Overexpression of four MiTFL1 genes from mango delays the flowering time in transgenic Arabidopsis

Background TERMINAL FLOWER 1 (TFL1) belongs to the phosphatidylethanolamine-binding protein (PEBP) family, which is involved in inflorescence meristem development and represses flowering in several plant species. In the present study, four TFL1 genes were cloned from the mango (Mangifera indica L.) variety ‘SiJiMi’ and named MiTFL1-1, MiTFL1-2, MiTFL1-3 and MiTFL1-4. Results Sequence analysis showed that the encoded MiTFL1 proteins contained a conserved PEBP domain and belonged to the TFL1 group. Expression analysis showed that the MiTFL1 genes were expressed in not only vegetative organs but also reproductive organs and that the expression levels were related to floral development. Overexpression of the four MiTFL1 genes delayed flowering in transgenic Arabidopsis. Additionally, MiTFL1-1 and MiTFL1-3 changed the flower morphology in some transgenic plants. Yeast two-hybrid (Y2H) analysis showed that several stress-related proteins interacted with MiTFL1 proteins. Conclusions The four MiTFL1 genes exhibited a similar expression pattern, and overexpression in Arabidopsis resulted in delayed flowering. Additionally, MiTFL1-1 and MiTFL1-3 overexpression affected floral organ development. Furthermore, the MiTFL1 proteins could interact with bHLH and 14-3-3 proteins. These results indicate that the MiTFL1 genes may play an important role in the flowering process in mango.

LEAFY, a Pioneer Transcription Factor in Plants: A Mini-Review

A subset of eukaryotic transcription factors (TFs) possess the ability to reprogram one cell type into another. Genes important for cellular reprograming are typically located in closed chromatin, which is covered by nucleosomes. Pioneer factors are a special class of TFs that can initially engage their target sites in closed chromatin prior to the engagement with, opening of, or modification of the sites by other factors. Although many pioneer factors are known in animals, a few have been characterized in plants. The TF LEAFY (LFY) acts as a pioneer factor specifying floral fate in Arabidopsis. In response to endogenous and environmental cues, plants produce appropriate floral inducers (florigens). During the vegetative phase, LFY is repressed by the TERMINAL FLOWER 1 (TFL1)–FD complex, which functions as a floral inhibitor, or anti-florigen. The florigen FLOWERING LOCUS T (FT) competes with TFL1 to prevent the binding of the FD TF to the LFY locus. The resulting FT–FD complex functions as a transient stimulus to activate its targets. Once LFY has been transcribed in the appropriate spatiotemporal manner, LFY binds to nucleosomes in closed chromatin regions. Subsequently, LFY opens the chromatin by displacing H1 linker histones and recruiting the SWI/SNF chromatin-remodeling complex. Such local changes permit the binding of other TFs, leading to the expression of the floral meristem identity gene APETALA1. This mini-review describes the latest advances in our understanding of the pioneer TF LFY, providing insight into the establishment of gene expression competence through the shaping of the plant epigenetic landscape.

ATFL1 (Anti-TFL1), a novel orthologue induces flowering in the masting alpine snow tussock, Chionochloa pallens (Poaceae)

Masting, the synchronous highly variable flowering across years by a population of perennial plants, has been shown to be precipitated by many factors including nitrogen levels, drought conditions, spring and summer temperatures. However, the molecular mechanism leading to the initiation of flowering in masting plants in particular years remains largely unknown, despite the potential impact of climate change on masting phenology. We studied genes controlling flowering in Chionochloa pallens, a strongly masting perennial grass. We used a range of in situ and manipulated plants to obtain leaf samples from tillers (shoots) which subsequently remained vegetative or flowered. Here, we show that a novel orthologue of TERMINAL FLOWER 1 (TFL1; normally a repressor of flowering in other species) promotes the induction of flowering in C. pallens (hence Anti-TFL1), a conclusion supported by structural, functional and expression analyses. Global transcriptomic analysis indicated differential expression of CpTPS1, CpGA20ox1, CpREF6 and CpHDA6, emphasising the role of endogenous cues and epigenetic regulation in terms of responsiveness of plants to initiate flowering. Our molecular-based study has provided insights into the cellular mechanism of flowering in masting plants and will supplement ecological and statistical models to predict how masting will respond to global climate change.

OsSPL9 Regulates Grain Number and Grain Yield in Rice

Rice grain yield consists of several key components, including tiller number, grain number per panicle (GNP), and grain weight. Among them, GNP is mainly determined by panicle branches and spikelet formation. In this study, we identified a gene affecting GNP and grain yield, OsSPL9, which encodes SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) family proteins. The mutation of OsSPL9 significantly reduced secondary branches and GNP. OsSPL9 was highly expressed in the early developing young panicles, consistent with its function of regulating panicle development. By combining expression analysis and dual-luciferase assays, we further confirmed that OsSPL9 directly activates the expression of RCN1 (rice TERMINAL FLOWER 1/CENTRORADIALIS homolog) in the early developing young panicle to regulate the panicle branches and GNP. Haplotype analysis showed that Hap3 and Hap4 of OsSPL9 might be favorable haplotypes contributing to high GNP in rice. These results provide new insights on high grain number breeding in rice.

