MADS-box genes and crop domestication: the jack of all traits

A SEPALLATA MADS-Box Transcription Factor, SlMBP21, Functions as a Negative Regulator of Flower Number and Fruit Yields in Tomato

MADS-box transcription factors act as the crucial regulators in plant organ differentiation. Crop yields are highly influenced by the flower number and fruit growth. However, flower identification is a very complex biological process, which involves many cascade regulations. The molecular mechanisms underlying the genetic regulation of flower identification in cultivated plants, such as tomato, are intricate and require further exploration. In this study, we investigated the vital function of a SEPALLATA (SEP) MADS-box gene, SlMBP21, in tomato sympodial inflorescence meristem (SIM) development for the conversion from SIMs to floral meristems (FMs). SlMBP21 transcripts were primarily accumulated in young inflorescence meristem, flowers, sepals, and abscission zones. The Ailsa Craig (AC++) tomato plants with suppressed SlMBP21 mRNA levels using RNAi exhibited a large increase in flower number and fruit yields in addition to enlarged sepals and inhibited abscission zone development. Scanning electron microscopy (SEM) revealed that the maturation of inflorescence meristems (IMs) was repressed in SlMBP21-RNAi lines. RNA-seq and qRT-PCR analyses showed that numerous genes related to the flower development, plant hormone signal transduction, cell cycle, and cell proliferation et al. were dramatically changed in SlMBP21-RNAi lines. Yeast two-hybrid assay exhibited that SlMBP21 can respectively interact with SlCMB1, SFT, JOINTLESS, and MC, which play key roles in inflorescence meristems or FM development. In summary, our data demonstrate that SlMBP21 functions as a key regulator in SIM development and the conversion from SIMs to FMs, through interacting with other regulatory proteins to control the expression of related genes.

Reflections on the ABC model of flower development

The formulation of the ABC model by a handful of pioneer plant developmental geneticists was a seminal event in the quest to answer a seemingly simple question: how are flowers formed? Fast forward 30 years and this elegant model has generated a vibrant and diverse community, capturing the imagination of developmental and evolutionary biologists, structuralists, biochemists and molecular biologists alike. Together they have managed to solve many floral mysteries, uncovering the regulatory processes that generate the characteristic spatio-temporal expression patterns of floral homeotic genes, elucidating some of the mechanisms allowing ABC genes to specify distinct organ identities, revealing how evolution tinkers with the ABC to generate morphological diversity, and even shining a light on the origins of the floral gene regulatory network itself. Here we retrace the history of the ABC model, from its genesis to its current form, highlighting specific milestones along the way before drawing attention to some of the unsolved riddles still hidden in the floral alphabet.

Evolutionary analysis of MADS-box genes in buckwheat species and functional study of FdMADS28 in flavonoid metabolism

The MADS-box gene family is a transcription factor family that is widely expressed in plants. It controls secondary metabolic processes in plants and encourages the development of tissues like roots and flowers. However, the phylogenetic analysis and evolutionary model of MADS-box genes in Fagopyrum species has not been reported yet. This study identified the MADS-box genes of three buckwheat species at the whole genome level, and conducted systematic evolution and physicochemical analysis. The results showed that these genes can be divided into four subfamilies, with fragment duplication being the main way for the gene family expansion. During the domestication process from golden buckwheat to tartary buckwheat and the common buckwheat, the Ka/Ks ratio indicated that most members of the family experienced strong purification selection pressure, and with individual gene pairs experiencing positive selection. In addition, we combined the expression profile data of the MADS genes, mGWAS data, and WGCNA data to mine genes FdMADS28/48/50 that may be related to flavonoid metabolism. The results also showed that overexpression of FdMADS28 could increase rutin content by decreasing Kaempferol pathway content in hairy roots, and increase the resistance and growth of hairy roots to PEG and NaCl. This study systematically analyzed the evolutionary relationship of MADS-box genes in the buckwheat species, and elaborated on the expression patterns of MADS genes in different tissues under biotic and abiotic stresses, laying an important theoretical foundation for further elucidating their role in flavonoid metabolism.

Flowering time: From physiology, through genetics to mechanism

Plant species have evolved different requirements for environmental/endogenous cues to induce flowering. Originally, these varying requirements were thought to reflect the action of different molecular mechanisms. Thinking changed when genetic and molecular analysis in Arabidopsis thaliana revealed that a network of environmental and endogenous signaling input pathways converge to regulate a common set of "floral pathway integrators." Variation in the predominance of the different input pathways within a network can generate the diversity of requirements observed in different species. Many genes identified by flowering time mutants were found to encode general developmental and gene regulators, with their targets having a specific flowering function. Studies of natural variation in flowering were more successful at identifying genes acting as nodes in the network central to adaptation and domestication. Attention has now turned to mechanistic dissection of flowering time gene function and how that has changed during adaptation. This will inform breeding strategies for climate-proof crops and help define which genes act as critical flowering nodes in many other species.

Dosage effect genes modulate grain development in synthesized Triticum durum-Haynaldia villosa allohexaploid

Polyploidization in plants often leads to increased cell size and grain size, which may be affected by the increased genome dosage and transcription abundance. The synthesized Triticum durum (AABB)-Haynaldia villosa (VV) amphiploid (AABBVV) has significantly increased grain size, especially grain length, than the tetraploid and diploid parents. To investigate how polyploidization affects grain development at the transcriptional level, we perform transcriptome analysis using the immature seeds of T. durum, H. villosa, and the amphiploid. The dosage effect genes are contributed more by differentially expressed genes from genome V of H. villosa. The dosage effect genes overrepresent grain development-related genes. Interestingly, the vernalization gene TaVRN1 is among the positive dosage effect genes in the T. durum‒H. villosa and T. turgidum‒Ae. tauschii amphiploids. The expression levels of TaVRN1 homologs are positively correlated with the grain size and weight. The TaVRN1-B1 or TaVRN1-D1 mutation shows delayed florescence, decreased cell size, grain size, and grain yield. These data indicate that dosage effect genes could be one of the important explanations for increased grain size by regulating grain development. The identification and functional validation of dosage effect genes may facilitate the finding of valuable genes for improving wheat yield.

Developmental stages and episode-specific regulatory genes in andromonoecious melon flower development

BACKGROUND AND AIMS

Given the lack of specific studies on floral development in melon (Cucumis melo L.), we carried out an extensive study involving morphological and transcriptomic analyses to characterize floral development in this species.

METHODS

Using an andromonoecious line, we analysed the development of floral buds in male and hermaphrodite flowers with both light microscopy and scanning electron microscopy. Based on flower lengths, we established a correlation between the developmental stages and four main episodes of floral development and conducted an extensive RNA sequencing analysis of these episodes.

KEY RESULTS

We identified 12 stages of floral development, from the appearance of the floral meristems to anthesis. The main structural differences between male and hermaphrodite flowers appeared between stages 6 and 7; later stages of development leading to the formation of organs and structures in both types of flowers were also described. We analysed the gene expression patterns of the four episodes in flower development to find the genes that were specific to each given episode. Among others, we identified genes that defined the passage from one episode to the next according to the ABCDE model of floral development.

CONCLUSIONS

This work combines a detailed morphological analysis and a comprehensive transcriptomic study to enable characterization of the structural and molecular mechanisms that determine the floral development of an andromonoecious genotype in melon. Taken together, our results provide a first insight into gene regulation networks in melon floral development that are crucial for flowering and pollen formation, highlighting potential targets for genetic manipulation to improve crop yield of melon in the future.

