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Temperature-dependent alternative splicing of FLOWERING LOCUS M ( FLM ) results in two protein products, FLM-β and FLM-δ, that regulate the onset of flowering in Arabidopsis ; at cooler temperatures FLM-β represses flowering, whereas at higher temperatures, the plant preferentially produces FLM-δ, which promotes flowering. Flowering when the temperature is right The transition to flowering is a critical event in the life cycle of a flowering plant and it needs to be timed precisely to ensure reproductive success. Here Markus Schmid and colleagues study the regulation of flowering in response to changes in ambient temperature. They show that temperature-dependent alternative splicing of FLOWERING LOCUS M ( FLM ) yields two protein products, FLM-β and FLM-δ, that regulate flowering in opposite ways. At cooler temperatures FLM-β represses flowering, whereas at higher temperatures the plant preferentially produces FLM-δ to promote flowering. Hence, temperature-dependent alternative pre-mRNA splicing controls the onset of flowering. The appropriate timing of flowering is crucial for plant reproductive success. It is therefore not surprising that intricate genetic networks have evolved to perceive and integrate both endogenous and environmental signals, such as carbohydrate and hormonal status, photoperiod and temperature 1 , 2 . In contrast to our detailed understanding of the vernalization pathway, little is known about how flowering time is controlled in response to changes in the ambient growth temperature. In Arabidopsis thaliana , the MADS-box transcription factor genes FLOWERING LOCUS M ( FLM ) and SHORT VEGETATIVE PHASE ( SVP ) have key roles in this process 3 , 4 . FLM is subject to temperature-dependent alternative splicing 3 . Here we report that the two main FLM protein splice variants, FLM-β and FLM-δ, compete for interaction with the floral repressor SVP. The SVP–FLM-β complex is predominately formed at low temperatures and prevents precocious flowering. By contrast, the competing SVP–FLM-δ complex is impaired in DNA binding and acts as a dominant-negative activator of flowering at higher temperatures. Our results show a new mechanism that controls the timing of the floral transition in response to changes in ambient temperature. A better understanding of how temperature controls the molecular mechanisms of flowering will be important to cope with current changes in global climate 5 , 6 .

How florigen says it with flowers Florigen, a plant hormone that translocates from leaves to the shoot apex to induce flowering, is encoded by the FLOWERING LOCUS T ( FT ) gene. The detailed molecular mechanism for florigen action and the identity of its receptors remained unknown. Ko Shimamoto and colleagues show that in rice, florigen binds to 14-3-3 proteins, a type of regulatory molecule present in all eukaryotic cells, and to the transcription factor OsFD1. The crystal structure of the resulting florigen activation complex (FAC) has been determined, providing a mechanistic basis for florigen function in flowering. This work offers clues for improving agriculturally important traits by manipulating florigen and its regulators. ‘Florigen’ was proposed 75 years ago 1 to be synthesized in the leaf and transported to the shoot apex, where it induces flowering. Only recently have genetic and biochemical studies established that florigen is encoded by FLOWERING LOCUS T ( FT ), a gene that is universally conserved in higher plants 2 , 3 , 4 . Nonetheless, the exact function of florigen during floral induction remains poorly understood and receptors for florigen have not been identified. Here we show that the rice FT homologue Hd3a 5 interacts with 14-3-3 proteins in the apical cells of shoots, yielding a complex that translocates to the nucleus and binds to the Oryza sativa (Os)FD1 transcription factor, a rice homologue of Arabidopsis thaliana FD. The resultant ternary ‘florigen activation complex’ (FAC) induces transcription of OsMADS15 , a homologue of A. thaliana APETALA1 ( AP1 ), which leads to flowering. We have determined the 2.4 Å crystal structure of rice FAC, which provides a mechanistic basis for florigen function in flowering. Our results indicate that 14-3-3 proteins act as intracellular receptors for florigen in shoot apical cells, and offer new approaches to manipulate flowering in various crops and trees.

Background In animals, pioneer transcription factors (TFs) have long been known to be crucial molecular players in programming cell fate. However, in plants much less is known about this functional class of TFs and how they mechanistically alter local chromatin architecture in order to reprogramme gene regulation to orchestrate cell fate changes. Results Here, we provide evidence that APETALA1 (AP1) functions as a pioneer TF in Arabidopsis thaliana , facilitated by tetramerisation. Using an integrated combination of multi-omics and high-resolution imaging approaches on both wild-type and AP1 mutant transgenic plants, we show that tetramerisation assists AP1 in providing access to, and enhancing the binding of AP1 to, closed chromatin in vivo . This, in turn, allows for a switching of the chromatin state from closed to open to ensure access to target DNA sequences needed for organ specification. Conclusions These novel insights provide a mechanistic basis for how AP1 functions as a pioneer factor to reprogramme stem cells towards a “floral ground state”, increasing our understanding of how MADS-domain TFs function as combinatorial units during early Arabidopsis thaliana reproductive development.

