Class I TCP transcription factors regulate trichome branching and cuticle development in Arabidopsis

NtWIN1 regulates the biosynthesis of scopoletin and chlorogenic acid by targeting NtF6'H1 and NtCCoAMT genes in Nicotiana tabacum

Scopoletin and chlorogenic acid (CGA) are important polyphenols that regulate plant growth, development, and stress resistance. The ERF transcription factor WAX INDUCER1 (WIN1) promotes the biosynthesis of cutin, suberine, and wax. However, its full roles in regulating the accumulation of plant secondary metabolites still remain to be further clarified. In this study, NtWIN1 gene encoding a SHINE-type AP2/ERF transcription factor of the Va subgroup was identified from N. tabacum. NtWIN1 showed high expression levels in tobacco stems, sepals, and pistils. Overexpression (OE) and knock-out of NtWIN1 showed that it promoted the accumulation of total polyphenols and altered their composition. Compare to that of WT plants, the CGA contents significantly increased by 25%-50% in the leaves, flowers, and capsules of OE lines, while the scopoletin contents in the OE plants significantly decreased by 30%-67%. In contrast, the CGA contents in ntwin1 lines reduced by 23%-26%, and the scopoletin contents in ntwin1 increased by 38%-75% compare to that of WT plants. Chromatin immunoprecipitation and Dual-Luc transcription activation assays showed that NtWIN1 could bind to the promoters of NtF6'H1 and NtCCoAMT, thereby modulating their expression. The scopoletin content in ntwin1/ntf6'h1 double mutant was significantly lower than that in ntwin1 and WT plants, but showed no significant differences with that in ntf6'h1 mutant, further indicating that the inhibition of NtWIN1 on scopoletin accumulation depends on the activity of NtF6'H1. Our study illustrates the new roles of NtWIN1, and provides a possible target for regulating the synthesis of polyphenols in tobacco.

Class I TCP transcription factors TCP14 and TCP15 promote axillary branching in Arabidopsis by counteracting the action of Class II TCP BRANCHED1

Shoot branching is determined by a balance between factors that promote axillary bud dormancy and factors that release buds from the quiescent state. The TCP family of transcription factors is classified into two classes, Class I and Class II, which usually play different roles. While the role of the Class II TCP BRANCHED1 (BRC1) in suppressing axillary bud development in Arabidopsis thaliana has been widely explored, the function of Class I TCPs in this process remains unknown. We analyzed the role of Class I TCP14 and TCP15 in axillary branch development in Arabidopsis through a series of genetic and molecular studies. In contrast to the increased branch number shown by brc1 mutants, tcp14 tcp15 plants exhibit a reduced number of branches compared with wild-type. Our findings provide evidence that TCP14 and TCP15 act by counteracting BRC1 function through two distinct mechanisms. First, they indirectly reduce BRC1 expression levels. Additionally, TCP15 directly interacts with BRC1 decoying it from chromatin and thereby preventing the transcriptional activation of a set of BRC1-dependent genes. We describe a molecular mechanism by which Class I TCPs physically antagonize the action of the Class II TCP BRC1, aligning with their opposite roles in axillary bud development.

A cotton endoreduplication gene, GaTOP6B, regulates trichome branching development

Trichomes are specialized epidermal structures that protect plants from biotic and abiotic stresses by synthesizing, storing, and secreting defensive compounds. This study investigates the role of the Gossypium arboreum DNA topoisomerase VI subunit B gene (GaTOP6B) in trichome development and branching. Sequence alignment revealed a high similarity between GaTOP6B and AtTOP6B, suggesting a conserved function in trichome regulation. Although AtTOP6B acts as a positive regulator of trichome development, functional analyses showed contrasting effects: Virus-induced gene silencing (VIGS) of GaTOP6B in cotton increased trichome density, while its overexpression in Arabidopsis decreased trichome density but enhanced branching. This demonstrates that GaTOP6B negatively regulates trichome number, indicating species-specific roles in trichome initiation and branching between cotton and Arabidopsis. Overexpression of the GaTOP6B promotes jasmonic acid synthesis, which in turn inhibits the G1/S or G2/M transitions, stalling the cell cycle. On the other hand, it suppresses brassinolide synthesis and signaling while promoting cytokinin degradation, further inhibiting mitosis. These hormonal interactions facilitate the transition of cells from the mitotic cycle to the endoreduplication cycle. As the level of endoreduplication increases, trichomes develop an increased number of branches. These findings highlight GaTOP6B's critical role as a regulator of trichome development, providing new genetic targets for improving cotton varieties in terms of enhanced adaptability and resilience.

