Virus-induced gene silencing of the alkaloid-producing basal eudicot model plant Eschscholzia californica (California Poppy)

Advancing virus-induced gene silencing in sunflower: key factors of VIGS spreading and a novel simple protocol

Virus-Induced Gene Silencing (VIGS) is a versatile tool in plant science, yet its application to non-model species like sunflower demands extensive optimization due to transformation challenges. In this study, we aimed to elucidate the factors that significantly affect the efficiency of Agrobacterium-VIGS in sunflowers. After testing a number of approaches, we concluded that the seed vacuum technique followed by 6 h of co-cultivation produced the most efficient VIGS results. Genotype-dependency analysis revealed varying infection percentages (62-91%) and silencing symptom spreading in different sunflower genotypes. Additionally, we explored the mobility of tobacco rattle virus (TRV) and phenotypic silencing manifestation (photo-bleaching) across different tissues and regions of VIGS-infected sunflower plants. We showed the presence of TRV is not necessarily limited to tissues with observable silencing events. Finally, time-lapse observation demonstrated a more active spreading of the photo-bleached spots in young tissues compared to mature ones. This study not only offers a robust VIGS protocol for sunflowers but also provides valuable insights into genotype-dependent responses and the dynamic nature of silencing events, shedding light on TRV mobility across different plant tissues.

The Role of INAPERTURATE POLLEN1 as a Pollen Aperture Factor Is Conserved in the Basal Eudicot Eschscholzia californica (Papaveraceae)

Pollen grains show an enormous variety of aperture systems. What genes are involved in the aperture formation pathway and how conserved this pathway is in angiosperms remains largely unknown. INAPERTURATE POLLEN1 (INP1) encodes a protein of unknown function, essential for aperture formation in Arabidopsis, rice and maize. Yet, because INP1 sequences are quite divergent, it is unclear if their function is conserved across angiosperms. Here, we conducted a functional study of the INP1 ortholog from the basal eudicot Eschscholzia californica (EcINP1) using expression analyses, virus-induced gene silencing, pollen germination assay, and transcriptomics. We found that EcINP1 expression peaks at the tetrad stage of pollen development, consistent with its role in aperture formation, which occurs at that stage, and showed, via gene silencing, that the role of INP1 as an important aperture factor extends to basal eudicots. Using germination assays, we demonstrated that, in Eschscholzia, apertures are dispensable for pollen germination. Our comparative transcriptome analysis of wild-type and silenced plants identified over 900 differentially expressed genes, many of them potential candidates for the aperture pathway. Our study substantiates the importance of INP1 homologs for aperture formation across angiosperms and opens up new avenues for functional studies of other aperture candidate genes.

Virus-induced gene silencing: empowering genetics in non-model organisms

Virus-induced gene silencing (VIGS) is an RNA interference-based technology used to transiently knock down target gene expression by utilizing modified plant viral genomes. VIGS can be adapted to many angiosperm species that cover large phylogenetic distances, allowing the analysis of gene functions in species that are not amenable to stable genetic transformation. With a vast amount of sequence information already available and even more likely to become available in the future, VIGS provides a means to analyze the functions of candidate genes identified in large genomic or transcriptomic screens. Here, we provide a comprehensive overview of target species and VIGS vector systems, assess recent key publications in the field, and explain how plant viruses are modified to serve as VIGS vectors. As many reports on the VIGS technique are being published, we also propose minimal reporting guidelines for carrying out these experiments, with the aim of increasing comparability between experiments. Finally, we propose methods for the statistical evaluation of phenotypic results obtained with VIGS-treated plants, as analysis is challenging due to the predominantly transient nature of the silencing effect.

