Characteristics and expression of the TCP transcription factors family in Allium senescens reveal its potential roles in drought stress responses

Allium senescens,is an important economic and ecological grassland plant with drought-resistant characteristics.A TCP protein transcription factor is important in the regulation of plant development and adverse responses.However,the mechanism by which TCP transcription functions in drought resistance in Allium senescens is still not clear.Here,we obtained a total of 190,305 transcripts with 115,562 single gene clusters based on RNA-Seq sequencing of Allium senescens under drought stress.The total number of bases was 97,195,096 bp,and the average length was 841.06 bp.Furthermore,we found that there were eight genes of the TCP family that showed an upregulated expression trend under drought stress in Allium senescens.We carried out an investigation to determine the evolution and function of the AsTCP family and how they produce an effect in drought resistance.The 14 AsTCP genes were confirmed and divided into class I and class II containing CIN and CYC/TBI subfamilies,respectively.We also found that the expression of AsTCP17 was remarkably upregulated with drought treatment.Besides,the transformation of AsTCP17 in Arabidopsis revealed that the protective enzymes,namely polyphenol oxidase(POD)and superoxide dismutase(SOD),were increased by 0.4 and 0.8 times,respectively.Chlorophyll content was also increased,while the H2O2 and malondialdehyde(MDA)contents were decreased.Staining assays with 3,3′-diaminobenzidine(DAB)also suggested that the AsTCP17 downregulates reactive oxygen species(ROS)accumulation.In addition,overexpression of the AsTCP17 affected the accumulation of drought-related hormones in plants,and the synthesis of ABA.The expression of AtSVP and AtNCED3,related ABA synthesis pathway genes,indicated that the level of expression of AtSVP and AtNCED3 was obviously enhanced,with the overexpression of line 6 showing a 20.6-fold and 7.0-fold increase,respectively.Taken together,our findings systematically analyze the AsTCPs family at the transcriptome expression level in Allium senescens,and we also demonstrated that AsTCP17 protein,as a positive regulator,was involved in drought resistance of Allium senescens.In addition,our research contributes to the comprehensive understanding of the drought stress defense mechanism in herbaceous plants.

Rare SNP Identified a TCP Transcription Factor Essential for Tendril Development in Cucumber

Rare genetic variants are abundant in genomes but less tractable in genome-wide association study. Here we exploit a strategy of rare variation mapping to discover a gene essential for tendril development in cucumber （Cucumis sativus L.）. In a collection of 〉3000 lines, we discovered a unique tendril-less line that forms branches instead of tendrils and, therefore, loses its climbing ability. We hypothesized that this unusual phenotype was caused by a rare variation and subsequently identified the causative single nucleotide poly- morphism. The affected gene TEN encodes a TCP transcription factor conserved within the cucurbits and is expressed specifically in tendrils, representing a new organ identity gene. The variation occurs within a pro- tein motif unique to the cucurbits and impairs its function as a transcriptional activator. Analyses of transcrip- tomes from near-isogenic lines identified downstream genes required for the tendril＇s capability to sense and climb a support. This study provides an example to explore rare functional variants in plant genomes.

BrrTCP4b interacts with BrrTTG1 to suppress the development of trichomes in Brassica rapa var. rapa

The number of trichomes significantly increased in CRISPR/Cas9-edited BrrTCP4b turnip(Brassica rapa var.rapa)plants.However,the underlying molecular mechanism remains to be uncovered.In this study,we performed the Y2H screen using BrrTCP4b as the bait,which unveiled an interaction between BrrTCP4b and BrrTTG1,a pivotal WD40-repeat protein transcription factor in the MYB-bHLH-WD40(MBW)complex.This physical interaction was further validated through bimolecular luciferase complementation and co-immunoprecipitation.Furthermore,it was found that the interaction between BrrTCP4b and BrrTTG1 could inhibit the activity of MBW complex,resulting in decreased expression of BrrGL2,a positive regulator of trichomes development.In contrast,AtTCP4 is known to regulate trichomes development by interacting with AtGL3 in Arabidopsis thaliana.Overall,this study revealed that BrrTCP4b is involved in trichome development by interacting with BrrTTG1 in turnip,indicating a divergence from the mechanisms observed in model plant A.thaliana.The findings contribute to our understanding of the regulatory mechanisms governing trichome development in the non-model plants turnip.

Histone methylation readers MRG1/MRG2 interact with the transcription factor TCP14 to positively modulate cytokinin sensitivity in Arabidopsis

Cytokinins influence many aspects of plant growth and development.Although cytokinin biosynthesis and signaling have been well studied in planta,little is known about the regulatory effects of epigenetic modifications on the cytokinin response.Here,we reveal that mutations to Morf Related Gene(MRG)proteins MRG1/MRG2,which are readers of trimethylated histone H3 lysine 4 and lysine 36(H3K4me3 and H3K36me3),result in cytokinin hyposensitivity during various developmental processes,including callus induction and root and seedling growth inhibition.Similar to the mrg1 mrg2 mutant,plants with a defective AtTCP14,which belongs to the TEOSINTE BRANCHED,CYCLOIDEA,AND PROLIFERATING CELL FACTOR(TCP)transcription factor family,are insensitive to cytokinin.Furthermore,the transcription of several genes related to cytokinin signaling pathway is altered.Specifically,the expression of Arabidopsis thaliana HISTIDINE-CONTAINING PHOSPHOTRANSMITTER PROTEIN 2(AHP2)decreases significantly in the mrg1 mrg2 and tcp14-2 mutants.We also confirm the interaction between MRG2 and TCP14 in vitro and in vivo.Thus,MRG2 and TCP14 can be recruited to AHP2 after recognizing H3K4me3/H3K36me3 markers and promote the histone-4 lysine-5 acetylation to further enhance AHP2 expression.In summary,our research elucidate a previously unknown mechanism mediating the effects of MRG proteins on the magnitude of the cytokinin response.