Abscisic acid controls sugar accumulation essential to strawberry fruit ripening via the FaRIPK1-FaTCP7-FaSTP13/FaSPT module

Strawberry is considered as a model plant for studying the ripening of abscisic acid (ABA)-regulated non-climacteric fruits, a process in which sugar plays a fundamental role, while how ABA regulates sugar accumulation remains unclear. This study provides a direct line of physiological, biochemical, and molecular evidence that ABA signaling regulates sugar accumulation via the FaRIPK1-FaTCP7-FaSTP13/FaSPT signaling pathway. Herein, FaRIPK1, a red-initial protein kinase 1 previously identified in strawberry fruit, not only interacted with the transcription factor FaTCP7 (TEOSINTE BRANCHEN 1, CYCLOIDEA, and PCF) but also phosphorylated the critical Ser89 and Thr93 sites of FaTCP7, which negatively regulated strawberry fruit ripening, as evidenced by the transient overexpression (OE) and virus-induced gene silencing transgenic system. Furthermore, the DAP-seq experiments revealed that FvTCP7 bound the motif "GTGGNNCCCNC" in the promoters of two sugar transporter genes, FaSTP13 (sugar transport protein 13) and FaSPT (sugar phosphate/phosphate translocator), inhibiting their transcription activities as determined by the electrophoretic mobility shift assay, yeast one-hybrid, and dual-luciferase reporter assays. The downregulated FaSTP13 and FaSPT transcripts in the FaTCP7-OE fruit resulted in a reduction in soluble sugar content. Consistently, the yeast absorption test revealed that the two transporters had hexose transport activity. Especially, the phosphorylation-inhibited binding of FaTCP7 to the promoters of FaSTP13 and FaSPT could result in the release of their transcriptional activities. In addition, the phosphomimetic form FaTCP7S89D or FaTCP7T93D could rescue the phenotype of FaTCP7-OE fruits. Importantly, exogenous ABA treatment enhanced the FaRIPK1-FaTCP7 interaction. Overall, we found direct evidence that ABA signaling controls sugar accumulation during strawberry fruit ripening via the "FaRIPK1-FaTCP7-FaSTP13/FaSPT" module.

Class I TCP in fruit development: much more than growth

Fruit development can be viewed as the succession of three main steps consisting of the fruit initiation, growth and ripening. These processes are orchestrated by different factors, notably the successful fertilization of flowers, the environmental conditions and the hormones whose action is coordinated by a large variety of transcription factors. Among the different transcription factor families, TEOSINTE BRANCHED 1, CYCLOIDEA, PROLIFERATING CELL FACTOR (TCP) family has received little attention in the frame of fruit biology despite its large effects on several developmental processes and its action as modulator of different hormonal pathways. In this respect, the comprehension of TCP functions in fruit development remains an incomplete puzzle that needs to be assembled. Building on the abundance of genomic and transcriptomic data, this review aims at collecting available TCP expression data to allow their integration in the light of the different functional genetic studies reported so far. This reveals that several Class I TCP genes, already known for their involvement in the cell proliferation and growth, display significant expression levels in developing fruit, although clear evidence supporting their functional significance in this process remains scarce. The extensive expression data compiled in our study provide convincing elements that shed light on the specific involvement of Class I TCP genes in fruit ripening, once these reproductive organs acquire their mature size. They also emphasize their putative role in the control of specific biological processes such as fruit metabolism and hormonal dialogue.

