Conservation vs divergence in LEAFY and APETALA1 functions between Arabidopsis thaliana and Cardamine hirsuta

Transcriptomic and metabolomic profiling reveals molecular regulatory network involved in flower development and phenotypic changes in two Lonicera macranthoides varieties

Due to the medicinal importance of the flowers of Xianglei type (XL) Lonicera macranthoides, it is important to understand the molecular mechanisms that underlie their development. In this study, we elucidated the transcriptomic and metabolomic mechanisms that underlie the flower development mechanism of two L. macranthoides varieties. In this study, 3435 common differentially expressed unigenes (DEGs) and 1138 metabolites were identified. These common DEGs were mainly enriched in plant hormone signal transduction pathways. Metabolomic analysis showed that amino acids were the main metabolites of differential accumulation in wild-type (WT) L. macranthoides, whereas in XL, they were flavonoids and phenylalanine metabolites. Genes and transcription factors (TFs), such as MYB340, histone deacetylase 1 (HDT1), small auxin-up RNA 32 (SAUR32), auxin response factor 6 (ARF6), PIN-LIKES 7 (PILS7), and WRKY6, likely drive metabolite accumulation. Plant hormone signals, especially auxin signals, and various TFs induce downstream flower organ recognition genes, resulting in a differentiation of the two L. macranthoides varieties in terms of their developmental trajectories. In addition, photoperiodic, autonomous, and plant hormone pathways jointly regulated the L. macranthoides corolla opening. SAUR32, Arabidopsis response regulator 9 (ARR9), Gibberellin receptor (GID1B), and Constans-like 10 (COL10) were closely related to the unfolding of the L. macranthoides corolla. These findings offer valuable understanding of the flower growth process of L. macranthoides and the excellent XL phenotypes at the molecular level.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04019-1.

Leaf form diversity and evolution: a never-ending story in plant biology

Leaf form can vary at different levels, such as inter/intraspecies, and diverse leaf shapes reflect their remarkable ability to adapt to various environmental conditions. Over the past two decades, considerable progress has been made in unraveling the molecular mechanisms underlying leaf form diversity, particularly the regulatory mechanisms of leaf complexity. However, the mechanisms identified thus far are only part of the entire process, and numerous questions remain unanswered. This review aims to provide an overview of the current understanding of the molecular mechanisms driving leaf form diversity while highlighting the existing gaps in our knowledge. By focusing on the unanswered questions, this review aims to shed light on areas that require further research, ultimately fostering a more comprehensive understanding of leaf form diversity.

Rewiring of a KNOXI regulatory network mediated by UFO underlies the compound leaf development in Medicago truncatula

Class I KNOTTED-like homeobox (KNOXI) genes are parts of the regulatory network that control the evolutionary diversification of leaf morphology. Their specific spatiotemporal expression patterns in developing leaves correlate with the degrees of leaf complexity between simple-leafed and compound-leafed species. However, KNOXI genes are not involved in compound leaf formation in several legume species. Here, we identify a pathway for dual repression of MtKNOXI function in Medicago truncatula. PINNATE-LIKE PENTAFOLIATA1 (PINNA1) represses the expression of MtKNOXI, while PINNA1 interacts with MtKNOXI and sequesters it to the cytoplasm. Further investigations reveal that UNUSUAL FLORAL ORGANS (MtUFO) is the direct target of MtKNOXI, and mediates the transition from trifoliate to pinnate-like pentafoliate leaves. These data suggest a new layer of regulation for morphological diversity in compound-leafed species, in which the conserved regulators of floral development, MtUFO, and leaf development, MtKNOXI, are involved in variation of pinnate-like compound leaves in M. truncatula.

Control of compound leaf patterning by MULTI-PINNATE LEAF1 (MPL1) in chickpea

Plant lateral organs are often elaborated through repetitive formation of developmental units, which progress robustly in predetermined patterns along their axes. Leaflets in compound leaves provide an example of such units that are generated sequentially along the longitudinal axis, in species-specific patterns. In this context, we explored the molecular mechanisms underlying an acropetal mode of leaflet initiation in chickpea pinnate compound leaf patterning. By analyzing naturally occurring mutants multi-pinnate leaf1 (mpl1) that develop higher-ordered pinnate leaves with more than forty leaflets, we show that MPL1 encoding a C2H2-zinc finger protein sculpts a morphogenetic gradient along the proximodistal axis of the early leaf primordium, thereby conferring the acropetal leaflet formation. This is achieved by defining the spatiotemporal expression pattern of CaLEAFY, a key regulator of leaflet initiation, and also perhaps by modulating the auxin signaling pathway. Our work provides novel molecular insights into the sequential progression of leaflet formation.