Two SEPALLATA MADS-Box Genes, SlMBP21 and SlMADS1, Have Cooperative Functions Required for Sepal Development in Tomato

MADS-box transcription factors have crucial functions in numerous physiological and biochemical processes during plant growth and development. Previous studies have reported that two MADS-box genes, SlMBP21 and SlMADS1, play important regulatory roles in the sepal development of tomato, respectively. However, the functional relationships between these two genes are still unknown. In order to investigate this, we simultaneously studied these two genes in tomato. Phylogenetic analysis showed that they were classified into the same branch of the SEPALLATA (SEP) clade. qRT-PCR displayed that both SlMBP21 and SlMADS1 transcripts are preferentially accumulated in sepals, and are increased with flower development. During sepal development, SlMBP21 is increased but SlMADS1 is decreased. Using the RNAi, tomato plants with reduced SlMBP21 mRNA generated enlarged and fused sepals, while simultaneous inhibition of SlMBP21 and SlMADS1 led to larger (longer and wider) and fused sepals than that in SlMBP21-RNAi lines. qRT-PCR results exhibited that the transcripts of genes relating to sepal development, ethylene, auxin and cell expansion were dramatically changed in SlMBP21-RNAi sepals, especially in SlMBP21-SlMADS1-RNAi sepals. Yeast two-hybrid assay displayed that SlMBP21 can interact with SlMBP21, SlAP2a, TAGL1 and RIN, and SlMADS1 can interact with SlAP2a and RIN, respectively. In conclusion, SlMBP21 and SlMADS1 cooperatively regulate sepal development in tomato by impacting the expression or activities of other related regulators or via interactions with other regulatory proteins.

Unregulated GmAGL82 due to Phosphorus Deficiency Positively Regulates Root Nodule Growth in Soybean

Nitrogen fixation, occurring through the symbiotic relationship between legumes and rhizobia in root nodules, is crucial in sustainable agriculture. Nodulation and soybean production are influenced by low levels of phosphorus stress. In this study, we discovered a MADS transcription factor, GmAGL82, which is preferentially expressed in nodules and displays significantly increased expression under conditions of phosphate (Pi) deficiency. The overexpression of GmAGL82 in composite transgenic plants resulted in an increased number of nodules, higher fresh weight, and enhanced soluble Pi concentration, which subsequently increased the nitrogen content, phosphorus content, and overall growth of soybean plants. Additionally, transcriptome analysis revealed that the overexpression of GmAGL82 significantly upregulated the expression of genes associated with nodule growth, such as GmENOD100, GmHSP17.1, GmHSP17.9, GmSPX5, and GmPIN9d. Based on these findings, we concluded that GmAGL82 likely participates in the phosphorus signaling pathway and positively regulates nodulation in soybeans. The findings of this research may lay the theoretical groundwork for further studies and candidate gene resources for the genetic improvement of nutrient-efficient soybean varieties in acidic soils.

Transcriptional regulation of tomato fruit ripening

An intrinsic and genetically determined ripening program of tomato fruits often depends upon the appropriate activation of tissue- and stage-specific transcription factors in space and time. The past two decades have yielded considerable progress in detailing these complex transcriptional as well as hormonal regulatory circuits paramount to fleshy fruit ripening. This non-linear ripening process is strongly controlled by the MADS-box and NOR family of proteins, triggering a transcriptional response associated with the progression of fruit ripening. Deepening insights into the connection between MADS-RIN and plant hormones related transcription factors, such as ERFs and ARFs, further conjugates the idea that several signaling units work in parallel to define an output fruit ripening transcriptome. Besides these TFs, the role of other families of transcription factors such as MYB, GLK, WRKY, GRAS and bHLH have also emerged as important ripening regulators. Other regulators such as EIN and EIL proteins also determine the transcriptional landscape of ripening fruits. Despite the abundant knowledge of the complex spectrum of ripening networks in the scientific domain, identifying more ripening effectors would pave the way for a better understanding of fleshy fruit ripening at the molecular level. This review provides an update on the transcriptional regulators of tomato fruit ripening.

Advancing tree genomics to future proof next generation orchard production

The challenges facing tree orchard production in the coming years will be largely driven by changes in the climate affecting the sustainability of farming practices in specific geographical regions. Identifying key traits that enable tree crops to modify their growth to varying environmental conditions and taking advantage of new crop improvement opportunities and technologies will ensure the tree crop industry remains viable and profitable into the future. In this review article we 1) outline climate and sustainability challenges relevant to horticultural tree crop industries, 2) describe key tree crop traits targeted for improvement in agroecosystem productivity and resilience to environmental change, and 3) discuss existing and emerging genomic technologies that provide opportunities for industries to future proof the next generation of orchards.

Genome-wide characterization and expression analysis of MADS-box transcription factor gene family in Perilla frutescens

MADS-box transcription factors are widely involved in the regulation of plant growth, developmental processes, and response to abiotic stresses. Perilla frutescens, a versatile plant, is not only used for food and medicine but also serves as an economical oil crop. However, the MADS-box transcription factor family in P. frutescens is still largely unexplored. In this study, a total of 93 PfMADS genes were identified in P. frutescens genome. These genes, including 37 Type I and 56 Type II members, were randomly distributed across 20 chromosomes and 2 scaffold regions. Type II PfMADS proteins were found to contain a greater number of motifs, indicating more complex structures and diverse functions. Expression analysis revealed that most PfMADS genes (more than 76 members) exhibited widely expression model in almost all tissues. The further analysis indicated that there was strong correlation between some MIKCC-type PfMADS genes and key genes involved in lipid synthesis and flavonoid metabolism, which implied that these PfMADS genes might play important regulatory role in the above two pathways. It was further verified that PfMADS47 can effectively mediate the regulation of lipid synthesis in Chlamydomonas reinhardtii transformants. Using cis-acting element analysis and qRT-PCR technology, the potential functions of six MIKCC-type PfMADS genes in response to abiotic stresses, especially cold and drought, were studied. Altogether, this study is the first genome-wide analysis of PfMADS. This result further supports functional and evolutionary studies of PfMADS gene family and serves as a benchmark for related P. frutescens breeding studies.

Genome-Wide Analysis of the MADS-Box Gene Family in Hibiscus syriacus and Their Role in Floral Organ Development

Hibiscus syriacus belongs to the Malvaceae family, and is a plant with medicinal, edible, and greening values. MADS-box transcription factor is a large family of regulatory factors involved in a variety of biological processes in plants. Here, we performed a genome-wide characterization of MADS-box proteins in H. syriacus and investigated gene structure, phylogenetics, cis-acting elements, three-dimensional structure, gene expression, and protein interaction to identify candidate MADS-box genes that mediate petal developmental regulation in H. syriacus. A total of 163 candidate MADS-box genes were found and classified into type I (Mα, Mβ, and Mγ) and type II (MIKC and Mδ). Analysis of cis-acting elements in the promoter region showed that most elements were correlated to plant hormones. The analysis of nine HsMADS expressions of two different H. syriacus cultivars showed that they were differentially expressed between two type flowers. The analysis of protein interaction networks also indicated that MADS proteins played a crucial role in floral organ identification, inflorescence and fruit development, and flowering time. This research is the first to analyze the MADS-box family of H. syriacus and provides an important reference for further study of the biological functions of the MADS-box, especially in flower organ development.

Research advances on the gene regulation of floral development and color in orchids

Orchidaceae is one of the largest monocotyledon families and contributes significantly to worldwide biodiversity, with value in the fields of landscaping, medicine, and ecology. The diverse phenotypes and vibrant colors of orchid floral organs make them excellent research objects for investigating flower development and pigmentation. In recent years, a number of orchid genomes have been published, laying the molecular foundation for revealing flower development and color presentation. In this article, we review transcription factors, the structural genes responsible for the floral pigment synthesis pathways, the molecular mechanisms of flower morphogenesis, and the potential relationship between flower type and flower color. This study provides a theoretical reference for the research on molecular mechanisms related to flower morphogenesis and color presentation, genetic improvement, and new variety creation in orchids.

Evolution of cereal floral architecture and threshability

Hulled grains, while providing natural protection for seeds, pose a challenge to manual threshing due to the pair of glumes tightly encasing them. Based on natural evolution and artificial domestication, gramineous crops evolved various hull-like floral organs. Recently, progress has been made in uncovering novel domesticated genes associated with cereal threshability and deciphering common regulatory modules pertinent to the specification of hull-like floral organs. Here we review morphological similarities, principal regulators, and common mechanisms implicated in the easy-threshing traits of crops. Understanding the shared and unique features in the developmental process of cereal threshability may not only shed light on the convergent evolution of cereals but also facilitate the de novo domestication of wild cereal germplasm resources through genome-editing technologies.

