Arabidopsis SEC13B Interacts with Suppressor of Frigida 4 to Repress Flowering

TOUSLED KINASE INTERACTING PROTEIN 1 (TKI1) interacts with SIN3-LIKES (SNLs) to promote flowering in Arabidopsis

TOUSLED KINASE INTERACTING PROTEIN 1 (TKI1) is a SANT/Myb domain-containing protein, which binds DNA and may function as a transcription factor, and is characterized as an interacting protein with TOUSLED (TSL) in Arabidopsis. However, it remains largely unknown what biological functions of TKI1 for few reports about TKI1 in the literature. Here we first identified that TKI1 interacts with SIN3-LIKEs (SNLs) and the responsible interaction domains are the C-terminal domain of TKI1 and the PAH (Paired Amphipathic Helix) domains of SNLs respectively in yeast. Then, we further confirmed the interactions between TKI1 and SNLs (SNL1-SNL6) in vitro or in vivo using multiple different protein-protein interaction methods. In addition, TKI1 and SNL3 are co-expressed in all the examined tissues here, and TKI1 and SNL3 are co-localized in the nucleus, indicating they may function together in plant. Furthermore, Genetic analysis with knockout mutants showed that both TKI1 and SNLs promote flowering with an additive effect in long days (LDs), however TKI1 induces flowering but SNLs inhibit flowering in short days (SDs). Finally, the flowering repressor FLOWERING LOCUS C (FLC) and its homolog MADS AFFECTING FLOWERING 4 (MAF4) were up-regulated, and the flowering activator FLOWERING LOCUS T (FT) and CONSTANS (CO) were down-regulated in tki1, snl1/2/3/4/5 and snl1/2/3/4/5 tki1 mutants, compared with Col-0. Therefore, our results increase our understanding of the biological functions of TKI1, and reveal that TKI1 physically interacts with SNLs and they both induce flowering in LDs, and indicate that TKI1 and SNLs may function together to regulate flowering gene expression to promote flowering in Arabidopsis.

SUPPRESSOR OF FRIGIDA 4 cooperates with the histone methylation reader EBS to positively regulate root development

Maintenance and homeostasis of the quiescent center (QC) in Arabidopsis (Arabidopsis thaliana) root apical meristems are critical for stem cell organization and root development. Despite great progress in relevant research, the molecular mechanisms that determine the root stem cell fate and QC still need further exploration. In Arabidopsis, SUPPRESSOR OF FRIGIDA 4 (SUF4) encodes a C2H2-type zinc finger protein that represses flowering by transcriptional activation of FLOWERING LOCUS C (FLC) through the FRIGIDA (FRI) pathway, and EARLY BOLTING IN SHORT DAYS (EBS) is a bivalent histone reader that prevents premature flowering. Here, we found that SUF4 directly interacts with EBS in vivo and in vitro. Loss of function of SUF4 and/or EBS resulted in disorganization of the QC, aberrant cell division, and stunted root growth. RNA-seq and reverse transcription quantitative real-time polymerase chain reaction analysis revealed that SUF4 and EBS coregulate many root development-related genes. A series of biochemical analyses demonstrated that SUF4 directly binds to the promoter of SCARECROW (SCR), which encodes a key regulator of root development. Chromatin immunoprecipitation assay indicated that both SUF4 and EBS are recruited to the SCR locus in an interdependent manner to promote H3K4me3 levels and suppress H3K27me3 levels, thereby activating the expression of SCR. These findings improve our understanding of the function of SUF4 and EBS and provide insights into the molecular mechanism that couples a transcription factor and a histone methylation reader to modulate QC specification and root development in Arabidopsis.

Genome-wide identification and characterization of flowering genes in Citrus sinensis (L.) Osbeck: a comparison among C. Medica L., C. Reticulata Blanco, C. Grandis (L.) Osbeck and C. Clementina

BACKGROUND

Flowering plays an important role in completing the reproductive cycle of plants and obtaining next generation of plants. In case of citrus, it may take more than a year to achieve progeny. Therefore, in order to fasten the breeding processes, the juvenility period needs to be reduced. The juvenility in plants is regulated by set of various flowering genes. The citrus fruit and leaves possess various medicinal properties and are subjected to intensive breeding programs to produce hybrids with improved quality traits. In order to break juvenility in Citrus, it is important to study the role of flowering genes. The present study involved identification of genes regulating flowering in Citrus sinensis L. Osbeck via homology based approach. The structural and functional characterization of these genes would help in targeting genome editing techniques to induce mutations in these genes for producing desirable results.

RESULTS

A total of 43 genes were identified which were located on all the 9 chromosomes of citrus. The in-silico analysis was performed to determine the genetic structure, conserved motifs, cis-regulatory elements (CREs) and phylogenetic relationship of the genes. A total of 10 CREs responsible for flowering were detected in 33 genes and 8 conserved motifs were identified in all the genes. The protein structure, protein-protein interaction network and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was performed to study the functioning of these genes which revealed the involvement of flowering proteins in circadian rhythm pathways. The gene ontology (GO) and gene function analysis was performed to functionally annotate the genes. The structure of the genes and proteins were also compared among other Citrus species to study the evolutionary relationship among them. The expression study revealed the expression of flowering genes in floral buds and ovaries. The qRT-PCR analysis revealed that the flowering genes were highly expressed in bud stage, fully grown flower and early stage of fruit development.

CONCLUSIONS

The findings suggested that the flowering genes were highly conserved in citrus species. The qRT-PCR analysis revealed the tissue specific expression of flowering genes (CsFT, CsCO, CsSOC, CsAP, CsSEP and CsLFY) which would help in easy detection and targeting of genes through various forward and reverse genetic approaches.