Temperature-responsive module of OfAP1 and OfLFY regulates floral transition and floral organ identity in Osmanthus fragrans

The MADS-box transcription factor APETELA1 (AP1) is crucially important for reproductive developmental processes. The function of AP1 and the classic LFY-AP1 interaction in woody plants are not widely known. Here, the OfAP1-a gene from the continuously flowering plant Osmanthus fragrans 'Sijigui' was characterized, and its roles in regulating flowering time, petal number robustness and floral organ identity were determined using overexpression in Arabidopsis thaliana and Nicotiana tabacum. The expression of OfAP1-a was significantly induced by low ambient temperature and was upregulated with the floral transition process. Ectopic expression OfAP1-a revealed its classic function in flowering and flower ABC models. The expression of OfAP1-a is inhibited by LEAFY (OfLFY) through direct promoter binding, as confirmed by yeast one-hybrid and dual luciferase assays. Arabidopsis plants overexpressing OfAP1-a exhibited accelerated flowering and altered floral organ identities. Moreover, OfAP1-a-overexpressing plants displayed variable petal numbers. Likewise, the overexpression of OfLFY in Arabidopsis and Nicotiana altered petal number robustness and inflorescence architecture, partially by regulating native AP1 in transformed plants. Furthermore, we performed RNA-seq analysis of transgenic Nicotiana plants. DEGs were identified by transcriptome analysis, and we found that the expression of several floral homeotic genes was altered in both OfAP1-a and OfLFY-overexpressing transgenic lines. Our results suggest that OfAP1-a may play important roles during floral transition and development in response to ambient temperature. OfAP1-a functions as a petal number modulator and may directly activate a subset of flowers to regulate floral organ formation. OfAP1-a and OfLFY mutually regulate the expression of each other and coregulate genes that might be involved in these phenotypes related to flowering. The results provide valuable data for understanding the function of the LFY-AP1 module in the reproductive process and shaping floral structures in woody plants.

BrrA02.LMI1 Encodes a Homeobox Protein That Affects Leaf Margin Development in Brassica rapa

Leaf margin morphology is an important quality trait affecting the commodity and environmental adaptability of crops. Brassica rapa is an ideal research material for exploring the molecular mechanisms underlying leaf lobe development. Here, we identified BrrA02.LMI1 to be a promising gene underlying the QTL qBrrLLA02 controlling leaf lobe formation in B. rapa, which was detected in our previous study. Sequence comparison analysis showed that the promoter divergences were the most obvious variations of BrrA02.LMI1 between parental lines. The higher expression level and promoter activity of BrrA02.LMI1 in the lobe-leafed parent indicated that promoter variations of BrrA02.LMI1 were responsible for elevating expression and ultimately causing different allele effects. Histochemical GUS staining indicated that BrrA02.LMI1 is mainly expressed at the leaf margin, with the highest expression at the tip of each lobe. Subcellular localization results showed that BrrA02.LMI1 was in the nucleus. The ectopic expression of BrrA02.LMI1 in A. thaliana resulted in a deep leaf lobe in the wild-type plants, and lobed leaf formation was disturbed in BrrA02.LMI11-downregulated plants. Our findings revealed that BrrA02.LMI1 plays a vital role in regulating the formation of lobed leaves, providing a theoretical basis for the selection and breeding of leaf-shape-diverse varieties of B. rapa.

