1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom: CONVOLVULACEÆ

In plants, the carotenoid biosynthesis pathway (CBP) is essential for the production of photosynthetic and protective pigments, plant hormones, and visual/olfactory attractants for animal pollinators and seed dispersers. The regulation of carotenoid biosynthesis at the transcriptional level is vitally important for all of these functions and has been the subject of intensive research. Many putative transcriptional regulators, both direct and indirect, have been identified through conventional mutant analysis, transcriptome profiling, yeast one-hybrid screening, and candidate gene approaches. Despite this progress, our understanding of the transcriptional regulation of carotenoid biosynthesis remains fragmented and incomplete. Frequently, a stimulus or regulator is known, but the mechanism by which it affects transcription has not been elucidated. In other cases, mechanisms have been proposed (such as direct binding of a CBP gene promoter by a transcription factor), but function was tested only in vitro or in heterologous systems, making it unclear whether these proteins actually play a role in carotenoid regulation in their endogenous environments. Even in cases where the mechanism is relatively well understood, regulators are often studied in isolation, either in a single plant species or outside the context of other known regulators. This presents a conundrum: why so many candidate regulators but so little consensus? Here we summarize current knowledge on transcriptional regulation of the CBP, lay out the challenges contributing to this conundrum, identify remaining knowledge gaps, and suggest future research directions to address these challenges and knowledge gaps.

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Transcriptional Regulation of Carotenoid Biosynthesis in Plants: So Many Regulators, So Little Consensus

Toward the 'golden' era: The status in uncovering the regulatory control of carotenoid accumulation in plants.

Abstract Carotenoids are isoprenoid metabolites synthesized de novo in all photosynthetic organisms. Carotenoids are essential for plants with diverse functions in photosynthesis, photoprotection, pigmentation, phytohormone synthesis, and signaling. They are also critically important for humans as precursors of vitamin A synthesis and as dietary antioxidants. The vital roles of carotenoids to plants and humans have prompted significant progress toward our understanding of carotenoid metabolism and regulation. New regulators and novel roles of carotenoid metabolites are continuously revealed. This review focuses on current status of carotenoid metabolism and highlights recent advances in comprehension of the intrinsic and multi-dimensional regulation of carotenoid accumulation. We also discuss the functional evolution of carotenoids, the agricultural and horticultural application, and some key areas for future research. 

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Plant carotenoids: recent advances and future perspectives

Carotenoid Pigment Accumulation in Horticultural Plants

Little is known about the factors regulating carotenoid biosynthesis in flowers. Here, we characterized the REDUCED CAROTENOID PIGMENTATION2 (RCP2) locus from two monkeyflower (Mimulus) species, the bumblebee-pollinated species Mimulus lewisii and the hummingbird-pollinated species Mimulus verbenaceus We show that loss-of-function mutations of RCP2 cause drastic down-regulation of the entire carotenoid biosynthetic pathway. The causal gene underlying RCP2 encodes a tetratricopeptide repeat protein that is closely related to the Arabidopsis (Arabidopsis thaliana) REDUCED CHLOROPLAST COVERAGE proteins. RCP2 appears to regulate carotenoid biosynthesis independently of RCP1, a previously identified R2R3-MYB master regulator of carotenoid biosynthesis. We show that RCP2 is necessary and sufficient for chromoplast development and carotenoid accumulation in floral tissues. Simultaneous down-regulation of RCP2 and two closely related paralogs, RCP2-L1 and RCP2-L2, yielded plants with pale leaves deficient in chlorophyll and carotenoids and with reduced chloroplast compartment size. Finally, we demonstrate that M. verbenaceus is just as amenable to chemical mutagenesis and in planta transformation as the more extensively studied M. lewisii, making these two species an excellent platform for comparative developmental genetics studies of closely related species with dramatic phenotypic divergence.

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A Tetratricopeptide Repeat Protein Regulates Carotenoid Biosynthesis and Chromoplast Development in Monkeyflowers (Mimulus).

The incredible diversity of floral color and pattern in nature is largely determined by the transcriptional regulation of anthocyanin and carotenoid biosynthetic genes. While the transcriptional control of anthocyanin biosynthesis is well understood, little is known about the factors regulating the carotenoid biosynthetic pathway in flowers. Here, we characterize the Reduced Carotenoid Pigmentation 2 (RCP2) locus from two monkeyflower ( Mimulus ) species, the bumblebee-pollinated M. lewisii and hummingbird-pollinated M. verbenaceus . We show that loss-of-function mutations of RCP2 cause drastic down-regulation of the entire carotenoid biosynthetic pathway in these species. Through bulk segregant analysis and transgenic experiments, we have identified the causal gene underlying RCP2 , encoding a tetratricopeptide repeat (TPR) protein that is closely related to the Arabidopsis Reduced Chloroplast Coverage (REC) proteins. RCP2 appears to regulate carotenoid biosynthesis independently of RCP1, a previously identified R2R3-MYB master regulator of carotenoid biosynthesis. We show that RCP2 is required for chromoplast development and suggest that it most likely regulates the expression of carotenoid biosynthetic genes through chromoplast-to-nucleus retrograde signaling. Furthermore, we demonstrate that M. verbenaceus is just as amenable to chemical mutagenesis and in planta transformation as the more extensively studied M. lewisii , making these two species an excellent platform for comparative developmental genetics studies of two closely related species with dramatic phenotypic divergence.

/pdf/a-tetratricopeptide-repeat-protein-regulates-carotenoid-5b4p8hgxfx.pdf

A Tetratricopeptide Repeat Protein Regulates Carotenoid Biosynthesis and Chromoplast Development in Monkeyflowers (Mimulus)

Single-gene overdominance is one of the major mechanisms proposed to explain heterosis (i.e., hybrid vigor), the phenomenon that hybrid offspring between two inbred lines or varieties show superior phenotypes to both parents. Although sporadic examples of single-gene overdominance have been reported over the decades, the molecular nature of this phenomenon remains poorly understood and it is unclear whether any generalizable principle underlies the various cases. Through bulk segregant analysis, chemical profiling, and transgenic experiments, we show that loss-of-function alleles of the FLAVONE SYNTHASE (FNS) gene cause overdominance in anthocyanin-based flower color intensity in the monkeyflower species Mimulus lewisii FNS negatively affects flower color intensity by competing with the anthocyanin biosynthetic enzymes for the same substrates, yet positively affects flower color intensity by producing flavones, the colorless copigments required for anthocyanin stabilization, leading to enhanced pigmentation in the heterozyote (FNS/fns) relative to both homozygotes (FNS/FNS and fns/fns). We suggest that this type of antagonistic pleiotropy (i.e., alleles with opposing effects on different components of the phenotypic output) might be a general principle underlying single-gene overdominance.

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Shilin Chen

Papers

A Tetratricopeptide Repeat Protein Regulates Carotenoid Biosynthesis and Chromoplast Development in Monkeyflowers (Mimulus).

A Tetratricopeptide Repeat Protein Regulates Carotenoid Biosynthesis and Chromoplast Development in Monkeyflowers (Mimulus)

Molecular Basis of Overdominance at a Flower Color Locus.