The Arabidopsis Transcription Factor AtTCP15 Regulates Endoreduplication by Modulating Expression of Key Cell-cycle Genes

Plant cells frequently undergo endoreduplication, a modified cell cycle in which genome is repeatedly rep- licated without cytokinesis. As the key step to achieve final size and function for cells, endoreduplication is prevalent during plant development. However, mechanisms to control the balance between endoreduplication and mitotic cell di- vision are still poorly understood. Here, we show that the Arabidopsis TCP （CINCINNATA-like TEOSINTE BRANCHED1~ CYCLOIDEA-_PCF）-family transcription factor gene AtTCP15 is expressed in trichomes, as well as in rapidly dividing and vascular tissues. Expression of AtTCP15SRDX, AtTCP15 fused with a SRDX repressor domain, induces extra endoredupli- cation in trichomes and cotyledon cells in transgenic Arabidopsis. On the contrary, overexpression of AtTCP15 suppresses endoreduplication in trichomes and other examined cells. Misregulation of AtTCP15 affects the expression of several im- portant genes involved in cell-cycle regulation. AtTCP15 protein binds directly to the promoter regions of CYCA2;3 and RETINOBLASTOMA-RELATED （RBR） genes, which play key roles in endoreduplication. Taken together, AtTCP15 plays an important role in regulating endoreduplication during Arabidopsis development.

Arabidopsis transcription factor TCP4 represses chlorophyll biosynthesis to prevent petal greening

Green petals pose a challenge for pollinators to distinguish flowers from leaves,but they are valuable as a specialty flower trait.However,little is understood about the molecular mechanisms that underlie the development of green petals.Here,we report that CINCINNATA(CIN)-like TEOSINTE BRANCHED 1/CYCLOIDEA/PCF(TCP)proteins play key roles in the control of petal color.The septuple tcp2/3/4/5/10/13/17 mutant produced flowers with green petals due to chlorophyll accumulation.Expression of TCP4 complemented the petal phenotype of tcp2/3/4/5/10/13/17.We found that chloroplasts were converted into leucoplasts in the distal parts of wild-type petals but not in the proximal parts during flower development,whereas plastid conversion was compromised in the distal parts of tcp2/3/4/5/10/13/17 petals.TCP4 and most CIN-like TCPs were predominantly expressed in distal petal regions,consistent with the green–white pattern in wild-type petals and the petal greening observed in the distal parts of tcp2/3/4/5/10/13/17 petals.RNA-sequencing data revealed that most chlorophyll biosynthesis genes were downregulated in the white distal parts of wild-type petals,but these genes had elevated expression in the distal green parts of tcp2/3/4/5/10/13/17 petals and the green proximal parts of wild-type petals.We revealed that TCP4 repressed chlorophyll biosynthesis by directly binding to the promoters of PROTOCHLOROPHYLLIDE REDUCTASE(PORB),DIVINYL REDUCTASE(DVR),and SUPPRESSOR OF OVEREXPRESSION OF CO 1(SOC1),which are known to promote petal greening.We found that the conversion of chloroplasts to leucoplasts and the green coloration in the proximal parts of petals appeared to be conserved among plant species.Our findings uncover a major molecular mechanism that underpins the formation of petal color patterns and provide a foundation for the breeding of plants with green flowers.

Activation tagging identifies WRKY14 as a repressor of plant thermomorphogenesis in Arabidopsis

Increases in recorded high temperatures around the world are causing plant thermomorphogenesis and decreasing crop productivity.PHYTOCHROME INTERACTING FACTOR 4(PIF4)is a central positive regulator of plant thermomorphogenesis.However,the molecular mechanisms underlying PIF4-regulated thermomorphogenesis remain largely unclear.In this study,we identified ABNORMAL THERMOMORPHOGENESIS 1(ABT1)as an important negative regulator of PIF4 and plant thermomorphogenesis.Overexpression of ABT1 in the activation tagging mutant abt1-D caused shorter hypocotyls and petioles under moderately high temperature(HT).ABT1 encodes WRKY14,which belongs to subgroup II of the WRKY transcription factors.Overexpression of ABT1/WRKY14 or its close homologs,including ABT2/WRKY35,ABT3/WRKY65,and ABT4/WRKY69in transgenic plants caused insensitivity to HT,whereas the quadruple mutant abt1 abt2 abt3 abt4 exhibited greater sensitivity to HT.ABTs were expressed in hypocotyls,cotyledons,shoot apical meristems,and leaves,but their expression were suppressed by HT.Biochemical assays showed that ABT1 can interact with TCP5,a known positive regulator of PIF4,and interrupt the formation of the TCP5-PIF4 complex and repress its transcriptional activation activity.Genetic analysis showed that ABT1 functioned antagonistically with TCP5,BZR1,and PIF4 in plant thermomorphogenesis.Taken together,our results identify ABT1/WRKY14 as a critical repressor of plant thermomorphogenesis and suggest that ABT1/WRKY14,TCP5,and PIF4 may form a sophisticated regulatory module to fine-tune PIF4 activity and temperature-dependent plant growth.