The Soybean Expression Atlas v2: A comprehensive database of over 5000 RNA-seq samples

Soybean is a crucial crop worldwide, used as a source of food, feed, and industrial products due to its high protein and oil content. Previously, the rapid accumulation of soybean RNA-seq data in public databases and the computational challenges of processing raw RNA-seq data motivated us to develop the Soybean Expression Atlas, a gene expression database of over a thousand RNA-seq samples. Over the past few years, our database has allowed researchers to explore the expression profiles of important gene families, discover genes associated with agronomic traits, and understand the transcriptional dynamics of cellular processes. Here, we present the Soybean Expression Atlas v2, an updated version of our database with a fourfold increase in the number of samples, featuring transcript- and gene-level transcript abundance matrices for 5481 publicly available RNA-seq samples. New features in our database include the availability of transcript-level abundance estimates and equivalence classes to explore differential transcript usage, abundance estimates in bias-corrected counts to increase the accuracy of differential gene expression analyses, a new web interface with improved data visualization and user experience, and a reproducible and scalable pipeline available as an R package. The Soybean Expression Atlas v2 is available at https://soyatlas.venanciogroup.uenf.br/, and it will accelerate soybean research, empowering researchers with high-quality and easily accessible gene expression data.

PEP444c encoded within the MIR444c gene regulates microRNA444c accumulation in barley

MicroRNAs are small, noncoding RNA molecules that regulate the expression of their target genes. The MIR444 gene family is present exclusively in monocotyledons, and microRNAs444 from this family have been shown to target certain MADS-box transcription factors in rice and barley. We identified three barley MIR444 (MIR444a/b/c) genes and comprehensively characterised their structure and the processing pattern of the primary transcripts (pri-miRNAs444). Pri-microRNAs444 undergo extensive alternative splicing, generating functional and nonfunctional pri-miRNA444 isoforms. We show that barley pri-miRNAs444 contain numerous open reading frames (ORFs) whose transcripts associate with ribosomes. Using specific antibodies, we provide evidence that selected ORFs encoding PEP444a within MIR444a and PEP444c within MIR444c are expressed in barley plants. Moreover, we demonstrate that CRISPR-associated endonuclease 9 (Cas9)-mediated mutagenesis of the PEP444c-encoding sequence results in a decreased level of PEP444 transcript in barley shoots and roots and a 5-fold reduced level of mature microRNA444c in roots. Our observations suggest that PEP444c encoded by the MIR444c gene is involved in microRNA444c biogenesis in barley.

Structural and Functional Analysis of the MADS-Box Genes Reveals Their Functions in Cold Stress Responses and Flower Development in Tea Plant (Camellia sinensis)

MADS-box genes comprise a large family of transcription factors that play crucial roles in all aspects of plant growth and development. However, no detailed information on the evolutionary relationship and functional characterization of MADS-box genes is currently available for some representative lineages, such as the Camellia plant. In this study, 136 MADS-box genes were detected from a reference genome of the tea plant (Camellia sinensis) by employing a 569 bp HMM (Hidden Markov Model) developed using nucleotide sequencing including 73 type I and 63 type II genes. An additional twenty-seven genes were identified, with five MIKC-type genes. Truncated and/or inaccurate gene models were manually verified and curated to improve their functional characterization. Subsequently, phylogenetic relationships, chromosome locations, conserved motifs, gene structures, and gene expression profiles were systematically investigated. Tea plant MIKC genes were divided into all 14 major eudicot subfamilies, and no gene was found in Mβ. The expansion of MADS-box genes in the tea plant was mainly contributed by WGD/fragment and tandem duplications. The expression profiles of tea plant MADS-box genes in different tissues and seasons were analyzed, revealing widespread evolutionary conservation and genetic redundancy. The expression profiles linked to cold stress treatments suggested the wide involvement of MADS-box genes from the tea plant in response to low temperatures. Moreover, a floral 'ABCE' model was proposed in the tea plant and proved to be both conserved and ancient. Our analyses offer a detailed overview of MADS-box genes in the tea plant, allowing us to hypothesize the potential functions of unknown genes and providing a foundation for further functional characterizations.

Phylogenetically-conserved candidate genes unify biodiversity-ecosystem function relationships and eco-evolutionary dynamics across biological scales

The intra- and interspecific facets of biodiversity have traditionally been analysed separately, limiting our understanding of how evolution has shaped biodiversity, how biodiversity (as a whole) alters ecological dynamics and hence eco-evolutionary feedbacks at the community scale. Here, we propose using candidate genes phylogenetically-conserved across species and sustaining functional traits as an inclusive biodiversity unit transcending the intra- and interspecific boundaries. This framework merges knowledge from functional genomics and functional ecology, and we first provide guidelines and a concrete example for identifying phylogenetically-conserved candidate genes (PCCGs) within communities and for measuring biodiversity from PCCGs. We then explain how biodiversity measured at PCCGs can be linked to ecosystem functions, which unifies recent observations that both intra- and interspecific biodiversity are important for ecosystem functions. We then highlight the eco-evolutionary processes shaping PCCG diversity patterns and argue that their respective role can be inferred from concepts derived from population genetics. Finally, we explain how PCCGs may shift the field of eco-evolutionary dynamics from a focal-species approach to a more realistic focal-community approach. This framework provides a novel perspective to investigate the global ecosystem consequences of diversity loss across biological scales, and how these ecological changes further alter biodiversity evolution.

Genetic mapping and functional analysis of a classical tassel branch number mutant Tp2 in maize

Tassel branch number is a key trait that contributes greatly to grain yield in maize (Zea mays). We obtained a classical mutant from maize genetics cooperation stock center, Teopod2 (Tp2), which exhibits severely decreased tassel branch. We conducted a comprehensive study, including phenotypic investigation, genetic mapping, transcriptome analysis, overexpression and CRISPR knock-out, and tsCUT&Tag of Tp2 gene for the molecular dissection of Tp2 mutant. Phenotypic investigation showed that it is a pleiotropic dominant mutant, which is mapped to an interval of approximately 139-kb on Chromosome 10 harboring two genes Zm00001d025786 and zma-miR156h. Transcriptome analysis showed that the relative expression level of zma-miR156h was significantly increased in mutants. Meanwhile, overexpression of zma-miR156h and knockout materials of ZmSBP13 exhibited significantly decreased tassel branch number, a similar phenotype with Tp2 mutant, suggesting that zma-miR156h is the causal gene of Tp2 and targets ZmSBP13 gene. Besides, the potential downstream genes of ZmSBP13 were uncovered and showed that it may target multiple proteins to regulate inflorescence structure. Overall, we characterized and cloned Tp2 mutant, and proposed a zma-miR156h-ZmSBP13 model functioning in regulating tassel branch development in maize, which is an essential measure to satisfy the increasing demands of cereals.

Molecular evolution, diversification, and expression assessment of MADS gene family in Setaria italica, Setaria viridis, and Panicum virgatum

KEY MESSAGE

This paper sheds light on the evolution and expression patterns of MADS genes in Setaria and Panicum virgatum. SiMADS51 and SiMADS64 maybe involved in the ABA-dependent pathway of drought response. The MADS gene family is a key regulatory factor family that controls growth, reproduction, and response to abiotic stress in plants. However, the molecular evolution of this family is rarely reported. Here, a total of 265 MADS genes were identified in Setaria italica (foxtail millet), Setaria viridis (green millet), and Panicum virgatum (switchgrass) and analyzed by bioinformatics, including physicochemical characteristics, subcellular localization, chromosomal position and duplicate, motif distribution, genetic structure, genetic evolvement, and expression patterns. Phylogenetic analysis was used to categorize these genes into M and MIKC types. The distribution of motifs and gene structure were similar for the corresponding types. According to a collinearity study, the MADS genes have been mostly conserved during evolution. The principal cause of their expansion is segmental duplication. However, the MADS gene family tends to shrink in foxtail millet, green millet, and switchgrass. The MADS genes were subjected to purifying selection, but several positive selection sites were also identified in three species. And most of the promoters of MADS genes contain cis-elements related to stress and hormonal response. RNA-seq and quantitative Real-time PCR (qRT-PCR) analysis also were examined. SiMADS genes expression levels are considerably changed in reaction to various treatments, following qRT-PCR analysis. This sheds fresh light on the evolution and expansion of the MADS family in foxtail millet, green millet, and switchgrass, and lays the foundation for further research on their functions.

