Cis-regulatory variation expands the colour palette of the Brassicaceae.

This article comments on: Ye S, Hua S, Ma T, Ma X, Chen Y, Wu L, Zhao L, Yi B, Ma C, Tu J, Shen J, Fu T, Wen J. 2022. Genetic and multi-omics analyses reveal BnaA07.PAP2In-184-317 as the key gene conferring anthocyanin-based color in Brassica napus flowers. Journal of Experimental Botany 73,6630–6645.</jats:p

Joining the dots.

It is hypothesised that morphological evolution occurs through a variety of molecular mechanisms. Position and patterning of petal spots in Clarkia evolved through changes to the regulatory region of a gene encoding the transcriptional activator of pigment synthesis, prompting its regulation by novel positional cues

AGAMOUS mediates timing of guard cell formation during gynoecium development

In Arabidopsis thaliana, stomata are composed of two guard cells that control the aperture of a central pore to facilitate gas exchange between the plant and its environment, which is particularly important during photosynthesis. Although leaves are the primary photosynthetic organs of flowering plants, floral organs are also photosynthetically active. In the Brassicaceae, evidence suggests that silique photosynthesis is important for optimal seed oil content. A group of transcription factors containing MADS DNA binding domains is necessary and sufficient to confer floral organ identity. Elegant models, such as the ABCE model of flower development and the floral quartet model, have been instrumental in describing the molecular mechanisms by which these floral organ identity proteins govern flower development. However, we lack a complete understanding of how the floral organ identity genes interact with the underlying leaf development program. Here, we show that the MADS domain transcription factor AGAMOUS (AG) represses stomatal development on the gynoecial valves, so that maturation of stomatal complexes coincides with fertilization. We present evidence that this regulation by AG is mediated by direct transcriptional repression of a master regulator of the stomatal lineage, MUTE, and show data that suggests this interaction is conserved among several members of the Brassicaceae. This work extends our understanding of the mechanisms underlying floral organ formation and provides a framework to decipher the mechanisms that control floral organ photosynthesis

The phylogenetic history of the<i>Gorteria diffusa</i>radiation sheds light on the origins of plant sexual deception

The morphologically diverse daisy species Gorteria diffusa employs varying levels of sexually deceptive pollination. The species comprises at least fifteen spatially and phenotypically discrete floral morphotypes that are associated with a range of pollination strategies, from generalism to highly specialised sexual deception involving visual mimicry of females of the bee-fly Megapalpus capensis . However, the pattern of evolution of the unique floral traits in this lineage remains unknown because the phylogenetic history of the closely related floral morphotypes has proved unresolvable using traditional approaches. Here we apply genotyping-by-sequencing (GBS), a reduced representation sequencing technology that has significantly increased the tractability of phylogenetic problems involving recent radiations, to the recalcitrant phylogenetic problem of Gorteria across its South African distribution. Population genomic analyses show that individuals group according to morphotype, irrespective of geographic proximity, highlighting the distinctiveness of the morphotypes at the genetic level. We resolve the phylogenetic history of the closely related morphotypes, demonstrating that they are mostly well supported monophyletic entities that are grouped into at least three distinct geographically separated clades. Our results suggest that both incomplete lineage sorting and introgression across geographical clades have previously hindered reconstruction of the phylogeny of this species complex that has diversified rapidly during the Quaternary. Sexual deception is a phylogenetically derived pollination strategy within the complex that evolved at least twice, and was likely achieved by sequential evolution of a set of floral traits that in combination elicit sexual responses from the bee-fly pollinator. While insight into the evolution of sexual deception has been limited by strong phylogenetic conservatism of this strategy in other plant lineages, our results both provide the framework, and confirm the utility of G. diffusa , for further understanding the genetic pathways and selective pressures underlying the complex phenotypes required to exploit insect mating behaviour for pollination

Confocal and epifluorescence imaging of <i>MUTEpro</i>:<i>MUTE-GFP</i> in L-<i>er</i> and <i>ag-10</i> backgrounds.

(A-F) Images of early stage 12 gynoecial valves of MUTEpro:MUTE-GFP in (A-C) a wild-type L-er background and (D-F) an ag-10 background using confocal microscopy. Arrowheads indicate the presence of fluorescent foci. (G-O) Images of MUTEpro:MUTE-GFP (G-L) stage 11 gynoecia in (G-I) a wild-type L-er background, (J-L) an ag-10 background, and (M-O) stage 12 gynoecia in a wild-type L-er background. Each panel is a sample from a different plant. Scale is 100 μm. (TIF)</p

Transcriptional response of master regulators of stomatal development to repression of <i>AG</i> activity.