TrichomeLess Regulator 3 is required for trichome initial and cuticle biosynthesis in Artemisia annua

Artemisinin is primarily synthesized and stored in the subepidermal space of the glandular trichomes of Artemisia annua. The augmentation of trichome density has been demonstrated to enhance artemisinin yield. However, existing literature lacks insights into the correlation between the stratum corneum and trichomes. This study aims to unravel the involvement of TrichomeLess Regulator 3 (TLR3), which encodes the transcription factor, in artemisinin biosynthesis and its potential association with the stratum corneum. TLR3 was identified as a candidate gene through transcriptome analysis. The role of TLR3 in trichome development and morphology was investigated using yeast two-hybrid, pull-down analysis, and RNA electrophoresis mobility assay. Our research revealed that TLR3 negatively regulates trichome development. It modulates the morphology of Arabidopsis thaliana trichomes by inhibiting branching and inducing the formation of abnormal trichomes in Artemisia annua. Overexpression of the TLR3 gene disrupts the arrangement of the stratum corneum and reduces artemisinin content. Simultaneously, TLR3 possesses the capacity to regulate stratum corneum development and trichome follicle morphology by interacting with TRICHOME AND ARTEMISININ REGULATOR 1, and CycTL. Consequently, our findings underscore the pivotal role of TLR3 in the development of glandular trichomes and stratum corneum biosynthesis, thereby influencing the morphology of Artemisia annua trichomes.

Mapping and Detection of Genes Related to Trichome Development in Black Gram (Vigna mungo (L.) Hepper)

Black gram (Vigna mungo (L.) Hepper) is a pulses crop with good digestible protein and a high carbohydrate content, so it is widely consumed as human food and animal feed. Trichomes are large, specialized epidermal cells that confer advantages on plants under biotic and abiotic stresses. Genes regulating the development of trichomes are well characterized in Arabidopsis and tomato. However, little is known about trichome development in black gram. In this study, a high-density map with 5734 bin markers using an F2 population derived from a trichome-bearing and a glabrous cultivar of black gram was constructed, and a major quantitative trait locus (QTL) related to trichomes was identified. Six candidate genes were located in the mapped interval region. Fourteen single-nucleotide polymorphisms (SNPs) or insertion/deletions (indels) were associated with those genes. One indel was located in the coding region of the gene designated as Scaffold_9372_HRSCAF_11447.164. Real-time quantitative PCR (qPCR) analysis demonstrated that only one candidate gene, Scaffold_9372_HRSCAF_11447.166, was differentially expressed in the stem between the two parental lines. These two candidate genes encoded the RNA polymerase-associated protein Rtf1 and Bromodomain adjacent to zinc finger domain protein 1A (BAZ1A). These results provide insights into the regulation of trichome development in black gram. The candidate genes may be useful for creating transgenic plants with improved stress resistance and for developing molecular markers for trichome selection in black gram breeding programs.

OsTCP19 coordinates inhibition of lignin biosynthesis and promotion of cellulose biosynthesis to modify lodging resistance in rice

Lignin and cellulose are two essential elements of plant secondary cell walls that shape the mechanical characteristics of the culm to prevent lodging. However, how the regulation of the lignin and cellulose composition is combined to achieve optimal mechanical characteristics is unclear. Here, we show that increasing OsTCP19 expression in rice coordinately repressed lignin biosynthesis and promoted cellulose biosynthesis, resulting in enhanced lodging resistance. In contrast, repression of OsTCP19 coordinately promoted lignin biosynthesis and inhibited cellulose biosynthesis, leading to greater susceptibility to lodging. We found that OsTCP19 binds to the promoters of both MYB108 and MYB103L to increase their expression, with the former being responsible for repressing lignin biosynthesis and the latter for promoting cellulose biosynthesis. Moreover, up-regulation of OsTCP19 in fibers improved grain yield and lodging resistance. Thus, our results identify the OsTCP19-OsMYB108/OsMYB103L module as a key regulator of lignin and cellulose production in rice, and open up the possibility for precisely manipulating lignin-cellulose composition to improve culm mechanical properties for lodging resistance.