Genome-wide analysis of the MADS-box gene family involved in salt and waterlogging tolerance in barley (Hordeum vulgare L.)

MADS-box transcription factors are crucial members of regulatory networks underlying multiple developmental pathways and abiotic stress regulatory networks in plants. Studies on stress resistance-related functions of MADS-box genes are very limited in barley. To gain insight into this gene family and elucidate their roles in salt and waterlogging stress resistance, we performed genome-wide identification, characterization and expression analysis of MADS-box genes in barley. A whole-genome survey of barley revealed 83 MADS-box genes, which were categorized into type I (Mα, Mβ and Mγ) and type II (AP1, SEP1, AGL12, STK, AGL16, SVP and MIKC*) lineages based on phylogeny, protein motif structure. Twenty conserved motifs were determined and each HvMADS contained one to six motifs. We also found tandem repeat duplication was the driven force for HvMADS gene family expansion. Additionally, the co-expression regulatory network of 10 and 14 HvMADS genes was predicted in response to salt and waterlogging stress, and we proposed HvMADS11,13 and 35 as candidate genes for further exploration of the functions in abiotic stress. The extensive annotations and transcriptome profiling reported in this study ultimately provides the basis for MADS functional characterization in genetic engineering of barley and other gramineous crops.

Epistatic interaction between CsCEN and CsSHBY in regulating indeterminate/determinate growth of lateral branch in cucumber

KEY MESSAGE

Two genetic loci, det-ma (CsCEN) and det-lb, showed epistatic interaction on indeterminate/determinate growth of LB in cucumber. CsSHBY was identified as the candidate gene for det-lb locus. Plant architecture depends on the spatial regulation of meristems from both main axis (MA) and lateral branches (LBs). Fate (indeterminate or determinate) of these meristems is a crucial source of architectural diversity determining crop productivity and management. CENTRORADIALIS/TERMINAL FLOWER 1/SELF-PRUNING (CETS) gene family have been well known as pivotal regulators for indeterminate/determinate growth of MA. Nevertheless, genes that regulate LB indeterminacy/determinacy remained unclear. Cucumber (Cucumis sativus L.) has typical monopodial growth and multiple lateral branches. Both MA and LBs had indeterminate or determinate growth, and indeterminate/determinate growth of LB was controlled by two distinct loci, det-ma (CsCEN) and det-lb. In our study, based on bulked segregant analysis (BSA) method, the det-lb locus was mapped on a 60.6 kb region on chromosome 1 harboring only one gene CsaV3_1G044330, which encoded a putative vacuolar-sorting protein (designated as CsSHBY). Multipoint mutations in CsSHBY were identified in D082 and D226, compared with CCMC, including nonsynonymous SNP mutations and a 6-bp deletion in exons. Further, qPCR showed that CsSHBY was highly expressed in lateral bud of CCMC, suggesting that CsSHBY might play an active role in regulating indeterminate/determinate growth of LB. Genetic analyses showed that det-ma (CsCEN) had an epistatic effect on det-lb (CsSHBY), and CsCEN could activate CsSHBY promoter by Dual luciferase and GUS activity assays. Meanwhile, Cscen or Csshby was found to influence auxin contents and CsYUCs and CsPINs expression levels. These findings provided new insights into precisely optimizing plant architecture for yield improvements.

Genome-Wide Identification of MADS-Box Family Genes in Safflower (Carthamus tinctorius L.) and Functional Analysis of CtMADS24 during Flowering

Safflower is an important economic crop with a plethora of industrial and medicinal applications around the world. The bioactive components of safflower petals are known to have pharmacological activity that promotes blood circulation and reduces blood stasis. However, fine-tuning the genetic mechanism of flower development in safflower is still required. In this study, we report the genome-wide identification of MADS-box transcription factors in safflower and the functional characterization of a putative CtMADS24 during vegetative and reproductive growth. In total, 77 members of MADS-box-encoding genes were identified from the safflower genome. The phylogenetic analysis divided CtMADS genes into two types and 15 subfamilies. Similarly, bioinformatic analysis, such as of conserved protein motifs, gene structures, and cis-regulatory elements, also revealed structural conservation of MADS-box genes in safflower. Furthermore, the differential expression pattern of CtMADS genes by RNA-seq data indicated that type II genes might play important regulatory roles in floral development. Similarly, the qRT-PCR analysis also revealed the transcript abundance of 12 CtMADS genes exhibiting tissue-specific expression in different flower organs. The nucleus-localized CtMADS24 of the AP1 subfamily was validated by transient transformation in tobacco using GFP translational fusion. Moreover, CtMADS24-overexpressed transgenic Arabidopsis exhibited early flowering and an abnormal phenotype, suggesting that CtMADS24 mediated the expression of genes involved in floral organ development. Taken together, these findings provide valuable information on the regulatory role of CtMADS24 during flower development in safflower and for the selection of important genes for future molecular breeding programs.

Genome-Wide Analysis of the Mads-Box Transcription Factor Family in Solanum melongena

The MADS-box transcription factors are known to be involved in several aspects of plant growth and development, especially in floral organ specification. However, little is known in eggplant. Here, 120 eggplant MADS-box genes were identified and categorized into type II (MIKCC and MIKC*) and type I (Mα, Mβ, and Mγ) subfamilies based on phylogenetic relationships. The exon number in type II SmMADS-box genes was greater than that in type I SmMADS-box genes, and the K-box domain was unique to type II MADS-box TFs. Gene duplication analysis revealed that segmental duplications were the sole contributor to the expansion of type II genes. Cis-elements of MYB binding sites related to flavonoid biosynthesis were identified in three SmMADS-box promoters. Flower tissue-specific expression profiles showed that 46, 44, 38, and 40 MADS-box genes were expressed in the stamens, stigmas, petals, and pedicels, respectively. In the flowers of SmMYB113-overexpression transgenic plants, the expression levels of 3 SmMADS-box genes were co-regulated in different tissues with the same pattern. Correlation and protein interaction predictive analysis revealed six SmMADS-box genes that might be involved in the SmMYB113-regulated anthocyanin biosynthesis pathway. This study will aid future studies aimed at functionally characterizing important members of the MADS-box gene family.

Deciphering the role of SPL12 and AGL6 from a genetic module that functions in nodulation and root regeneration in Medicago sativa

Our results show that SPL12 plays a crucial role in regulating nodule development in Medicago sativa L. (alfalfa), and that AGL6 is targeted and downregulated by SPL12. Root architecture in plants is critical because of its role in controlling nutrient cycling, water use efficiency and response to biotic and abiotic stress factors. The small RNA, microRNA156 (miR156), is highly conserved in plants, where it functions by silencing a group of SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors. We previously showed that transgenic Medicago sativa (alfalfa) plants overexpressing miR156 display increased nodulation, improved nitrogen fixation and enhanced root regenerative capacity during vegetative propagation. In alfalfa, transcripts of eleven SPLs, including SPL12, are targeted for cleavage by miR156. In this study, we characterized the role of SPL12 in root architecture and nodulation by investigating the transcriptomic and phenotypic changes associated with altered transcript levels of SPL12, and by determining SPL12 regulatory targets using SPL12-silencing and -overexpressing alfalfa plants. Phenotypic analyses showed that silencing of SPL12 in alfalfa caused an increase in root regeneration, nodulation, and nitrogen fixation. In addition, AGL6 which encodes AGAMOUS-like MADS box transcription factor, was identified as being directly targeted for silencing by SPL12, based on Next Generation Sequencing-mediated transcriptome analysis and chromatin immunoprecipitation assays. Taken together, our results suggest that SPL12 and AGL6 form a genetic module that regulates root development and nodulation in alfalfa.

