all five developmental stages. By comparing these genes with those identified as DE between spur and blade tissue in A. coerulea 'Origami', a set of only 35 genes was identified that shows consistent DE between petal samples containing spur tissue versus those without spur tissue.ConclusionsThe results of this study suggest that expression differences in very few loci are associated with the presence and absence of spurs. In general, it appears that the spurless petals of A. ecalcarata cease cell divisions and enter the cell differentiation phase at an earlier developmental time point than those that produce spurs. This much more tractable list of 35 candidates genes will greatly facilitate targeted functional studies to assess the genetic control and evolution of petal spurs in Aquilegia.

The columbine genus Aquilegia is a classic example of an adaptive radiation, involving a wide variety of pollinators and habitats. Here we present the genome assembly of A. coerulea 'Goldsmith', complemented by high-coverage sequencing data from 10 wild species covering the world-wide distribution. Our analyses reveal extensive allele sharing among species and demonstrate that introgression and selection played a role in the Aquilegia radiation. We also present the remarkable discovery that the evolutionary history of an entire chromosome differs from that of the rest of the genome - a phenomenon that we do not fully understand, but which highlights the need to consider chromosomes in an evolutionary context.

Members of the sucrose non-fermenting related kinase Group2 (SnRK2) subclasses are implicated in both direct and indirect abscisic acid (ABA) response pathways. We have used phylogenetic, biochemical, and transient in vivo approaches to examine interactions between Triticum tauschii protein kinase 1 (TtPK1) and an interacting protein, Oryza sativa SnRK2-calcium sensor (OsSCS1). Given that TtPK1 has 100% identity with its rice ortholog, osmotic stress/ABA-activated protein kinase (OsSAPK2), we hypothesized that the SCS and TtPK1 interactions are present in both wheat and rice. Here, we show that SnRK2s are clearly divided into four pan-angiosperm clades with those in the traditionally defined Subclass II encompassing two distinct clades (OsSAPK1/2 and OsSAPK3), although OsSAPK3 lacks an Arabidopsis ortholog. We also show that SCSs are distinct from a second lineage, that we term SCSsister, and while both clades pre-date land plants, the SCSsister clade lacks Poales representatives. Our Y2H assays revealed that the removal of the OsSCS1 C-terminal region along with its N-terminal EF-hand abolished its interaction with the kinase. Using transient in planta bimolecular fluorescence complementation experiments, we demonstrate that TtPK1/OsSCS1 dimerization co-localizes with DAPI-stained nuclei and with FM4-64-stained membranes. Finally, OsSCS1- and OsSAPK2-hybridizing transcripts co-accumulate in shoots/coleoptile of drying seedlings, consistent with up-regulated kinase transcripts of PKABA1 and TtPK1. Our studies suggest that interactions between homologs of the SnRK2 and SCS lineages are broadly conserved across angiosperms and offer new directions for investigations of related proteins.

Flowers of the lower eudicot Aquilegia (columbine) possess morphological innovations, namely elaborate petal spurs and a fifth distinct organ identity, the staminodium, that are well suited to the investigation of key questions in developmental evolution. The recent evolution of these characteristics combined with a growing set of genetic and genomic resources has provided insight into how the traits arose and diversified. The petal spur appears to represent a key innovation that diversified largely via modification of specific aspects of cell expansion. In the case of the staminodium, gene duplication has played a role in allowing a novel organ identity to be carved out of the traditional ABC program.

The Ranunculales are a hyperdiverse lineage in many aspects of their phenotype, including growth habit, floral and leaf morphology, reproductive mode, and specialized metabolism. Many Ranunculales species, such as opium poppy and goldenseal, have a high medicinal value. In addition, the order includes a large number of commercially important ornamental plants, such as columbines and larkspurs. The phylogenetic position of the order with respect to monocots and core eudicots and the diversity within this lineage make the Ranunculales an excellent group for studying evolutionary processes by comparative studies. Lately, the phylogeny of Ranunculales was revised, and genetic and genomic resources were developed for many species, allowing comparative analyses at the molecular scale. Here, we review the literature on the resources for genetic manipulation and genome sequencing, the recent phylogeny reconstruction of this order, and its fossil record. Further, we explain their habitat range and delve into the diversity in their floral morphology, focusing on perianth organ identity, floral symmetry, occurrences of spurs and nectaries, sexual and pollination systems, and fruit and dehiscence types. The Ranunculales order offers a wealth of opportunities for scientific exploration across various disciplines and scales, to gain novel insights into plant biology for researchers and plant enthusiasts alike. [ABSTRACT FROM AUTHOR]