Plants flower in response to environmental signals. These signals change the shape and developmental identity of the shoot apical meristem (SAM), causing it to form flowers and inflorescences. We show that the increases in SAM width and height during floral transition correlate with changes in size of the central zone (CZ), defined by CLAVATA3 expression, and involve a transient increase in the height of the organizing center (OC), defined by WUSCHEL expression. The APETALA2 (AP2) transcription factor is required for the rapid increases in SAM height and width, by maintaining the width of the OC and increasing the height and width of the CZ. AP2 expression is repressed in the SAM at the end of floral transition, and extending the duration of its expression increases SAM width. Transcriptional repression by SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) represents one of the mechanisms reducing AP2 expression during floral transition. Moreover, AP2 represses SOC1 transcription, and we find that reciprocal repression of SOC1 and AP2 contributes to synchronizing precise changes in meristem shape with floral transition.

BACKGROUND: In Angiosperms, the continuation of plant species is intricately dependent on the funiculus multifaceted role in nutrient transport, mechanical support, and dehiscence of seeds. SEEDSTICK (STK) is a MADS-box transcription factor involved in seed size and abscission, and one of the few genes identified as affecting funiculus growth. Given the importance of the funiculus to a correct seed development, allied with previous phenotypic observations of stk mutants, we performed a transcriptomic analysis of stk funiculi from floral stage 17, using RNA-sequencing, to infer on the deregulated networks of genes.
RESULTS: The generated dataset of differentially expressed genes was enriched with cell wall biogenesis, cell cycle, sugar metabolism and transport terms, all in accordance with stk phenotype observed in funiculi from floral stage 17. We selected eight differentially expressed genes for transcriptome validation using qPCR and/or promoter reporter lines. Those genes were involved with abscission, seed development or novel functions in stk funiculus, such as hormones/secondary metabolites transport.
CONCLUSIONS: Overall, the analysis performed in this study allowed delving into the STK-network established in Arabidopsis funiculus, fulfilling a literature gap. Simultaneously, our findings reinforced the reliability of the transcriptome, making it a valuable resource for candidate genes selection for functional genetic studies in the funiculus. This will enhance our understanding on the regulatory network controlled by STK, on the role of the funiculus and how seed development may be affected by them.

Evolution of unisexual flowers involves extreme changes in floral development. Spinach is one of the species to discern the formation and evolution of dioecy. MADS-box gene family is involved in regulation of floral organ identity and development and in many other plant developmental processes. However, there is no systematic analysis of MADS-box family genes in spinach. A comprehensive genome-wide analysis and transcriptome profiling of MADS-box genes were undertaken to understand their involvement in unisexual flower development at different stages in spinach. In total, 54 MADS-box genes found to be unevenly located across 6 chromosomes and can be divided into type I and type II genes. Twenty type I MADS-box genes are subdivided into Mα, Mβ and Mγ subgroups. While thirty-four type II SoMADSs consist of 3 MIKC*, and 31 MIKCC -type genes including sixteen floral homeotic MADS-box genes that are orthologous to the proposed Arabidopsis ABCDE model of floral organ identity determination, were identified in spinach. Gene structure, motif distribution, physiochemical properties, gene duplication and collinearity analyses for these genes are performed in detail. Promoters of both types of SoMADS genes contain mainly MeJA and ABA response elements. Expression profiling indicated that MIKCc genes exhibited more dynamic and intricate expression patterns compared to M-type genes and the majority of type-II genes AP1, SVP, and SOC1 sub-groups showed female flower-biased expression profiles, suggesting their role in carpel development, while PI showed male-biased expression throughout flower developmental stages, suggesting their role in stamen development. These results provide genomic resources and insights into spinach dioecious flower development and expedite spinach improvement.

Most of the studied MADS box members are linked to flowering and fruit traits. However, higher volumes of studies on type II of the two types so far suggest that the florigenic effect of the gene members could just be the tip of the iceberg. In the current study, we used a systematic approach to obtain a general overview of the MADS box members\' cross-trait and multifactor associations, and their pleiotropic potentials, based on a manually curated local reference database. While doing so, we screened for the co-occurrence of terms of interest within the title or abstract of each reference, with a threshold of three hits. The analysis results showed that our approach can retrieve multi-faceted information on the subject of study (MADS box gene members in the current case), which could otherwise have been skewed depending on the authors\' expertise and/or volume of the literature reference base. Overall, our study discusses the roles of MADS box members in association with plant organs and trait-linked factors among plant species. Our assessment showed that plants with most of the MADS box member studies included tomato, apple, and rice after Arabidopsis. Furthermore, based on the degree of their multi-trait associations, FLC, SVP, and SOC1 are suggested to have relatively higher pleiotropic potential among others in plant growth, development, and flowering processes. The approach devised in this study is expected to be applicable for a basic understanding of any study subject of interest, regardless of the depth of prior knowledge.