Single-Cell Transcriptome Atlas and Regulatory Dynamics in Developing Cotton Anthers

Plant anthers are composed of different specialized cell types with distinct roles in plant reproduction. High temperature (HT) stress causes male sterility, resulting in crop yield reduction. However, the spatial expression atlas and regulatory dynamics during anther development and in response to HT remain largely unknown. Here, the first single-cell transcriptome atlas and chromatin accessibility survey in cotton anther are established, depicting the specific expression and epigenetic landscape of each type of cell in anthers. The reconstruction of meiotic cells, tapetal cells, and middle layer cell developmental trajectories not only identifies novel expressed genes, but also elucidates the precise degradation period of middle layer and reveals a rapid function transition of tapetal cells during the tetrad stage. By applying HT, heterogeneity in HT response is shown among cells of anthers, with tapetal cells responsible for pollen wall synthesis are most sensitive to HT. Specifically, HT shuts down the chromatin accessibility of genes specifically expressed in the tapetal cells responsible for pollen wall synthesis, such as QUARTET 3 (QRT3) and CYTOCHROME P450 703A2 (CYP703A2), resulting in a silent expression of these genes, ultimately leading to abnormal pollen wall and male sterility. Collectively, this study provides substantial information on anthers and provides clues for heat-tolerant crop creation.

Identification, evolution, and expression of GDSL-type Esterase/Lipase (GELP) gene family in three cotton species: a bioinformatic analysis

BACKGROUND

GDSL esterase/lipases (GELPs) play important roles in plant growth, development, and response to biotic and abiotic stresses. Presently, an extensive and in-depth analysis of GELP family genes in cotton is still not clear enough, which greatly limits the further understanding of cotton GELP function and regulatory mechanism.

RESULTS

A total of 389 GELP family genes were identified in three cotton species of Gossypium hirsutum (193), G. arboreum (97), and G. raimondii (99). These GELPs could be classified into three groups and eight subgroups, with the GELPs in same group to have similar gene structures and conserved motifs. Evolutionary event analysis showed that the GELP family genes tend to be diversified at the spatial dimension and certain conservative at the time dimension, with a trend of potential continuous expansion in the future. The orthologous or paralogous GELPs among different genomes/subgenomes indicated the inheritance from genome-wide duplication during polyploidization, and the paralogous GELPs were derived from chromosomal segment duplication or tandem replication. GELP genes in the A/D subgenome underwent at least three large-scale replication events in the evolutionary process during the period of 0.6-3.2 MYA, with two large-scale evolutionary events between 0.6-1.8 MYA that were associated with tetraploidization, and the large-scale duplication between 2.6-9.1 MYA that occurred during diploidization. The cotton GELPs indicated diverse expression patterns in tissue development, ovule and fiber growth, and in response to biotic and abiotic stresses, combining the existing cis-elements in the promoter regions, suggesting the GELPs involvements of functions to be diversification and of the mechanisms to be a hormone-mediated manner.

CONCLUSIONS

Our results provide a systematic and comprehensive understanding the function and regulatory mechanism of cotton GELP family, and offer an effective reference for in-depth genetic improvement utilization of cotton GELPs.

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 thalianaHISTIDINE-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.