Key messageA novel MADS-box member SiMADS34 is essential for regulating inflorescence architecture and grain yield in Setaria italica.MADS-box transcription factors participate in regulating various developmental processes in plants. Inflorescence architecture is one of the most important agronomic traits and is closely associated with grain yield in most staple crops. Here, we isolated a panicle development mutant simads34 from a foxtail millet (Setaria italica (L.) P. Beauv.) EMS mutant library. The mutant showed significantly altered inflorescence architecture and decreased grain yield. Investigation of agronomic traits revealed increased panicle width by 16.8%, primary branch length by 10%, and number of primary branches by 30.9%, but reduced panicle length by 25.2%, and grain weight by 25.5% in simads34 compared with wild-type plants. Genetic analysis of a simads34 × SSR41 F2 population indicated that the simads34 phenotype was controlled by a recessive gene. Map-based cloning and bulked-segregant analysis sequencing demonstrated that a single G-to-A transition in the fifth intron of SiMADS34 in the mutant led to an alternative splicing event and caused an early termination codon in this causal gene. SiMADS34 mRNA was expressed in all of the tissues tested, with high expression levels at the heading and panicle development stages. Subcellular localization analysis showed that simads34 predominantly accumulated in the nucleus. Transcriptome sequencing identified 241 differentially expressed genes related to inflorescence development, cell expansion, cell division, meristem growth and peroxide stress in simads34. Notably, an SPL14–MADS34–RCN pathway was validated through both RNA-seq and qPCR tests, indicating the putative molecular mechanisms regulating inflorescence development by SiMADS34. Our study identified a novel MADS-box member in foxtail millet and provided a useful genetic resource for inflorescence architecture and grain yield research.

Background Paeonia section Moutan DC. is a significant perennial subshrub, the ornamental value of which heavily depends on the type of flower it possesses. MADS-box transcription factors have a particular impact on the intricate process of floral organ development and differentiation. The release of the whole-genome data from Paeonia ostii now allows us to conduct a thorough investigation of the tree peony MADS-box gene family. Results In this study, we identified 110 MADS-box genes in Paeonia ostii that were classified into 5 subgroups. Gene structure, domain and motif analyses revealed the conservation of the structure of these subgroups. Analysis of the cis -acting elements revealed that the 110 PoMADS genes contained different kinds of hormones and stress-related cis -acting elements in their promoter regions. Quantitative real-time PCR analysis was employed to validate the expression patterns of some PoMADS genes related to floral organ development. Genome collinearity analysis with Arabidopsis and grape revealed the conservation of PoMADS genes during evolution. A total of 857 SSRs were identified by analysing the genome sequences of identified genes. We additionally created protein‒protein interaction networks for PoMADS proteins and analysed proteins that could interact among PoMADSs in Arabidopsis thaliana and grape. Conclusion These findings offer fundamental insights for understanding the function of the MADS-box gene family, which can aid in the selection and breeding of tree peony varieties with high ornamental value in addition to supporting the understanding of the process of tree peony floral organogenesis.

Diffuse large B cell lymphomas can arise from dysregulation of BCL6 expression. Dalla-Favera and colleagues show that the transcription factor MEF2B regulates BCL6 and is commonly associated with the generation of such lymphomas. MEF2B encodes a transcriptional activator and is mutated in ∼11% of diffuse large B cell lymphomas (DLBCLs) and ∼12% of follicular lymphomas (FLs). Here we found that MEF2B directly activated the transcription of the proto-oncogene BCL6 in normal germinal-center (GC) B cells and was required for DLBCL proliferation. Mutation of MEF2B resulted in enhanced transcriptional activity of MEF2B either through disruption of its interaction with the corepressor CABIN1 or by rendering it insensitive to inhibitory signaling events mediated by phosphorylation and sumoylation. Consequently, the transcriptional activity of Bcl-6 was deregulated in DLBCLs with MEF2B mutations. Thus, somatic mutations of MEF2B may contribute to lymphomagenesis by deregulating BCL6 expression, and MEF2B may represent an alternative target for blocking Bcl-6 activity in DLBCLs.