Promoter variations in a homeobox gene, BrLMI1, contribute to leaf lobe formation in Brassica rapa ssp. chinensis Makino

Key message BrLMI1 is a positive regulatory factor of leaf lobe formation in non-heading Chinese cabbage, and cis-regulatory variations lead to the phenotype of lobed or entire leaf margins.Abstract Leaves are the main consumed organ in leafy non-heading Chinese cabbage (Brassica rapa L. ssp. chinensis Makino), and the shape of the leaves is an important economic trait. However, the molecular regulatory mechanism underlying the lobed-leaf trait in non-heading Chinese cabbage remains unclear. Here, we identified a stable incompletely dominant major locus, qLLA10, for lobed leaf formation in non-heading Chinese cabbage. Based on map-based cloning strategies, BrLMI1, a LATE MERISTEM IDENTITY1 (LMI1)-like gene, was predicted as the candidate gene for qLLA10. Genotyping analysis showed that promoter variations of BrLMI1 in the two parents are responsible for elevating the expression in the lobed-leaf parent and ultimately causing the difference in leaf shape between the two parents, and the promoter activity of BrLMI1 was significantly affected by the promoter variations. BrLMI1 was exclusively localized in the nucleus and expressed mainly at the tip of each lobe. Leaf lobe development was perturbed in BrLMI1-silenced plants produced by virus-induced gene silencing assays, and ectopic overexpression of BrLMI1 in Arabidopsis led to deeply lobed leaves never seen in the wild type, which indicates that BrLMI1 is required for leaf lobe formation in non-heading Chinese cabbage. These findings suggested that BrLMI1 is a positive regulatory factor of leaf lobe formation in non-heading Chinese cabbage and that cis-regulatory variations lead to the phenotype of lobed or entire leaf margins, thus providing a theoretical basis for unraveling the molecular mechanism underlying the lobed leaf phenotype in Brassica crops.

Roles and evolution of four LEAFY homologs in floral patterning and leaf development in woodland strawberry

The plant-specific transcription factor LEAFY (LFY), generally maintained as a single-copy gene in most angiosperm species, plays critical roles in flower development. The woodland strawberry (Fragaria vesca) possesses four LFY homologs in the genome; however, their respective functions and evolution remain unknown. Here, we identified and validated that mutations in one of the four LFY homologs, FveLFYa, cause homeotic conversion of floral organs and reiterative outgrowth of ectopic flowers. In contrast to FveLFYa, FveLFYb/c/d appear dispensable under normal growth conditions, as fvelfyc mutants are indistinguishable from wild type and FveLFYb and FveLFYd are barely expressed. Transgenic analysis and yeast one-hybrid assay showed that FveLFYa and FveLFYb, but not FveLFYc and FveLFYd, are functionally conserved with AtLFY in Arabidopsis (Arabidopsis thaliana). Unexpectedly, LFY-binding site prediction and yeast one-hybrid assay revealed that the transcriptional links between LFY and the APETALA1 (AP1) promoter/the large AGAMOUS (AG) intron are missing in F. vesca, which is due to the loss of LFY-binding sites. The data indicate that mutations in cis-regulatory elements could contribute to LFY evolution. Moreover, we showed that FveLFYa is involved in leaf development, as approximately 30% of mature leaves have smaller or fewer leaflets in fvelfya. Phylogenetic analysis indicated that LFY homologs in Fragaria species may arise from recent duplication events in their common ancestor and are undergoing convergent gene loss. Together, these results provide insight into the role of LFY in flower and leaf development in strawberry and have important implications for the evolution of LFY.

Molecular mechanisms underlying leaf development, morphological diversification, and beyond

The basic mechanisms of leaf development have been revealed through a combination of genetics and intense analyses in select model species. The genetic basis for diversity in leaf morphology seen in nature is also being unraveled through recent advances in techniques and technologies related to genomics and transcriptomics, which have had a major impact on these comparative studies. However, this has led to the emergence of new unresolved questions about the mechanisms that generate the diversity of leaf form. Here, we provide a review of the current knowledge of the fundamental molecular genetic mechanisms underlying leaf development with an emphasis on natural variation and conserved gene regulatory networks involved in leaf development. Beyond that, we discuss open questions/enigmas in the area of leaf development, how recent technologies can best be deployed to generate a unified understanding of leaf diversity and its evolution, and what untapped fields lie ahead.