Knockout of floral and meiosis genes using CRISPR/Cas9 produces male-sterility in Eucalyptus without impacts on vegetative growth

Eucalyptus spp. are widely cultivated for the production of pulp, energy, essential oils, and as ornamentals. However, their dispersal from plantings, especially when grown as an exotic, can cause ecological disruptions. To provide new tools for prevention of sexual dispersal by pollen as well as to induce male-sterility for hybrid breeding, we studied the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated knockout of three floral genes in both FT-expressing (early-flowering) and non-FT genotypes. We report male-sterile phenotypes resulting from knockout of the homologs of all three genes, including one involved in meiosis and two regulating early stages of pollen development. The targeted genes were Eucalyptus homologs of REC8 (EREC8), TAPETAL DEVELOPMENT AND FUNCTION 1 (ETDF1), and HECATE3 (EHEC3-like). The erec8 knockouts yielded abnormal pollen grains and a predominance of inviable pollen, whereas the etdf1 and ehec3-like knockouts produced virtually no pollen. In addition to male-sterility, both erec8 and ehec3-like knockouts may provide complete sterility because the failure of erec8 to undergo meiosis is expected to be independent of sex, and ehec3-like knockouts produce flowers with shortened styles and no visible stigmas. When comparing knockouts to controls in wild-type (non-early-flowering) backgrounds, we did not find visible morphological or statistical differences in vegetative traits, including average single-leaf mass, stem volume, density of oil glands, or chlorophyll in leaves. Loss-of-function mutations in any of these three genes show promise as a means of inducing male- or complete sterility without impacting vegetative development.

Physiological Roles and Mechanisms of Action of Class I TCP Transcription Factors

TEOSINTE BRANCHED1, CYCLOIDEA, PROLIFERATING CELL FACTOR 1 and 2 (TCP) proteins constitute a plant-specific transcription factors family exerting effects on multiple aspects of plant development, such as germination, embryogenesis, leaf and flower morphogenesis, and pollen development, through the recruitment of other factors and the modulation of different hormonal pathways. They are divided into two main classes, I and II. This review focuses on the function and regulation of class I TCP proteins (TCPs). We describe the role of class I TCPs in cell growth and proliferation and summarize recent progresses in understanding the function of class I TCPs in diverse developmental processes, defense, and abiotic stress responses. In addition, their function in redox signaling and the interplay between class I TCPs and proteins involved in immunity and transcriptional and posttranslational regulation is discussed.

The N-terminal region located upstream of the TCP domain is responsible for the antagonistic action of the Arabidopsis thaliana TCP8 and TCP23 transcription factors on flowering time

TCP proteins (TCPs) are plant-exclusive transcription factors that exert effects on multiple aspects of plant development, from germination to flower and fruit formation. TCPs are divided into two main classes, I and II. In this study, we found that the Arabidopsis thaliana class I TCP transcription factor TCP8 is a positive regulator of flowering time. TCP8 mutation and constitutive expression delayed and accelerated flowering, respectively. Accordingly, TCP8 mutant plants showed a delay in the maximum expression of FT and reduced SOC1 transcript levels, while plants overexpressing TCP8 presented increased transcript levels of both genes. Notably, the related class I protein TCP23 showed the opposite behavior, since TCP23 mutation and overexpression accelerated and retarded flowering, respectively. To elucidate the molecular basis of these differences, we analyzed TCP8 and TCP23 comparatively. We found that both proteins are able to physically interact and bind class I TCP motifs, but only TCP8 shows transcriptional activation activity when expressed in plants, which is negatively affected by TCP23. From the analysis of plants expressing different chimeras between the TCPs, we found that the N-terminal region located upstream of the TCP domain is responsible for the opposite effect that TCP8 and TCP23 exert over flowering time and regulation of FT and SOC1 expression. These results suggest that structural features outside the TCP domain modulate the specificity of action of class I TCPs.