FaesAP3_1 Regulates the FaesELF3 Gene Involved in Filament-Length Determination of Long-Homostyle Fagopyrum esculentum

The identification downstream genes of floral organ identity regulators are critical to revealing the molecular mechanisms underlying floral morphogenesis. However, a general regulatory pathway between floral organ identity genes and their downstream targets is still unclear because of the lack of studies in nonmodel species. Here, we screened a direct downstream target gene, FaesELF3, of a stamen identity transcription factor, FaesAP3_1, in long-homostyle (LH) Fagopyrum esculentum moench by using yeast one-hybrid (Y1H) and dual-luciferase reporter (DR) assays. Furthermore, FaesAP3_1-silenced LH plants that produced flowers with part stamens or anthers homeotically converted into a tepaloid structure, and FaesELF3-silenced plants that had flowers with part stamens consisting of a short filament and empty anther (male sterile anther). All these suggested that transcription factor (TF) FaesAP3_1 directly activates FaesELF3 in order to regulate filament elongation and pollen grain development in LH buckwheat. Our data also suggested that other stamen development pathways independent of FaesAP3_1 remain in F. esculentum.

Genome-Wide Identification, Evolution, and Expression Characterization of the Pepper (Capsicum spp.) MADS-box Gene Family

MADS domain transcription factors play roles throughout the whole lifecycle of plants from seeding to flowering and fruit-bearing. However, systematic research into MADS-box genes of the economically important vegetable crop pepper (Capsicum spp.) is still lacking. We identified 174, 207, and 72 MADS-box genes from the genomes of C. annuum, C. baccatum, and C. chinense, respectively. These 453 MADS-box genes were divided into type I (Mα, Mβ, Mγ) and type II (MIKC* and MIKC^C) based on their phylogenetic relationships. Collinearity analysis identified 144 paralogous genes and 195 orthologous genes in the three Capsicum species, and 70, 114, and 10 MADS-box genes specific to C. annuum, C. baccatum, and C. chinense, respectively. Comparative genomic analysis highlighted functional differentiation among homologous MADS-box genes during pepper evolution. Tissue expression analysis revealed three main expression patterns: highly expressed in roots, stems, leaves, and flowers (CaMADS93/CbMADS35/CcMADS58); only expressed in roots; and specifically expressed in flowers (CaMADS26/CbMADS31/CcMADS11). Protein interaction network analysis showed that type II CaMADS mainly interacted with proteins related to flowering pathway and flower organ development. This study provides the basis for an in-depth study of the evolutionary features and biological functions of pepper MADS-box genes.

Genetic studies on continuous flowering in woody plant Osmanthus fragrans

Continuous flowering is a key horticultural trait in ornamental plants, whereas the specific molecular regulation mechanism remains largely unknown. In sweet osmanthus (Osmanthus fragrans Lour.), plants based on their flowering characteristics are divided into once-flowering (OF) habit and continuous flowering (CF) habit. Here, we first described the flowering phenology shifts of OF and CF habits in sweet osmanthus through paraffin section and microscope assay. Phenotypic characterization showed that CF plants had constant new shoot growth, floral transition, and blooming for 1 year, which might lead to a continuous flowering trait. We performed the transcriptome sequencing of OF and CF sweet osmanthus and analyzed the transcriptional activity of flowering-related genes. Among the genes, three floral integrators, OfFT, OfTFL1, and OfBFT, had a differential expression during the floral transition process in OF and CF habits. The expression patterns of the three genes in 1 year were revealed. The results suggested that their accumulations corresponded to the new shoots occurring and the floral transition process. Function studies suggested that OfFT acted as a flowering activator, whereas OfBFT was a flowering inhibitor. Yeast one-hybrid assay indicated that OfSPL8 was a common upstream transcription factor of OfFT and OfBFT, suggesting the vital role of OfSPL8 in continuous flowering regulation. These results provide a novel insight into the molecular mechanism of continuous flowering.

MADS-box gene AaSEP4 promotes artemisinin biosynthesis in Artemisia annua

The plant Artemisia annua is well known for its production of artemisinin, a sesquiterpene lactone that is an effective antimalarial compound. Although remarkable progress has been made toward understanding artemisinin biosynthesis, the effect of MADS-box family transcription factors on artemisinin biosynthesis is still poorly understood. In this study, we identified a MADS transcription factor, AaSEP4, that was predominantly expressed in trichome. AaSEP4 acts as a nuclear-localized transcriptional activator activating the expression of AaGSW1 (GLANDULAR TRICHOME-SPECIFIC WRKY1). Dual-luciferase and Yeast one-hybrid assays revealed that AaSEP4 directly bound to the CArG motif in the promoter region of AaGSW1. Overexpression of AaSEP4 in A. annua significantly induced the expression of AaGSW1 and four artemisinin biosynthesis genes, including amorpha-4,11-diene synthase (ADS), cytochrome P450 monooxygenase (CYP71AV1), double-bond reductase 2 (DBR2) and aldehyde dehydrogenase 1 (ALDH1). Furthermore, the results of high-performance liquid chromatography (HPLC) showed that the artemisinin content was significantly increased in the AaSEP4-overexpressed plants. In addition, RT-qPCR results showed that AaSEP4 was induced by methyl jasmonic acid (MeJA) treatment. Taken together, these results explicitly demonstrate that AaSEP4 is a positive regulator of artemisinin biosynthesis, which can be used in the development of high-artemisinin yielding A. annua varieties.

Genome-Wide Analysis of the MADS-Box Gene Family in Holoparasitic Plants (Balanophora subcupularis and Balanophora fungosa var. globosa)

MADS-box is an important transcription factor family that is involved in the regulation of various stages of plant growth and development, especially flowering regulation and flower development. Being a holoparasitic plant, the body structure of Balanophoraceae has changed dramatically over time, and its vegetative and reproductive organs have been extensively modified, with rudimentary flower organs. Meanwhile, extraordinary gene losses have been identified in holoparasitic plants compared with autotrophs. Our study reveals that the MADS-box gene family contracted sharply in Balanophora subcupularis and Balanophora fungosa var. globosa, and some subfamilies were lost, exhibiting reduced redundancy in both. The genes that functioned in the transition from the vegetative to floral production stages suffered a significant loss, but the ABCE model genes remained intact. We further investigated genes related to flowering regulation in B. subcupularis and B. fungosa var. globosa, vernalization and autonomous ways of regulating flowering time remained comparatively integrated, while genes in photoperiod and circadian clock pathways were almost lost. Convergent gene loss in flowering regulation occurred in Balanophora and another holoparasitic plant Sapria himalayana (Rafflesiaceae). The genome-wide analysis of the MADS-box gene family in Balanophora species provides valuable information for understanding the classification, gene loss pattern, and flowering regulation mechanism of MADS-box gene family in parasitic plants.

OsMADS14 and NF-YB1 cooperate in the direct activation of OsAGPL2 and Waxy during starch synthesis in rice endosperm

Starch synthesis makes a dramatic contribution to the yield and nutritional value of cereal crops. Although several starch synthesis enzymes and related regulators have been reported, the underlying regulatory mechanisms of starch synthesis remain largely unknown. OsMADS14 is a FRUITFULL (FUL)-like MADS-box gene in rice (Oryza sativa). Here we show that two null mutations of OsMADS14 result in a shrunken and chalky grain phenotype. It is caused by obviously defective compound starch granules and a significantly reduced content of both total starch and amylose in the endosperm. Transcriptomic profiling analyses revealed that the loss-of-function of OsMADS14 leads to significantly downregulated expression of many core starch synthesis genes, including OsAGPL2 and Waxy. Both in vitro and in vivo assays demonstrate that the OsMADS14 protein directly binds to stretches of DNA with a CArG-box consensus in the putative regulatory regions of OsAGPL2 and Waxy. Protein-protein interaction experiments also suggest that OsMADS14 interacts with nuclear factor NF-YB1 to promote the transcription of OsAGPL2 and Waxy. Our study thus demonstrates that OsMADS14 plays an essential role in the synthesis of storage starch and provides novel insights into the underlying molecular mechanism that may be used to improve rice cultivars by molecular breeding.