PaNAC089 is a membrane-tethered transcription factor (MTTF) that modulates flowering, chlorophyll breakdown and trichome initiation

Flowering and senescence are essential developmental stages of green plants, which are governed by complex molecular regulatory networks. However, the connection between flowering regulation and senescence regulation in London plane tree (Platanus acerifolia ) remains unknown. In this study, we identified a gene PaNAC089 from London plane tree, which encodes a membrane-tethered transcription factor (MTTF) belonging to the NAC (NAM, ATAF1/2, CUC2) transcription factor family. We investigated the functions of PaNAC089 in the regulation of flowering and senescence through the analysis of expression profiles and transgenic phenotypes. Heterologous overexpression of ΔPaNAC089 delayed flowering and inhibited chlorophyll breakdown to produce dark green rosette leaves in Arabidopsis . In addition, the trichome density of rosette leaves was decreased in transgenic lines. In ΔPaNAC089 overexpression plants, a series of functional genes with inhibited expression were identified by quantitative real-time polymerase chain reaction (qRT-PCR), including genes that regulate flowering, chlorophyll decomposition, and trichome initiation. Furthermore, Δ PaNAC089 directly binds to the promoter of CONSTANS (CO ) and NON-YELLOWING2 (NYE2 ) in the yeast one-hybrid assay. Consistent with this, luciferase (LUC) transient expression assays also showed that Δ PaNAC089 could inhibit the activity of NYE2 . To summarise, our data suggests that PaNAC089 is an MTTF that modulates flowering, chlorophyll breakdown and trichome initiation.

Imaging flowers: a guide to current microscopy and tomography techniques to study flower development

Developmental biology relies heavily on our ability to generate three-dimensional images of live biological specimens through time, and to map gene expression and hormone response in these specimens as they undergo development. The last two decades have seen an explosion of new bioimaging technologies that have pushed the limits of spatial and temporal resolution and provided biologists with invaluable new tools. However, plant tissues are difficult to image, and no single technology fits all purposes; choosing between many bioimaging techniques is not trivial. Here, we review modern light microscopy and computed projection tomography methods, their capabilities and limitations, and we discuss their current and potential applications to the study of flower development and fertilization.

Flowering time and the identification of floral marker genes in Solanum tuberosum ssp. andigena

Solanaceae is a family of flowering plants that includes agricultural species such as tomato (Solanum lycopersicum), eggplant (S. melongena), pepper (Capsicum annuum), and potato (S. tuberosum). The transition from the vegetative to reproductive stage has been extensively investigated in tomato as it affects fruit yield. While potato has mainly been studied with regards to the formation of storage organs, control of flowering time is a subject of increasing interest as development of true seeds is becoming more important for future breeding strategies. Here, we describe a robust growth regime for synchronized development of S. tuberosum ssp. andigena. Using SEM to analyse the developmental stages of the shoot apical meristem (SAM) throughout the floral transition, we show that andigena is a facultative long-day plant with respect to flowering. In addition, we identify the flower meristem identity gene MACROCALYX (StMC) as a marker to distinguish between the vegetative and reproductive stages. We show that the expression of WUSCHEL HOMEOBOX 9 (StWOX9) and ANANTHA (StAN) are specific to the inflorescence meristem and flower meristems in the cyme, respectively. The expression patterns of homologs of Arabidopsis flowering-time regulators were studied, and indicated that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (StSOC1) and StFD might regulate flowering similar to other plant species.

Investigation into the underlying regulatory mechanisms shaping inflorescence architecture in Chenopodium quinoa

Background

Inflorescence architecture is denoted by the spatial arrangement of various lateral branches and florets formed on them, which is shaped by a complex of regulators. Unveiling of the regulatory mechanisms underlying inflorescence architecture is pivotal for improving crop yield potential. Quinoa (Chenopodium quinoa Willd), a pseudo cereal originated from Andean region of South America, has been widely recognized as a functional super food due to its excellent nutritional elements. Increasing worldwide consumption of this crop urgently calls for its yield improvement. However, dissection of the regulatory networks underlying quinoa inflorescence patterning is lacking.