SHINE clade of ERF transcription factors: A significant player in abiotic and biotic stress tolerance in plants

SHINE (SHN) clade transcription factors (TFs) represents a subfamily of APETALA2/ethylene-responsive factor (AP2/ERF) proteins. The latter, is characterized by its responsiveness to the phytohormone ethylene and the presence of AP2 DNA-binding domain. They are involved in many biological processes and in responses to different environmental constraints. SHN TFs were among the first identified regulators of cuticle formation. Cuticle plays crucial role in plant tolerance to drought, salinity and high temperature as well as in defense against pathogens. In addition, SHN were shown to be involved in the regulation of stomatal development which influences resistance to drought and diseases. Interestingly, recent studies have also shown that SHN TFs are involved in mediating the beneficial effects of arbuscular mycorrhizal fungi (AMF) as well as disease resistance conferred by nanoparticles. To fulfill their roles, SHN TFs are controlled upstream by other TFs and they control, in their turn, different downstream genes. In this review, we highlight the role of SHN TFs in different abiotic and biotic stresses through their involvement in cuticle biosynthesis, stomatal development and molecular regulation of biochemical and physiological traits. In addition, we discuss the regulation of SHN TFs by plant hormones and their influence on hormone biosynthesis and signaling pathways. Knowledge of this complex regulation can be put into contribution to increase multiple abiotic stress tolerances through transgenesis, gene editing and classical breeding.

Where whole-genome duplication is most beneficial: Adaptation of mangroves to a wide salinity range between land and sea

Whole-genome duplication (WGD) is believed to increase the chance of adaptation to a new environment. This conjecture may apply particularly well to new environments that are not only different but also more variable than ancestral habitats. One such prominent environment is the interface between land and sea, which has been invaded by woody plants, collectively referred as mangroves, multiple times. Here, we use two distantly related mangrove species (Avicennia marina and Rhizophora apiculata) to explore the effects of WGD on the adaptive process. We found that a high proportion of duplicated genes retained after WGD have acquired derived differential expression in response to salt gradient treatment. The WGD duplicates differentially expressed in at least one copy usually (>90%) diverge from their paralogues' expression profiles. Furthermore, both species evolved in parallel to have one paralogue expressed at a high level in both fresh water and hypersaline conditions but at a lower level at medium salinity. The pattern contrasts with the conventional view of monotone increase/decrease as salinity increases. Differentially expressed copies have thus probably acquired a new role in salinity tolerance. Our results indicate that the WGD duplicates may have evolved to function collaboratively in coping with different salinity levels, rather than specializing in the intermediate salinity optimal for mangrove plants. In conclusion, WGD and the retained duplicates appear to be an effective solution for adaptation to new and unstable environments.

More than growth: Phytohormone-regulated transcription factors controlling plant immunity, plant development and plant architecture

Activation of immunity by exogenous signals or mutations leading to autoimmunity has long been associated with decreased plant growth, known as the growth-defense tradeoff. Originally thought to be a redirection of metabolic resources towards defense and away from growth, recent studies have demonstrated that growth and defense can be uncoupled, indicating that metabolic regulation is not solely responsible for the growth-defense tradeoff. Immunity activation has effects on plant development beyond the reduction of plant biomass, including changes in plant architecture. Phytohormone signaling pathways, and crosstalk between these pathways, are responsible for regulating plant growth and development, and plant defense responses. Here we review the hormonal regulation of transcription factors that play roles in both defense and development, with a focus on their effects on plant architecture, and suggest the targeting of these transcription factors to increase plant immunity and change plant growth and form for enhancement of agronomical traits.

Evolutionary analyses and expression patterns of TCP genes in Ranunculales

TCP transcription factors play a role in a large number of developmental processes and are at the crossroads of numerous hormonal biosynthetic and signaling pathways. The complete repertoire of TCP genes has already been characterized in several plant species, but not in any species of early diverging eudicots. We focused on the order Ranunculales because of its phylogenetic position as sister group to all other eudicots and its important morphological diversity. Results show that all the TCP genes expressed in the floral transcriptome of Nigella damascena (Ranunculaceae) are the orthologs of the TCP genes previously identified from the fully sequenced genome of Aquilegia coerulea. Phylogenetic analyses combined with the identification of conserved amino acid motifs suggest that six paralogous genes of class I TCP transcription factors were present in the common ancestor of angiosperms. We highlight independent duplications in core eudicots and Ranunculales within the class I and class II subfamilies, resulting in different numbers of paralogs within the main subclasses of TCP genes. This has most probably major consequences on the functional diversification of these genes in different plant clades. The expression patterns of TCP genes in Nigella damascena were consistent with the general suggestion that CIN and class I TCP genes may have redundant roles or take part in same pathways, while CYC/TB1 genes have more specific actions. Our findings open the way for future studies at the tissue level, and for investigating redundancy and subfunctionalisation in TCP genes and their role in the evolution of morphological novelties.