In wheat, the transition of the inflorescence meristem to a terminal spikelet (IM→TS) determines the spikelet number per spike (SNS), an important yield component. In this study, we demonstrate that the plant-specific transcription factor LEAFY (LFY) physically and genetically interacts with WHEAT ORTHOLOG OF APO1 (WAPO1) to regulate SNS and floret development. Loss-of-function mutations in either or both genes result in significant and similar reductions in SNS, as a result of a reduction in the rate of spikelet meristem formation per day. SNS is also modulated by significant genetic interactions between LFY and the SQUAMOSA MADS-box genes VRN1 and FUL2, which promote the IM→TS transition. Single-molecule fluorescence in situ hybridization revealed a downregulation of LFY and upregulation of the SQUAMOSA MADS-box genes in the distal part of the developing spike during the IM→TS transition, supporting their opposite roles in the regulation of SNS in wheat. Concurrently, the overlap of LFY and WAPO1 transcription domains in the developing spikelets contributes to normal floret development. Understanding the genetic network regulating SNS is a necessary first step to engineer this important agronomic trait.

High temperature (HT) is an environmental factor that considerably affects plant physiology, development, crop yield, and economic value. HT can cause diseases and early bolting of leaf lettuce, thereby reducing the yield and quality of leaf lettuce. Herein, we used two leaf lettuce (Lactuca sativa L.) cultivars (bolting-resistant \'S24\' and bolting-sensitive \'S39\') to investigate the key factors and molecular mechanism impacting bolting. We found that 14 MADS-box genes implicated in bolting and flowering, LsMADS54 (also referred to as L. sativa FRUITFULL, LsFUL), was significantly up-regulated 1000 times after 5-d HT treatment and that HT-induced up-regulation of LsFUL was higher in bolting-sensitive than in resistant cultivars. The overexpression lines of LsFUL exhibited an earlier bolting time than that in the non-transformed \'S39\'(CK). However, the RNA interference, and CRISPR-Cas9-mediated knockout lines of LsFUL exhibited a later bolting time than that in CK. In addition, we found that L. sativa SUPPRESSORS OF MEC-8 AND UNC-52 PROTEIN 2 (LsSMU2) and L. sativa CONSTANS-LIKE PROTEIN 5 (LsCOL5) interact with LsFUL, and these interactions could stimulate or prevent bolting. We observed that elevated temperature stimulated the abundance of LsSMU2 in the stem, which collaborated with LsFUL to accelerate bolting. Conversely, room temperature (RT) condition led to relatively more stable LsCOL5, which worked with LsFUL to postpone bolting. In summary, our findings demonstrate a molecular regulatory module of LsSMU2-LsFUL associated with HT-induced premature bolting, which serves as a reference for understanding HT-induced premature bolting phenomenon in leaf lettuce.

A novel MADS-box transcription factor from Pinus radiata D. Don was characterized. PrMADS11 encodes a protein of 165 amino acids for a MADS-box transcription factor belonging to group II, related to the MIKC protein structure. PrMADS11 was differentially expressed in the stems of pine trees in response to 45° inclination at early times (1 h). Arabidopsis thaliana was stably transformed with a 35S::PrMADS11 construct in an effort to identify the putative targets of PrMADS11. A massive transcriptome analysis revealed 947 differentially expressed genes: 498 genes were up-regulated, and 449 genes were down-regulated due to the over-expression of PrMADS11. The gene ontology analysis highlighted a cell wall remodeling function among the differentially expressed genes, suggesting the active participation of cell wall modification required during the response to vertical stem loss. In addition, the phenylpropanoid pathway was also indicated as a PrMADS11 target, displaying a marked increment in the expression of the genes driven to the biosynthesis of monolignols. The EMSA assays confirmed that PrMADS11 interacts with CArG-box sequences. This TF modulates the gene expression of several molecular pathways, including other TFs, as well as the genes involved in cell wall remodeling. The increment in the lignin content and the genes involved in cell wall dynamics could be an indication of the key role of PrMADS11 in the response to trunk inclination.