Firming up your tomato: a natural promoter variation in a MADS-box gene is causing all-flesh tomatoes

This article comments on: Liu L, Zhang K, Bai JR, Lu J, Lu X, Hu J, Pan C, He S, Yuan J, Zhang Y, Zhang M, Guo Y, Wang X, Huang Z, Du Y, Cheng F, Li J. 2022. All-flesh fruit in tomato is controlled by reduced expression dosage of AFF through a structural variant mutation in the promoter. Journal of Experimental Botany 73, 123–138.

Genome-Wide Analysis of the MADS-Box Gene Family in Maize: Gene Structure, Evolution, and Relationships

The MADS-box gene family is one of the largest families in plants and plays an important roles in floral development. The MADS-box family includes the SRF-like domain and K-box domain. It is considered that the MADS-box gene family encodes a DNA-binding domain that is generally related to transcription factors, and plays important roles in regulating floral development. Our study identified 211 MADS-box protein sequences in the Zea mays proteome and renamed all the genes based on the gene annotations. All the 211 MADS-box protein sequences were coded by 98 expressed genes. Phylogenetic analysis of the MADS-box genes showed that all the family members were categorized into five subfamilies: MIKC-type, Mα, Mβ, Mγ, and Mδ. Gene duplications are regarded as products of several types of errors during the period of DNA replication and reconstruction; in our study all the 98 MADS-box genes contained 22 pairs of segmentally duplicated events which were distributed on 10 chromosomes. We compared expression data in different tissues from the female spikelet, silk, pericarp aleurone, ear primordium, leaf zone, vegetative meristem, internode, endosperm crown, mature pollen, embryo, root cortex, secondary root, germination kernels, primary root, root elongation zone, and root meristem. According to analysis of gene ontology pathways, we found a total of 41 pathways in which MADS-box genes in maize are involved. All the studies we conducted provided an overview of MADS-box gene family members in maize and showed multiple functions as transcription factors. The related research of MADS-box domains has provided the theoretical basis of MADS-box domains for agricultural applications.

Interaction of two MADS-box genes leads to growth phenotype divergence of all-flesh type of tomatoes

All-flesh tomato cultivars are devoid of locular gel and exhibit enhanced firmness and improved postharvest storage. Here, we show that SlMBP3 is a master regulator of locular tissue in tomato fruit and that a deletion at the gene locus underpins the All-flesh trait. Intriguingly, All-flesh varieties lack the deleterious phenotypes reported previously for SlMBP3 under-expressing lines and which preclude any potential commercial use. We resolve the causal factor for this phenotypic divergence through the discovery of a natural mutation at the SlAGL11 locus, a close homolog of SlMBP3. Misexpressing SlMBP3 impairs locular gel formation through massive transcriptomic reprogramming at initial phases of fruit development. SlMBP3 influences locule gel formation by controlling cell cycle and cell expansion genes, indicating that important components of fruit softening are determined at early pre-ripening stages. Our findings define potential breeding targets for improved texture in tomato and possibly other fleshy fruits.

Chromosome-Scale Reference Genome of Amphicarpaea edgeworthii: A New Resource for Amphicarpic Plants Research and Complex Flowering Pattern

Amphicarpaea edgeworthii, an annual twining herb, is a widely distributed species and an attractive model for studying complex flowering types and evolutionary mechanisms of species. Herein, we have generated a high-quality assembly of A. edgeworthii by using a combination of PacBio, 10× Genomics libraries, and Hi-C mapping technologies. The final 11 chromosome-level scaffolds covered 90.61% of the estimated genome (343.78Mb), which is a chromosome-scale assembled genome of an amphicarpic plant. Subsequently, we characterized the genetic diversity and population structure of A. edgeworthii species by resequencing individuals collected from their natural area of distribution. Using transcriptome profiling, we observed that specific phenotypes are regulated by a complex network of light, hormones, and MADS-box gene families. These data are beneficial for the discovery of genes that control major agronomic traits and spur genetic improvement of and functional genetic studies in legumes, as well as supply comparative genetic resources for other amphicarpic plants.

Analysis of the structure and function of the tomato Solanum lycopersicum L. MADS-box gene SlMADS5

At all stages of f lowering, a decisive role is played by the family of MADS-domain transcription factors, the combinatorial action of which is described by the ABCDE-model of f lower development. The current volume of data suggests a high conservatism of ABCDE genes in angiosperms. The E-proteins SEPALLATA are the central hub of the MADS-complexes, which determine the identity of the f loral organs. The only representative of the SEPALLATA3 clade in tomato Solanum lycopersicum L., SlMADS5, is involved in determining the identity of petals, stamens, and carpels; however, data on the functions of the gene are limited. The study was focused on the SlMADS5 functional characterization. Structural and phylogenetic analyses of SlMADS5 conf irmed its belonging to the SEP3 clade. An in silico expression analysis revealed the absence of gene transcripts in roots, leaves, and shoot apical meristem, and their presence in f lowers, fruits, and seeds at different stages of development. Two-hybrid analysis showed the ability of SlMADS5 to activate transcription of the target gene and interact with TAGL1. Transgenic plants Nicotiana tabacum L. with constitutive overexpression of SlMADS5 cDNA f lowered 2.2 times later than the control; plants formed thickened leaves, 2.5–3.0 times thicker stems, 1.5–2.7 times shortened internodes, and 1.9 times fewer f lowers and capsules than non-transgenic plants. The f lower structure did not differ from the control; however, the corolla petals changed color from light pink to magenta. Analysis of the expression of SlMADS5 and the tobacco genes NtLFY, NtAP1, NtWUS, NtAG, NtPLE, NtSEP1, NtSEP2, and NtSEP3 in leaves and apexes of transgenic and control plants showed that SlMADS5 mRNA is present only in tissues of transgenic lines. The other genes analyzed were highly expressed in the reproductive meristem of control plants. Gene transcripts were absent or were imperceptibly present in the leaves and vegetative apex of the control, as well as in the leaves and apexes of transgenic lines. The results obtained indicate the possible involvement of SlMADS5 in the regulation of f lower meristem development and the pathway of anthocyanin biosynthesis in petals.

Utilizing MIKC-type MADS-box protein SOC1 for yield potential enhancement in maize

Overexpression of Zea mays SOC gene promotes flowering, reduces plant height, and leads to no reduction in grain production per plant, suggesting enhanced yield potential, at least, through increasing planting density. MIKC-type MADS-box gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) is an integrator conserved in the plant flowering pathway. In this study, the maize SOC1 (ZmSOC1) gene was cloned and overexpressed in transgenic maize Hi-II genotype. The T₀ plants were backcrossed with nontransgenic inbred B73 to produce first generation backcross (BC₁) seeds. Phenotyping of both transgenic and null segregant (NT) BC₁ plants was conducted in three independent experiments. The BC₁ transgenic plants showed new attributes such as increased vegetative growth, accelerated flowering time, reduced overall plant height, and increased grain weight. Second generation backcross (BC₂) plants were evaluated in the field using two planting densities. Compared to BC₂ NT plants, BC₂ transgenic plants, were 12-18% shorter, flowered 5 days earlier, and showed no reduction in grain production per plant and an increase in fat, starch, and simple sugars in the grain. Transcriptome comparison in young leaves of 56-day-old BC₁ plants revealed that the overexpressed ZmSOC1 resulted in 107 differentially expressed genes. The upregulated transcription factor DNA BINDING WITH ONE FINGER 5.4 (DOF5.4) was among the genes responsible for the reduced plant height. Modulating expression of SOC1 opens a new and effective approach to promote flowering and reduce plant height, which may have potential to enhance crop yield and improve grain quality.