StTCP15 regulates potato tuber sprouting by modulating the dynamic balance between abscisic acid and gibberellic acid

The major stages of the potato life cycle are tuber dormancy and sprouting, however, there is still known very little of the mechanisms that control these processes. TCP (Theosinte branch I, Cycloidea, proliferationcell factors 1 and 2) transcription factors play a key role in plant growth and dormancy related developmental processes. Previous researches demonstrated that TCP transcription factor StTCP15 had a function in the promotion of dormancy. To elucidate the function of StTCP15 gene, it was cloned from potato cultivar "Desiree," which encodes a polypeptide consisting of 414 amino acids and is mainly found in the nucleus. The potato tubers of StTCP15 overexpression lines sprouted in advance, while the potato tubers of StTCP15 down-regulated expression lines showed delayed sprouting. In addition, it was also found that overexpression lines of StTCP15 extremely significantly reduced the ratio of abscisic acid (ABA)/gibberellic acid (GA₃), while the superoxide dismutase activity decreased, and the activity of peroxidase and catalase increased compared with the wild type. The opposite result was found in the down-regulated expression lines of StTCP15 gene. Three interacting proteins, StSnRK1, StF-Box and StGID1, were screened by Yeast two-hybrid, and verified by Bimolecular Fluorescence Complementation and Split-luciferase, indicating that StTCP15 could affect ABA and GA₃ signaling pathways to regulate potato tuber dormancy and sprouting. Together, these results demonstrated that StTCP15 regulated potato tuber dormancy and sprouting by affecting the dynamic balance between ABA and GA₃. The result could provide some information on the molecular mechanism of StTCP15 regulating potato tuber dormancy and sprouting.

TCP15 interacts with GOLDEN2-LIKE 1 to control cotyledon opening in Arabidopsis

After germination, exposure to light promotes the opening and expansion of the cotyledons and the development of the photosynthetic apparatus in a process called de-etiolation. This process is crucial for seedling establishment and photoautotrophic growth. TEOSINTE BRANCHED 1, CYCLOIDEA, and PROLIFERATING CELL FACTORS (TCP) transcription factors are important developmental regulators of plant responses to internal and external signals that are grouped into two main classes. In this study, we identified GOLDEN2-LIKE 1 (GLK1), a key transcriptional regulator of photomorphogenesis, as a protein partner of class I TCPs during light-induced cotyledon opening and expansion in Arabidopsis. The class I TCP TCP15 and GLK1 are mutually required for cotyledon opening and the induction of SAUR and EXPANSIN genes, involved in cell expansion. TCP15 also participates in the expression of photosynthesis-associated genes regulated by GLK1, like LHCB1.4 and LHCB2.2. Furthermore, GLK1 and TCP15 bind to the same promoter regions of different target genes containing either GLK or TCP binding motifs and binding of TCP15 is affected in a GLK1-deficient background, suggesting that a complex between TCP15 and GLK1 participates in the induction of these genes. We postulate that GLK1 helps to recruit TCP15 for the modulation of cell expansion genes in cotyledons and that the functional interaction between these transcription factors may serve to coordinate the expression of cell expansion genes with that of genes involved in the development of the photosynthetic apparatus.