The development of floral organs, crucial for the establishment of floral symmetry and morphology in higher plants, is regulated by MADS-box genes. In sunflower, the capitulum is comprised of ray and disc florets with various floral organs. In the sunflower long petal mutant (lpm), the abnormal disc (ray-like) floret possesses prolongated petals and degenerated stamens, resulting in a transformation from zygomorphic to actinomorphic symmetry. In this study, we investigated the effect of MADS-box genes on floral organs, particularly on petals, using WT and lpm plants as materials. Based on our RNA-seq data, 29 MADS-box candidate genes were identified, and their roles on floral organ development, especially in petals, were explored, by analyzing the expression levels in various tissues in WT and lpm plants through RNA-sequencing and qPCR. The results suggested that HaMADS3, HaMADS7, and HaMADS8 could regulate petal development in sunflower. High levels of HaMADS3 that relieved the inhibition of cell proliferation, together with low levels of HaMADS7 and HaMADS8, promoted petal prolongation and maintained the morphology of ray florets. In contrast, low levels of HaMADS3 and high levels of HaMADS7 and HaMADS8 repressed petal extension and maintained the morphology of disc florets. Their coordination may contribute to the differentiation of disc and ray florets in sunflower and maintain the balance between attracting pollinators and producing offspring. Meanwhile, Pearson correlation analysis between petal length and expression levels of MADS-box genes further indicated their involvement in petal prolongation. Additionally, the analysis of cis-acting elements indicated that these three MADS-box genes may regulate petal development and floral symmetry establishment by regulating the expression activity of HaCYC2c. Our findings can provide some new understanding of the molecular regulatory network of petal development and floral morphology formation, as well as the differentiation of disc and ray florets in sunflower.

BACKGROUND: The MADS-box gene family is widely distributed in the plant kingdom, and its members typically encoding transcription factors to regulate various aspects of plant growth and development. In particular, the MIKC-type MADS-box genes play a crucial role in the determination of floral organ development and identity recognition. As a type of androdioecy plant, Chionanthus retusus have unique gender differentiation. Manifested as male individuals with only male flowers and female individuals with only bisexual flowers. However, due to the lack of reference genome information, the characteristics of MIKC-type MADS-box genes in C. retusus and its role in gender differentiation of C. retusus remain largely unknown. Therefore, it is necessary to identify and characterize the MADS-box gene family within the genome of the C. retusus.
RESULTS: In this study, we performed a genome-wide identification and analysis of MIKC-type MADS-box genes in C. retusus (2n = 2x = 46), utilizing the latest reference genome, and studied its expression pattern in individuals of different genders. As a result, we identified a total of 61 MIKC-type MADS-box genes in C. retusus. 61 MIKC-type MADS-box genes can be divided into 12 subfamilies and distributed on 18 chromosomes. Genome collinearity analysis revealed their conservation in evolution, while gene structure, domains and motif analysis indicated their conservation in structure. Finally, based on their expression patterns in floral organs of different sexes, we have identified that CrMADS45 and CrMADS60 may potentially be involved in the gender differentiation of C. retusus.
CONCLUSIONS: Our studies have provided a general understanding of the conservation and characteristics of the MIKC-type MADS-box genes family in C. retusus. And it has been demonstrated that members of the AG subfamily, CrMADS45 and CrMADS60, may play important roles in the gender differentiation of C. retusus. This provides a reference for future breeding efforts to improve flower types in C. retusus and further investigate the role of MIKC-type MADS-box genes in gender differentiation.

The plant MADS-box transcription factor family is a major regulator of plant flower development and reproduction, and the AGAMOUS-LIKE11/SEEDSTICK (AGL11/STK) subfamily plays conserved functions in the seed development of flowering plants. Camellia japonica is a world-famous ornamental flower, and its seed kernels are rich in highly valuable fatty acids. Seed abortion has been found to be common in C. japonica, but little is known about how it is regulated during seed development. In this study, we performed a genome-wide analysis of the MADS-box gene the in C. japonica genome and identified 126 MADS-box genes. Through gene expression profiling in various tissue types, we revealed the C/D-class MADS-box genes were preferentially expressed in seed-related tissues. We identified the AGL11/STK-like gene, CjSTK, and showed that it contained a typical STK motif and exclusively expressed during seed development. We found a significant increase in the CjSTK expression level in aborted seeds compared with normally developing seeds. Furthermore, overexpression of CjSTK in Arabidopsis thaliana caused shorter pods and smaller seeds. Taken together, we concluded that the fine regulation of the CjSTK expression at different stages of seed development is critical for ovule formation and seed abortion in C. japonica. The present study provides evidence revealing the regulation of seed development in Camellia.