Multi-locus genome-wide association mapping for spike-related traits in bread wheat (Triticum aestivum L.)

BACKGROUND

Bread wheat (Triticum aestivum L.) is one of the most important cereal food crops for the global population. Spike-layer uniformity (the consistency of the spike distribution in the vertical space)-related traits (SLURTs) are quantitative and have been shown to directly affect yield potential by modifying the plant architecture. Therefore, these parameters are important breeding targets for wheat improvement. The present study is the first genome-wide association study (GWAS) targeting SLURTs in wheat. In this study, a set of 225 diverse spring wheat accessions were used for multi-locus GWAS to evaluate SLURTs, including the number of spikes per plant (NSPP), spike length (SL), number of spikelets per spike (NSPS), grain weight per spike (GWPS), lowest tiller height (LTH), spike-layer thickness (SLT), spike-layer number (SLN) and spike-layer uniformity (SLU).

RESULTS

In total, 136 significant marker trait associations (MTAs) were identified when the analysis was both performed individually and combined for two environments. Twenty-nine MTAs were detected in environment one, 48 MTAs were discovered in environment two and 59 MTAs were detected using combined data from the two environments. Altogether, 15 significant MTAs were found for five traits in one of the two environments, and four significant MTAs were detected for the two traits, LTH and SLU, in both environments i.e. E1, E2 and also in combined data from the two environments. In total, 279 candidate genes (CGs) were identified, including Chaperone DnaJ, ABC transporter-like, AP2/ERF, SWEET sugar transporter, as well as genes that have previously been associated with wheat spike development, seed development and grain yield.

CONCLUSIONS

The MTAs detected through multi-locus GWAS will be useful for improving SLURTs and thus yield in wheat production through marker-assisted and genomic selection.

Single-trait, multi-locus and multi-trait GWAS using four different models for yield traits in bread wheat

A genome-wide association study (GWAS) for 10 yield and yield component traits was conducted using an association panel comprising 225 diverse spring wheat genotypes. The panel was genotyped using 10,904 SNPs and evaluated for three years (2016-2019), which constituted three environments (E1, E2 and E3). Heritability for different traits ranged from 29.21 to 97.69%. Marker-trait associations (MTAs) were identified for each trait using data from each environment separately and also using BLUP values. Four different models were used, which included three single trait models (CMLM, FarmCPU, SUPER) and one multi-trait model (mvLMM). Hundreds of MTAs were obtained using each model, but after Bonferroni correction, only 6 MTAs for 3 traits were available using CMLM, and 21 MTAs for 4 traits were available using FarmCPU; none of the 525 MTAs obtained using SUPER could qualify after Bonferroni correction. Using BLUP, 20 MTAs were available, five of which also figured among MTAs identified for individual environments. Using mvLMM model, after Bonferroni correction, 38 multi-trait MTAs, for 15 different trait combinations were available. Epistatic interactions involving 28 pairs of MTAs were also available for seven of the 10 traits; no epistatic interactions were available for GNPS, PH, and BYPP. As many as 164 putative candidate genes (CGs) were identified using all the 50 MTAs (CMLM, 3; FarmCPU, 9; mvLMM, 6, epistasis, 21 and BLUP, 11 MTAs), which ranged from 20 (CMLM) to 66 (epistasis) CGs. In-silico expression analysis of CGs was also conducted in different tissues at different developmental stages. The information generated through the present study proved useful for developing a better understanding of the genetics of each of the 10 traits; the study also provided novel markers for marker-assisted selection (MAS) to be utilized for the development of wheat cultivars with improved agronomic traits.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01240-1.

Genome-Wide Analysis of MADS-Box Genes in Foxtail Millet (Setaria italica L.) and Functional Assessment of the Role of SiMADS51 in the Drought Stress Response

MADS-box transcription factors play vital roles in multiple biological processes in plants. At present, a comprehensive investigation into the genome-wide identification and classification of MADS-box genes in foxtail millet (Setaria italica L.) has not been reported. In this study, we identified 72 MADS-box genes in the foxtail millet genome and give an overview of the phylogeny, chromosomal location, gene structures, and potential functions of the proteins encoded by these genes. We also found that the expression of 10 MIKC-type MADS-box genes was induced by abiotic stresses (PEG-6000 and NaCl) and exogenous hormones (ABA and GA), which suggests that these genes may play important regulatory roles in response to different stresses. Further studies showed that transgenic Arabidopsis and rice (Oryza sativa L.) plants overexpressing SiMADS51 had reduced drought stress tolerance as revealed by lower survival rates and poorer growth performance under drought stress conditions, which demonstrated that SiMADS51 is a negative regulator of drought stress tolerance in plants. Moreover, expression of some stress-related genes were down-regulated in the SiMADS51-overexpressing plants. The results of our study provide an overall picture of the MADS-box gene family in foxtail millet and establish a foundation for further research on the mechanisms of action of MADS-box proteins with respect to abiotic stresses.

The Pharus latifolius genome bridges the gap of early grass evolution

The grass family (Poaceae) includes all commercial cereal crops and is a major contributor to biomass in various terrestrial ecosystems. The ancestry of all grass genomes includes a shared whole-genome duplication (WGD), named rho (ρ) WGD, but the evolutionary significance of ρ-WGD remains elusive. We sequenced the genome of Pharus latifolius, a grass species (producing a true spikelet) in the subfamily Pharoideae, a sister lineage to the core Poaceae including the (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, and Danthonioideae (PACMAD) and Bambusoideae, Oryzoideae, and Pooideae (BOP) clades. Our results indicate that the P. latifolius genome has evolved slowly relative to cereal grass genomes, as reflected by moderate rates of molecular evolution, limited chromosome rearrangements and a low rate of gene loss for duplicated genes. We show that the ρ-WGD event occurred approximately 98.2 million years ago (Ma) in a common ancestor of the Pharoideae and the PACMAD and BOP grasses. This was followed by contrasting patterns of diploidization in the Pharus and core Poaceae lineages. The presence of two FRIZZY PANICLE-like genes in P. latifolius, and duplicated MADS-box genes, support the hypothesis that the ρ-WGD may have played a role in the origin and functional diversification of the spikelet, an adaptation in grasses related directly to cereal yields. The P. latifolius genome sheds light on the origin and early evolution of grasses underpinning the biology and breeding of cereals.

K-Domain Technology: Constitutive Expression of a Blueberry Keratin-Like Domain Mimics Expression of Multiple MADS-Box Genes in Enhancing Maize Grain Yield

MADS-box genes are considered as the foundation of all agronomic traits because they play essential roles in almost every aspect of plant reproductive development. Keratin-like (K) domain is a conserved protein domain of tens of MIKC-type MADS-box genes in plants. K-domain technology constitutively expresses a K-domain to mimic expression of the K-domains of other MADS-box genes simultaneously and thus to generate new opportunities for yield enhancement, because the increased K-domains can likely prevent MADS-domain proteins from binding to target DNA. In this study, we evaluated utilizing the K-domain technology to increase maize yield. The K-domain of a blueberry's SUPPRESSOR of CONSTITUTIVE EXPRESSION OF CONSTANS 1 (VcSOC1K) has similarities to five MADS-box genes in maize. Transgenic maize plants expressing the VcSOC1K showed 13-100% of more grain per plant than the nontransgenic plants in all five experiments conducted under different experimental conditions. Transcriptome comparisons revealed 982 differentially expressed genes (DEGs) in the leaves from 83-day old plants, supporting that the K-domain technology were powerful and multiple functional. The results demonstrated that constitutive expression of the VcSOC1K was very effective to enhance maize grain production. With the potential of mimicking the K-domains of multiple MADS-box genes, the K-domain technology opens a new approach to increase crop yield.