Background The MADS-box gene family possesses significant potential to improve crop production under harsh conditions by regulating growth, development, and the expression of floral organs. The grass pea (Lathyrus sativus), a crop grown predominantly in arid and semi-arid regions, could benefit greatly from the functions of MADS-box genes, which are not yet well characterized in this promising plant. Results In this study, a comprehensive analysis of all MADS-box genes in grass pea was performed at both the genomic and transcriptomic levels. A total of 46 genes were identified and classified based on their MADS-box domains. A comparative phylogenetic analysis with apple, Arabidopsis, and rice categorized the grass pea genes into 31 type I genes (M , M , M ) and 15 type II genes (MIKCc, MIKC*). Annotation analysis revealed variations in the intron-exon structures of the genes, with most type I genes being intronless. Ten distinct conserved motifs were identified across the genes. Structural analysis revealed the presence of MEF2-like and SRF-TF domains in the grass pea proteins. Protein-protein interaction analysis revealed extensive interactions among type II MADS-box genes, while enrichment analysis showed their involvement in various aspects of plant life, particularly floral organ development. Examination of the cis-elements in the promoter regions of the genes revealed up to 76 potential cis-elements, which were categorized into four groups based on their putative role in transcriptional regulation. RNA-seq was used to profile gene expression under different conditions to gain insights into their potential functional significance. Quantitative PCR (qPCR) analysis validated the expression levels of eight selected genes (LSMADS_D1, LSMADS_R5, LSMADS_R7, LSMADS_R9, LSMADS_D11, LSMADS_D13, LSMADS_R13, and LSMADS_D29) under salt stress conditions and confirmed their involvement in stress responses. Conclusion This study represents the first genome-wide exploration of the MADS-box gene family in grass pea. Our results provide valuable insights that could improve our understanding of the plant’s genomics, contribute to strengthening its resilience to challenging conditions, and help position it as an important crop in arid regions.

In plants, MADS domain transcription factors act as central regulators of diverse developmental pathways. In Arabidopsis thaliana, one of the most central members of this family is SEPALLATA3 ( SEP3), which is involved in many aspects of plant reproduction, including floralmeristem and floral organ development. SEP3 has been shown to form homo and heterooligomeric complexes with other MADS domain transcription factors through its intervening ( I) and keratin-like ( K) domains. SEP3 function depends on its ability to form specific protein-protein complexes; however, the atomic level determinants of oligomerization are poorly understood. Here, we report the 2.5 angstrom crystal structure of a small portion of the intervening and the complete keratin-like domain of SEP3. The domains form two amphipathic alpha helices separated by a rigid kink, which prevents intramolecular association and presents separate dimerization and tetramerization interfaces comprising predominantly hydrophobic patches. Mutations to the tetramerization interface demonstrate the importance of highly conserved hydrophobic residues for tetramer stability. Atomic force microscopy was used to show SEP3-DNA interactions and the role of oligomerization in DNA binding and conformation. Based on these data, the oligomerization patterns of the larger family of MADS domain transcription factors can be predicted and manipulated based on the primary sequence.

Rubber dandelion (Taraxacum kok-saghyz Rodin, TKS), also referred to as Russian dandelion, is one of the most promising natural rubber (NR)-producing plants that produce high-quality NR comparable to that from the Pará rubber tree (Hevea brasiliensis, Hb), currently the only commercial source. It needs further breeding to improve the agricultural traits. However, little has been known about the genetic mechanisms underlying the regulation of floral induction and flower development in TKS, an important trait that remains to be improved for commercial production. The MADS-box gene AGAMOUS-LIKE 24 (AGL24) plays important roles in floral induction and flower development. As the first step in understanding its roles in TKS, this study isolated and characterized the AGL24-homologous gene TkAGL24 in TKS. The TkAGL24 gene had a 705 bp coding sequence (CDS) that encoded a protein of 234 amino acids containing the conserved classic MADS-box type II domain and K-box domain, sharing 55.32% protein sequence identity with the AtAGL24 protein from Arabidopsis. TkAGL24 was highly expressed in leaf, latex, root, and peduncle but rarely or not in mature flower. The TkAGL24 protein was located in the nucleus and cytoplasm and did not have transcription activation activity in yeast cells. The overexpression of TkAGL24 in Arabidopsis could promote flowering and cause the abnormal development of flowers, similar to other AGL24-homologous genes from other species. Furthermore, the overexpression of TkAGL24 in TKS also affected the development of ligulate flowers. These results suggested that the cloned TkAGL24 gene is functional and may play important roles in floral induction and flower development in TKS, providing an insight into the possibility for the further studies of its roles and application to breeding.

Abscission is the mechanism by which plants disconnect unfertilized flowers, ripe fruits, senescent or diseased organs from the plant. In tomato, pedicel abscission is an important agronomic factor that controls yield and post-harvest fruit quality. Two non-allelic mutations, jointless ( j ) and jointless-2 ( j-2 ), controlling pedicel abscission zone formation have been documented but only j-2 has been extensively used in breeding. J was shown to encode a MADS-box protein. Using a combination of physical mapping and gene expression analysis we identified a positional candidate, Solyc12g038510 , associated with j-2 phenotype. Targeted knockout of Solyc12g038510 , using CRISPR/Cas9 system, validated our hypothesis. Solyc12g038510 encodes the MADS-box protein SlMBP21. Molecular analysis of j-2 natural variation revealed two independent loss-of-function mutants. The first results of an insertion of a Rider retrotransposable element. The second results of a stop codon mutation that leads to a truncated protein form. To bring new insights into the role of J and J-2 in abscission zone formation, we phenotyped the single and the double mutants and the engineered alleles. We showed that J is epistatic to J-2 and that the branched inflorescences and the leafy sepals observed in accessions harboring j-2 alleles are likely the consequences of linkage drags.