The Branchless Gene C lbl in Watermelon Encoding a Terminal Flower 1 Protein Regulate S the Number of Lateral Branch

Lateral branching is one of the most important traits, which directly determines plant 27 architecture and crop productivity. Commercial watermelon has the characteristics of multiple 28 lateral branches, and it is time-consuming and labor costing to manually remove the lateral 29 branches in traditional watermelon cultivation. In our present study, a lateral branchless trait was 30 identified in watermelon material W CZ, and genetic analysis revealed that it was controlled by a 31 single recessive gene, which named as Clbl . A bulked segregant sequencing (BSA seq) and 32 linkage analysis was conducted to primarily mapping of Clbl on watermelon chromosome 4 33 Next-generation sequencing aided marker discovery and a large mapping population consisting of 34 1406 F 2 plants was used to further mapped the Clbl locus into a 9011 bp candidate region which 35 harbored only one candidate gene Cla018392 encoding a TERMINAL FLOWER 1 gene. Sequence 36 comparison of Cla018392 between two parental lines revealed that there was a SNP detected from 37 C to A in the coding region in the branchless inbred line WCZ , which resulted in a mutation of 38 Alanine (GCA) to Glutamate (GAA) at the fourth exon A dCAPS marker was developed from the 39 SNP locus, which was co-segregated with the branchless phenotype in both BC 1 and F 2 population, 40 and it was also further validated in 152 natural watermelon accessions. qRT PCR and in situ 41 hybridization showed that the expression levels of Cla0 18392 was significantly reduced in the 42 axillary bud and apical bud in the branchless line WCZ Ectopic expression of ClTFL1 in 43 Arabidopsis showed an increased number of lateral branches. The results of this study will be 44 useful for better understanding the molecular mechanism of lateral branch development in 45 watermelon and for the development of marker-assisted selection (MAS) for new branchless 46 watermelon cultivars.

Structural Changes and Adaptative Evolutionary Constraints In FLOWERING LOCUS T and TERMINAL FLOWER1-Like Genes of Flowering Plants

Regulation of flowering is a crucial event in the evolutionary history of angiosperms. The production of flowers is regulated through the integration of different environmental and endogenous stimuli, many of which involve the activation of different genes in a hierarchical and complex signaling network. The FLOWERING LOCUS T/TERMINAL FLOWER 1 (FT/TFL1) gene family is known to regulate important aspects of flowering in plants. To better understand the pivotal events that changed FT and TFL1 functions during the evolution of angiosperms, we reconstructed the ancestral sequences of FT/TFL1-like genes and predicted protein structures to identify determinant sites that evolved in both proteins and allowed the adaptative diversification in the flowering phenology and developmental processes. Residues from the P-loop domain of the analyzed FT structures showed predominantly high destabilizing mutations which is consistent with constant selective pressure found for this region. In addition, we demonstrate that the occurrence of destabilizing mutations in residues located at the phosphatidylcholine binding sites of FT structure experience positive selection, and some residues of 4th exon are under negative selection, which is compensated by the occurrence of stabilizing mutations in key regions and the P-loop to maintain the overall protein stability. Our results shed light on the evolutionary history of key genes involved in the diversification of angiosperms.

ATFL1 (Anti-TFL1), a novel orthologue induces flowering in the masting alpine snow tussock, Chionochloa pallens (Poaceae)

Masting, the synchronous highly variable flowering across years by a population of perennial plants, has been shown to be precipitated by many factors including nitrogen levels, drought conditions, spring and summer temperatures. However, the molecular mechanism leading to the initiation of flowering in masting plants in particular years remains largely unknown, despite the potential impact of climate change on masting phenology. We studied genes controlling flowering in Chionochloa pallens, a strongly masting perennial grass. We used a range of in situ and manipulated plants to obtain leaf samples from tillers (shoots) which subsequently remained vegetative or flowered. Here, we show that a novel orthologue of TERMINAL FLOWER 1 (TFL1; normally a repressor of flowering in other species) promotes the induction of flowering in C. pallens (hence Anti-TFL1), a conclusion supported by structural, functional and expression analyses. Global transcriptomic analysis indicated differential expression of CpTPS1, CpGA20ox1, CpREF6 and CpHDA6, emphasising the role of endogenous cues and epigenetic regulation in terms of responsiveness of plants to initiate flowering. Our molecular-based study has provided insights into the cellular mechanism of flowering in masting plants and will supplement ecological and statistical models to predict how masting will respond to global climate change.