Cotton architecture: examining the roles of SINGLE FLOWER TRUSS and SELF-PRUNING in regulating growth habits of a woody perennial crop

By specifying patterns of determinate and indeterminate growth, FLOWERING LOCUS T/SINGLE FLOWER TRUSS (SFT) and TERMINAL FLOWER 1/SELF-PRUNING (SP) regulate plant architecture. Though well characterized in Arabidopsis, the impacts of these genes on the architectures of diverse crops cultivated in different environments, and their potential to enhance crop productivity and management, are less well addressed. Cotton (Gossypium spp.) is naturally a short-day photoperiodic perennial that is now grown primarily as a day-neutral, annual row crop. Different environments and cultivation practices favor specific growth habits to optimize yield, and in cotton, especially in regions that rely heavily on mechanized harvest, the trend has been to more determinate varieties. Identifying and functionally characterizing SFT and SP homologs in cotton uncovered new aspects of how ratios of indeterminate and determinate growth are balanced, and unraveling their genetic networks emphasized how broadly these gene products affect cotton growth habits.

Hypothesis-based food, feed, and environmental safety assessment of GM crops: A case study using maize event DP-202216-6

Event DP-2Ø2216-6 (referred to as DP202216 maize) was genetically modified to increase and extend the expression of the introduced zmm28 gene relative to endogenous zmm28 gene expression, resulting in plants with enhanced grain yield potential. The zmm28 gene expresses the ZMM28 protein, a MADS-box transcription factor. The safety assessment of DP202216 maize included an assessment of the potential hazard of the ZMM28 protein, as well as an assessment of potential unintended effects of the genetic insertion on agronomics, composition, and nutrition. The history of safe use (HOSU) of the ZMM28 protein was evaluated and a bioinformatics approach was used to compare the deduced amino acid sequence of the ZMM28 protein to databases of known allergens and toxins. Based on HOSU and the bioinformatics assessment, the ZMM28 protein was determined to be unlikely to be either allergenic or toxic to humans. The composition of DP202216 maize forage and grain was comparable to non-modified forage and grain, with no unintended effects on nutrition or food and feed safety. Additionally, feeding studies with broiler chickens and rats demonstrated a low likelihood of unintentional alterations in nutrition and low potential for adverse effects. Furthermore, the agronomics observed for DP202216 maize and non-modified maize were comparable, indicating that the likelihood of increased weediness or invasiveness of DP202216 maize in the environment is low. This comprehensive review serves as a reference for regulatory agencies and decision-makers in countries where authorization of DP202216 maize will be pursued, and for others interested in food, feed, and environmental safety.

Overexpression of SlMBP22 in Tomato Affects Plant Growth and Enhances Tolerance to Drought Stress

MADS-box transcription factors play crucial and diverse roles in plant growth and development, and the responses to biotic and abiotic stresses. However, the implementation of MADS-box transcription factors in regulating plant architecture and stress responses has not been fully explored in tomato. Here, we found that a novel MADS-box transcription factor, SlMBP22, participated in the control of agronomical traits, tolerance to abiotic stress, and regulation of auxin and gibberellin signalling. Transgenic plants overexpressing SlMBP22 (SlMBP22-OE) displayed pleiotropic phenotypes, including reduced plant height and leaf size, by affecting auxin and/or gibberellin signalling. SlMBP22 was induced by dehydration treatment, and SlMBP22-OE plants were more tolerant to drought stress than wild-type (WT). Furthermore, SlMBP22 overexpression plants accumulated more chlorophyll, starch and soluble sugar than WT, indicating that the darker green leaves might be attributed to increased chlorophyll levels in the transgenic plants. RNA-Seq results showed that the transcript levels of a series of genes related to chloroplast development, chlorophyll metabolism, starch and sucrose metabolism, hormone signalling, and stress responses were altered. Collectively, our data demonstrate that SlMBP22 plays an important role in both regulating tomato growth and resisting drought stress.

Characteristics of banana B genome MADS-box family demonstrate their roles in fruit development, ripening, and stress

MADS-box genes are critical regulators of growth and development in flowering plants. Sequencing of the Musa balbisiana (B) genome has provided a platform for the systematic analysis of the MADS-box gene family in the important banana ancestor Musa balbisiana. Seventy-seven MADS-box genes, including 18 type I and 59 type II, were strictly identified from the banana (Pisang Klutuk Wulung, PKW, 2n = 2x = 22) B genome. These genes have been preferentially placed on the banana B genome. Evolutionary analysis suggested that M. balbisiana MCM1-AGAMOUS-DEFICIENS-SRF (MbMADS) might be organized into the MIKC^c, MIKC*, Mα, Mβ, and Mγ groups according to the phylogeny. MIKC^c was then further categorized into 10 subfamilies according to conserved motif and gene structure analyses. The well-defined MADS-box genes highlight gene birth and death in banana. MbMADSes originated from the same ancestor as MaMADSes. Transcriptome analysis in cultivated banana (ABB) revealed that MbMADSes were conserved and differentially expressed in several organs, in various fruit developing and ripening stages, and in stress treatments, indicating the participation of these genes in fruit development, ripening, and stress responses. Of note, SEP/AGL2 and AG, as well as other several type II MADS-box genes, including the STMADS11 and TM3/SOC1 subfamilies, indicated elevated expression throughout banana fruit development, ripening, and stress treatments, indicating their new parts in controlling fruit development and ripening. According to the co-expression network analysis, MbMADS75 interacted with bZIP and seven other transcription factors to perform its function. This systematic analysis reveals fruit development, ripening, and stress candidate MbMADSes genes for additional functional studies in plants, improving our understanding of the transcriptional regulation of MbMADSes genes and providing a base for genetic modification of MADS-mediated fruit development, ripening, and stress.

Genome-wide identification of MADS-box gene family in sacred lotus (Nelumbo nucifera) identifies a SEPALLATA homolog gene involved in floral development

BACKGROUND

Sacred lotus (Nelumbo nucifera) is a vital perennial aquatic ornamental plant. Its flower shape determines the horticultural and ornamental values. However, the mechanisms underlying lotus flower development are still elusive. MADS-box transcription factors are crucial in various features of plant development, especially in floral organogenesis and specification. It is still unknown how the MADS-box transcription factors regulate the floral organogenesis in lotus.

RESULTS

To obtain a comprehensive insight into the functions of MADS-box genes in sacred lotus flower development, we systematically characterized members of this gene family based on the available genome information. A total of 44 MADS-box genes were identified, of which 16 type I and 28 type II genes were categorized based on the phylogenetic analysis. Furthermore, the structure of MADS-box genes and their expressional patterns were also systematically analyzed. Additionally, subcellular localization analysis showed that they are mainly localized in the nucleus, of which a SEPALLATA3 (SEP3) homolog NnMADS14 was proven to be involved in the floral organogenesis.

CONCLUSION

These results provide some fundamental information about the MADS-box gene family and their functions, which might be helpful in not only understanding the mechanisms of floral organogenesis but also breeding of high ornamental value cultivars in lotus.

First approach to pod dehiscence in faba bean: genetic and histological analyses

Pod dehiscence causes important yield losses in cultivated crops and therefore has been a key trait strongly selected against in crop domestication. In spite of the growing knowledge on the genetic basis of dehiscence in different crops, no information is available so far for faba bean. Here we conduct the first comprehensive study for faba bean pod dehiscence by combining, linkage mapping, comparative genomics, QTL analysis and histological examination of mature pods. Mapping of dehiscence-related genes revealed conservation of syntenic blocks among different legumes. Three QTLs were identified in faba bean chromosomes II, IV and VI, although none of them was stable across years. Histological analysis supports the convergent phenotypic evolution previously reported in cereals and related legume species but revealed a more complex pattern in faba bean. Contrary to common bean and soybean, the faba bean dehiscence zone appears to show functional equivalence to that described in crucifers. The lignified wall fiber layer, which is absent in the paucijuga primitive line Vf27, or less lignified and vacuolated in other dehiscent lines, appears to act as the major force triggering pod dehiscence in this species. While our findings, provide new insight into the mechanisms underlying faba bean dehiscence, full understanding of the molecular bases will require further studies combining precise phenotyping with genomic analysis.