Insights into carotenoid accumulation using VIGS to block different steps of carotenoid biosynthesis in petals of California poppy

Viral-induced gene silencing of selected biosynthetic genes decreased overall carotenoid accumulation in California poppy. Regulation of carotenogenesis was linked with pigment sequestration, not changes in biosynthetic gene expression. Genes of carotenogenesis are well described, but understanding how they affect carotenoid accumulation has proven difficult because of plant lethality when the pigments are lacking. Here, we used a Tobacco Rattle Virus-based virus-induced-gene-silencing (VIGS) approach in California poppy (Eschscholzia californica) to investigate how silencing of the carotenoid biosynthetic pathway genes affects carotenoid metabolite accumulation and RNA transcript abundance of the carotenoid biosynthetic pathway genes. VIGS of upstream (PDS and ZDS) and downstream (βOH and ZEP) genes reduced transcript abundance of the targeted genes in the poppy petals while having no effect on abundance of the other carotenogenesis genes. Silencing of PDS, ZDS, βOH and ZEP genes reduced total pigment concentration by 75-90% and altered petal colour. HPLC and LC-MS measurements suggested that petal colour changes were caused by substantially altered pigment profiles and quantity. Carotenoid metabolites were different to those normally detected in wild-type petals accumulated but overall carotenoid concentration was less, suggesting the chemical form of carotenoid was important for whether it could be stored at high amounts. In poppy petals, eschscholtzxanthin and retro-carotene-triol were the predominant carotenoids, present mainly as esters. Specific esterification enzymes for specific carotenoids and/or fatty acids appear key for enabling petal carotenoids to accumulate to high amounts. Our findings argue against a direct role for carotenoid metabolites regulating carotenogenesis genes in the petals of California poppy as transcript abundance of carotenogenesis genes studied was unchanged, while the petal carotenoid metabolite profile changed substantially.

Evolving Ideas on the Origin and Evolution of Flowers: New Perspectives in the Genomic Era

The origin of the flower was a key innovation in the history of complex organisms, dramatically altering Earth's biota. Advances in phylogenetics, developmental genetics, and genomics during the past 25 years have substantially advanced our understanding of the evolution of flowers, yet crucial aspects of floral evolution remain, such as the series of genetic and morphological changes that gave rise to the first flowers; the factors enabling the origin of the pentamerous eudicot flower, which characterizes ∼70% of all extant angiosperm species; and the role of gene and genome duplications in facilitating floral innovations. A key early concept was the ABC model of floral organ specification, developed by Elliott Meyerowitz and Enrico Coen and based on two model systems,Arabidopsis thalianaandAntirrhinum majus Yet it is now clear that these model systems are highly derived species, whose molecular genetic-developmental organization must be very different from that of ancestral, as well as early, angiosperms. In this article, we will discuss how new research approaches are illuminating the early events in floral evolution and the prospects for further progress. In particular, advancing the next generation of research in floral evolution will require the development of one or more functional model systems from among the basal angiosperms and basal eudicots. More broadly, we urge the development of "model clades" for genomic and evolutionary-developmental analyses, instead of the primary use of single "model organisms." We predict that new evolutionary models will soon emerge as genetic/genomic models, providing unprecedented new insights into floral evolution.

Tinkering with transcription factor networks for developmental robustness of Ranunculales flowers

BACKGROUND

The flowers of core eudicots and monocots are generally determined by the number of floral organs they produce, and their developmental set-up tolerates little change from the bauplan once the floral primordium is initiated. Many species outside the core eudicots and monocots are more plastic in the number of floral organs they produce. For example, the Nymphaeales (water lilies), within the basal angiosperms, arrange their floral organs spirally and show smooth transitions between floral organs, and many Ranunculales (buttercups) produce variable numbers of stamens by adjusting the number of stamen whorls generated from a specialized ring meristem. However, the interactions of regulatory genes governing those processes are unknown.

SCOPE AND CONCLUSIONS

This review provides an overview of the functional analyses of floral homeotic genes carried out in Ranunculales, summarizing knockdown and mutant phenotypes, and protein interactions to identify similarities and differences within the Ranunculales and in comparison with core eudicots. Floral gene regulatory networks in Ranunculales are identified showing intensive re-wiring amongst the floral homeotic genes to allow some degree of plasticity. The 'fading-border' model of floral organ identity evolution is extended by a hypothesis on how developmental plasticity can be achieved by interdependent regulation of floral homeotic genes. One aspect of floral plasticity may be achieved by regulation of the activity of a stamen-generating ring meristem and first ideas on its control are presented. While the amazing conservation of the major floral organ identity programme is being unravelled by analysing floral homeotic gene function and expression, we are only just beginning to understand the evolution of the gene network governing the organ identity genes, e.g. how plasticity can be achieved, and which aspects foster the robustness of the core eudicot floral bauplan.