(A-B) Levels of mRNAs encoding stomatal bHLH transcription factor regulators, as determined by RT-qPCR, in (A) ag-10 stage 10–13 gynoecia relative to L-er stage 10–13 gynoecia, (B) dexamethasone-treated AG-amiRNAi (OPpro:AG-amiRNA/35Spro:GR-LhG4) in stage 10–13 gynoecia relative to mock-treated AG-amiRNAi in stage 10–13 gynoecia 24 h after treatments. Each dot in (A-B) represents the technical mean of an individual independent biological replicate. (C-E) Levels of (C) SPCH, (D) MUTE, and (E) FAMA mRNAs during gynoecium development as determined by RT-qPCR. Data for L-er is the same as in Fig 2I but was originally paired with the ag-10 experiments presented in this figure. Errors bars are s.e.m. of four independent biological replicates (F) Levels of SPCH, MUTE, FAMA, and AG mRNAs, as determined by RT-qPCR, in stage 13 gynoecia after treatment with dexamethasone relative to untreated (0 d) in stage 13 gynoecia. “Day after DEX” indicates the number of days that gynoecia were treated with DEX before being harvested at anthesis (stage 13), with “0 d” representing the untreated sample. “Stage at DEX” indicates the approximate stage of the flower/gynoecium when DEX treatment was applied. Error bars are s.e.m of three independent biological replicates. (G-J) Maximum intensity projections of stitched confocal laser scanning z-stack micrographs of (G, I) stage 12 and (H, J) stage 13 gynoecia from plants harboring a FAMApro:2xYFP transgene in (G-H) L-er and ag-10 backgrounds, and (I-J) the AG-amiRNAi (OPpro:AG-amiRNA/35Spro:GR-LhG4) background before treatment (0 h) and after dexamethasone treatment (48 h and 72 h). YFP is colored green and chlorophyll fluorescence is colored magenta. Scale bars for images of whole gynoecia are 100 μm. Scale bars for insets are 20 μm.</p

Multiple gene co-options underlie the rapid evolution of sexually deceptive flowers in Gorteria diffusa.

Gene co-option, the redeployment of an existing gene in an unrelated developmental context, is an important mechanism underlying the evolution of morphological novelty. In most cases described to date, novel traits emerged by co-option of a single gene or genetic network. Here, we show that the integration of multiple co-opted genetic elements facilitated the rapid evolution of complex petal spots that mimic female bee-fly pollinators in the sexually deceptive South African daisy Gorteria diffusa. First, co-option of iron homeostasis genes altered petal spot pigmentation, producing a color similar to that of female pollinators. Second, co-option of the root hair gene GdEXPA7 enabled the formation of enlarged papillate petal epidermal cells, eliciting copulation responses from male flies. Third, co-option of the miR156-GdSPL1 transcription factor module altered petal spot placement, resulting in better mimicry of female flies resting on the flower. The three genetic elements were likely co-opted sequentially, and strength of sexual deception in different G. diffusa floral forms strongly correlates with the presence of the three corresponding morphological alterations. Our findings suggest that gene co-options can combine in a modular fashion, enabling rapid evolution of novel complex traits

Confocal imaging of AG-GFP in late-stage gynoecia.

(A-C) Maximum intensity projections of stitched confocal laser scanning z-stack micrographs of (A) early stage 12, (B) late stage 12, and (C) stage 13 gynoecia from AGpro:AG-GFP ag-1 plants. Arrowheads indicate accumulation of AG-GFP in the replum. Scale is 100 μm. (TIF)</p

Sequences of probes used for gel shift assays.

In Arabidopsis thaliana, stomata are composed of two guard cells that control the aperture of a central pore to facilitate gas exchange between the plant and its environment, which is particularly important during photosynthesis. Although leaves are the primary photosynthetic organs of flowering plants, floral organs are also photosynthetically active. In the Brassicaceae, evidence suggests that silique photosynthesis is important for optimal seed oil content. A group of transcription factors containing MADS DNA binding domains is necessary and sufficient to confer floral organ identity. Elegant models, such as the ABCE model of flower development and the floral quartet model, have been instrumental in describing the molecular mechanisms by which these floral organ identity proteins govern flower development. However, we lack a complete understanding of how the floral organ identity genes interact with the underlying leaf development program. Here, we show that the MADS domain transcription factor AGAMOUS (AG) represses stomatal development on the gynoecial valves, so that maturation of stomatal complexes coincides with fertilization. We present evidence that this regulation by AG is mediated by direct transcriptional repression of a master regulator of the stomatal lineage, MUTE, and show data that suggests this interaction is conserved among several members of the Brassicaceae. This work extends our understanding of the mechanisms underlying floral organ formation and provides a framework to decipher the mechanisms that control floral organ photosynthesis.</div

Statistical analysis of counts of fluorescent foci after repression of <i>AG</i> activity.

Statistical analysis of counts of fluorescent foci after repression of AG activity.</p