Results

In this study, we performed RNA-seq analysis on quinoa inflorescence samples collected from six developmental stages, yielding a total of 138.8 GB data. We screened 21,610 differentially expressed genes (DEGs) among all the stages through comparative analysis. Weighted Gene Co-Expression Network Analysis (WGCNA) was performed to categorize the DEGs into ten different modules. Subsequently, we placed emphasis on investigating the modules associated with none branched and branched inflorescence samples. We manually refined the coexpression networks with stringent edge weight cutoffs, and generated core networks using transcription factors and key inflorescence architecture related genes as seed nodes. The core networks were visualized and analyzed by Cytoscape to obtain hub genes in each network. Our finding indicates that the specific occurrence of B3, TALE, WOX, LSH, LFY, GRAS, bHLH, EIL, DOF, G2-like and YABBY family members in early reproductive stage modules, and of TFL, ERF, bZIP, HD-ZIP, C2H2, LBD, NAC, C3H, Nin-like and FAR1 family members in late reproductive stage modules, as well as the several different MADS subfamily members identified in both stages may account for shaping quinoa inflorescence architecture.

Conclusion

In this study we carried out comparative transcriptome analysis of six different stages quinoa inflorescences, and using WGCNA we obtained the most highly potential central hubs for shaping inflorescence. The data obtained from this study will enhance our understanding of the gene network regulating quinoa inflorescence architecture, as well will supply with valuable genetic resources for high-yield elite breeding in the future.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6027-0) contains supplementary material, which is available to authorized users.

CoNekT: an open-source framework for comparative genomic and transcriptomic network analyses

The recent accumulation of gene expression data in the form of RNA sequencing creates unprecedented opportunities to study gene regulation and function. Furthermore, comparative analysis of the expression data from multiple species can elucidate which functional gene modules are conserved across species, allowing the study of the evolution of these modules. However, performing such comparative analyses on raw data is not feasible for many biologists. Here, we present CoNekT (Co-expression Network Toolkit), an open source web server, that contains user-friendly tools and interactive visualizations for comparative analyses of gene expression data and co-expression networks. These tools allow analysis and cross-species comparison of (i) gene expression profiles; (ii) co-expression networks; (iii) co-expressed clusters involved in specific biological processes; (iv) tissue-specific gene expression; and (v) expression profiles of gene families. To demonstrate these features, we constructed CoNekT-Plants for green alga, seed plants and flowering plants (Picea abies, Chlamydomonas reinhardtii, Vitis vinifera, Arabidopsis thaliana, Oryza sativa, Zea mays and Solanum lycopersicum) and thus provide a web-tool with the broadest available collection of plant phyla. CoNekT-Plants is freely available from http://conekt.plant.tools, while the CoNekT source code and documentation can be found at https://github.molgen.mpg.de/proost/CoNekT/.

Ectopic Expression of a Fagopyrum esculentum APETALA1 Ortholog only Rescues Sepal Development in Arabidopsis ap1 Mutant

Fagopyrum esculentum (Polygonaceae: Caryophyllales) exhibits an undifferentiated perianth comprising five showy tepals, which does not completely correspond to the perianth differentiated into typical sepals and petals in most core eudicots. In Arabidopsis, the APETALA1 (AP1) gene is involved in specifying sepals and petals development. Here we isolated AP1 ortholog, FaesAP1, and a 2.2kb FaesAP1 promoter (pFaesAP1) from F. esculentum. FaesAP1 expression is mainly detectable in all floral organs and maintains at a high level when tepals elongate rapidly both in pin and thrum flowers. Moreover, the GUS reporter gene driven by pFaesAP1 was activated in flowers where the sepals were intense, but the petals very weak or absent. Additionally, FaesAP1 ectopic expression in Arabidopsis ap1-10 mutant rescues sepal development fully, obviously prompting early flowering, but failing to complement petal development. In this study, evidence was provided that the showy tepals in the F. esculentum are homologs to core eudicots sepals. Furthermore, these findings show a different perianth identity program in Caryophyllales, suggesting that AP1 orthologs involved in petal development may evolve independently across different clades of core eudicots. Our results also suggest that FaesAP1 holds potential for biotechnical engineering to develop early flowering varieties of F. esculentum.

Genetic control of compound leaf development in the mungbean (Vigna radiata L.)

