Project description:Plants have evolved a unique and conserved developmental program that enables the conversion of leaves into floral organs. Elegant genetic and molecular work has identified key regulators of floral meristem identity. However, further understanding of flower meristem specification has been hampered by redundancy and by pleiotropic effects. The KNOXI gene STM transcription factor is a well-characterized regulator of shoot apical meristem maintenance. stm loss-of-function mutants arrest shortly after germination, and therefore the knowledge on later roles of STM, including flower development, is limited. Here, we uncover a role for STM in the specification of flower meristem identity. Silencing STM in the AP1 expression domain in the ap1-4 mutant background resulted in a complete leafy-like flower phenotype and an intermediate stm-2 allele enhanced the floral meristem identity phenotype of ap1-4. Transcriptional profiling of STM perturbation suggested that STM activity affects multiple meristem identity and flower transition genes, among them the F-Box gene UFO. In agreement, stm-2 enhanced the ufo-2 floral meristem fate phenotype, and ectopic UFO expression rescued the leafy flowers in genetic backgrounds with compromised AP1 and STM activities. This work suggests a molecular mechanism that underlies the activity of STM in the specification of flower meristem identity.
Project description:The transcription factors LEAFY (LFY) and APETALA1 (AP1)_together with the AP1 paralog CAULIFLOWER (CAL)_control the onRep_of flower development in a partially redundant manner. This redundancy is thought to be mediated_at least in part_through the regulation of a shared Rep_of target genes. However_whether these genes are independently or cooperatively regulated by LFY and AP1/CAL_is currently unknown. To better understand the regulatory relationship between LFY and AP1/CAL during floral initiation_we monitored the activity of LFY in the absence of AP1/CAL function. We found that the regulation of several known LFY target genes is unaffected by AP1/CAL perturbation_while others appear to require AP1/CAL activity. Furthermore_we obtained evidence that LFY and AP1/CAL control the expression of some genes in an antagonistic manner. Notably_these include key regulators of floral initiation such TERMINAL FLOWER1 (TFL1)_which had been previously reported to be directly repressed by both LFY and AP1. We show here that TFL1 expression is suppressed by AP1 but promoted by LFY. We further demonstrate that LFY has an inhibitory effect on flower formation in the absence of AP1/CAL activity. We propose that LFY and AP1/CAL may act as part of an incoherent feed-forward loop to control the establishment of a stable developmental program for the formation of flowers.
Project description:We studied early events of flower formation with a temporal resolution by employing a floral induction system to drive synchronized flower development from inflorescence meristem-like tissue (Wellmer et al. (2006)). We generated a developmental time series including vegetative leaf tissue, young developing flowers at zero (t0) and two days after induction of flower development (t2), and fully expanded inflorescences. Although we found very similar numbers of H3K27me3 and H3K4me3 target genes, many genes display quantitative changes in those marks, especially between different tissue types (e.g. >60% of target genes change quantitatively from leaf to t0).
Project description:Despite great advances in sequencing capacity, generating functional information for non-model organisms remains a challenge. One solution lies in an improved ability to predict genetic circuits based on primary DNA sequence combined with the characterization of regulatory molecules from model species. Here, we focus on the LEAFY (LFY) transcription factor, a conserved master regulator of floral development. Starting with biochemical and structural information, we built a biophysical model describing LFY DNA binding specificity in vitro that accurately predicts in vivo LFY binding sites in the Arabidopsis thaliana genome. Extending the model to other species, we show that it can correctly identify functional homologs of known LFY targets from Arabidopsis thaliana in other angiosperms, even if a functional shift between orthologs and paralogs has occurred. Moreover, this model demonstrates the evolutionary fluidity of the link between LFY and one of its target genes, underlining how this regulatory interaction can be conserved despite changes in position, sequence and affinity of the LFY binding sites. Our study shows that the cis-element fluidity recently illustrated in animals also exists in plants, and that it can be detected without any experimental work in each individual species, using a biophysical transcription factor model. A. thaliana LEAFY ChIP-seq w control, 2 replicates
Project description:The transcription factors LEAFY (LFY) and APETALA1 (AP1), together with the AP1 paralog CAULIFLOWER (CAL), control the onset of flower development in a partially redundant manner. This redundancy is thought to be mediated, at least in part, through the regulation of a shared set of target genes. However, whether these genes are independently or cooperatively regulated by LFY and AP1/CAL, is currently unknown. To better understand the regulatory relationship between LFY and AP1/CAL during floral initiation, we monitored the activity of LFY in the absence of AP1/CAL function. We found that the regulation of several known LFY target genes is unaffected by AP1/CAL perturbation, while others appear to require AP1/CAL activity. Furthermore, we obtained evidence that LFY and AP1/CAL control the expression of some genes in an antagonistic manner. Notably, these include key regulators of floral initiation such TERMINAL FLOWER1 (TFL1), which had been previously reported to be directly repressed by both LFY and AP1. We show here that TFL1 expression is suppressed by AP1 but promoted by LFY. We further demonstrate that LFY has an inhibitory effect on flower formation in the absence of AP1/CAL activity. We propose that LFY and AP1/CAL may act as part of an incoherent feed-forward loop to control the establishment of a stable developmental program for the formation of flowers.
Project description:miRNAs-mediated gene silencing pathway plays vital roles in plant development, abiotic and biotic stress responses. Here, we carried out a high-throughput sequencing approach to identify miRNAs targets in leaves, flowers and fruit of sweet orange.C onsequently, 55257, 62365 and 19393 degraded mRNA fragments were identified in leaf, flower and fruit, respectively.