Many studies suggest that there are distinct regulatory processes controlling compound leaf development in different clades of legumes. Loss of function of the LEAFY (LFY) orthologs results in a reduction of leaf complexity to different degrees in inverted repeat-lacking clade (IRLC) and non-IRLC species. To further understand the role of LFY orthologs and the molecular mechanism in compound leaf development in non-IRLC plants, we studied leaf development in unifoliate leaf (un) mutant, a classical mutant of mungbean (Vigna radiata L.), which showed a complete conversion of compound leaves into simple leaves. Our analysis revealed that UN encoded the mungbean LFY ortholog (VrLFY) and played a significant role in leaf development. In situ RNA hybridization results showed that STM-like KNOXI genes were expressed in compound leaf primordia in mungbean. Furthermore, increased leaflet number in heptafoliate leaflets1 (hel1) mutants was demonstrated to depend on the function of VrLFY and KNOXI genes in mungbean. Our results suggested that HEL1 is a key factor coordinating distinct processes in the control of compound leaf development in mungbean and its related non-IRLC legumes.

LEAFY maintains apical stem cell activity during shoot development in the fern Ceratopteris richardii

During land plant evolution, determinate spore-bearing axes (retained in extant bryophytes such as mosses) were progressively transformed into indeterminate branching shoots with specialized reproductive axes that form flowers. The LEAFY transcription factor, which is required for the first zygotic cell division in mosses and primarily for floral meristem identity in flowering plants, may have facilitated developmental innovations during these transitions. Mapping the LEAFY evolutionary trajectory has been challenging, however, because there is no functional overlap between mosses and flowering plants, and no functional data from intervening lineages. Here, we report a transgenic analysis in the fern Ceratopteris richardii that reveals a role for LEAFY in maintaining cell divisions in the apical stem cells of both haploid and diploid phases of the lifecycle. These results support an evolutionary trajectory in which an ancestral LEAFY module that promotes cell proliferation was progressively co-opted, adapted and specialized as novel shoot developmental contexts emerged.

The first plants colonized land around 500 million years ago. These plants had simple shoots with no branches, similar to the mosses that live today. Later on, some plants evolved more complex structures including branched shoots and flowers (collectively known as the “flowering plants”). Ferns are a group of plants that evolved midway between the mosses and flowering plants and have branched shoots but no flowers.

The gradual transition from simple to more complex plant structures required changes to the way in which cells divide and grow within plant shoots. Whereas animals produce new cells throughout their body, most plant cells divide in areas known as meristems. All plants grow from embryos, which contain meristems that will form the roots and shoots of the mature plant. A gene called LEAFY is required for cells in moss embryos to divide. However, in flowering plants LEAFY does not carry out this role, instead it is only required to make the meristems that produce flowers.

How did LEAFY transition from a general role in embryos to a more specialized role in making flowers? To address this question, Plackett, Conway et al. studied the two LEAFY genes in a fern called Ceratopteris richardii. The experiments showed that at least one of these LEAFY genes was active in the meristems of fern shoots throughout the lifespan of the plant. The shoots of ferns with less active LEAFY genes could not form the leaves seen in normal C. richardii plants. This suggests that as land plants evolved, the role of LEAFY changed from forming embryos to forming complex shoot structures.

Most of our major crops are flowering plants. By understanding how the role of LEAFY has changed over the evolution of land plants, it might be possible to manipulate LEAFY genes in crop plants to alter shoot structures to better suit specific environments.

The role of APETALA1 in petal number robustness

Invariant floral forms are important for reproductive success and robust to natural perturbations. Petal number, for example, is invariant in Arabidopsis thaliana flowers. However, petal number varies in the closely related species Cardamine hirsuta, and the genetic basis for this difference between species is unknown. Here we show that divergence in the pleiotropic floral regulator APETALA1 (AP1) can account for the species-specific difference in petal number robustness. This large effect of AP1 is explained by epistatic interactions: A. thaliana AP1 confers robustness by masking the phenotypic expression of quantitative trait loci controlling petal number in C. hirsuta. We show that C. hirsuta AP1 fails to complement this function of A. thaliana AP1, conferring variable petal number, and that upstream regulatory regions of AP1 contribute to this divergence. Moreover, variable petal number is maintained in C. hirsuta despite sufficient standing genetic variation in natural accessions to produce plants with four-petalled flowers.