Characterization of the TCP Gene Family in Chrysanthemum nankingense and the Role of CnTCP4 in Cold Tolerance

Plant-specific TCP transcription factors play a key role in plant development and stress responses. Chrysanthemum nankingense shows higher cold tolerance than its ornamental polyploid counterpart. However, whether the TCP gene family plays a role in conferring cold tolerance upon C. nankingense remains unknown. Here, we identified 23 CnTCP genes in C. nankingense, systematically analyzed their phylogenetic relationships and synteny with TCPs from other species, and evaluated their expression profiles at low temperature. Phylogenetic analysis of the protein sequences suggested that CnTCP proteins fall into two classes and three clades, with a typical bHLH domain. However, differences between C. nankingense and Arabidopsis in predicted protein structure and binding sites suggested a unique function of CnTCPs in C. nankingense. Furthermore, expression profiles showed that expression of most CnTCPs were downregulated under cold conditions, suggesting their importance in plant responses to cold stress. Notably, expression of miR319 and of its predicted target genes, CnTCP2/4/14, led to fast responses to cold. Overexpression of Arabidopsis CnTCP4 led to hypersensitivity to cold, suggesting that CnTCP4 might play a negative role in C. nankingense responses to cold stress. Our results provide a foundation for future functional genomic studies on this gene family in chrysanthemum.

Hormone and carbohydrate metabolism associated genes play important roles in rhizome bud full-year germination of Cephalostachyum pingbianense

Cephalostachyum pingbianense is the only woody bamboo species that can produce bamboo shoots in four seasons under natural conditions. So far, the regulatory mechanism of shoot bud differentiation and development is unknown. In the present study, indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellin A3 (GA₃ ) and abscisic acid (ABA) contents determination, RNA sequencing and differentially expressed gene analysis were performed on dormant rhizome bud (DR), growing rhizome bud (GR), and germinative bud (GB) in each season. The results showed that the contents of IAA and ZR increased while ABA content decreased, and GA₃ content was stable during bud transition from dormancy to germination in each season. Moreover, rhizome bud germination was cooperatively regulated by multiple pathways such as carbohydrate metabolism, hormone signal transduction, cell wall biogenesis, temperature response, and water transport. The inferred hub genes among these candidates were identified by protein-protein interaction network analyses, most of which were involved in hormone and carbohydrate metabolism, such as HK and BGLU4 in spring, IDH and GH3 in winter, GPI and talA/talB in summer and autumn. It is speculated that dynamic phytohormone changes and differential expression of these genes promote the release of rhizome bud dormancy and contribute to the phenological characteristics of full-year shooting. Moreover, the rhizome buds of C. pingbianense may not suffer from ecodormancy in winter. These findings would help accumulate knowledge on shooting mechanisms in woody bamboos and provide a physiological insight into germplasm conservation and forest management of C. pingbianense.

Subtle interplay between trichome development and cuticle formation in plants

Trichomes and cuticles are key protective epidermal specializations. This review highlights the genetic interplay existing between trichome and cuticle formation in a variety of species. Controlling trichome development, the biosynthesis of trichome-derived specialized metabolites as well as cuticle biosynthesis and deposition can be viewed as different aspects of a common defensive strategy adopted by plants to protect themselves from environmental stresses. Existence of such interplay is based on the mining of published transcriptomic data as well as on phenotypic observations in trichome or cuticle mutants where the morphology of both structures often appear to be concomitantly altered. Given the existence of several trichome developmental pathways depending on the plant species and the types of trichomes, genetic interactions between cuticle formation and trichome development are complex to decipher and not easy to generalize. Based on our review of the literature, a schematic overview of the gene network mediating this transcriptional interplay is presented for two model plant species: Arabidopsis thaliana and Solanum lycopersicum. In addition to fundamental new insights on the regulation of these processes, identifying key transcriptional switches controlling both processes could also facilitate more applied investigations aiming at improving much desired agronomical traits in plants.

WHIRLY1 functions in the nucleus to regulate barley leaf development and associated metabolite profiles

The WHIRLY (WHY) DNA/RNA binding proteins fulfil multiple but poorly characterised functions in leaf development. Here, we show that WHY1 transcript levels were highest in the bases of 7-day old barley leaves. Immunogold labelling revealed that the WHY1 protein was more abundant in the nuclei than the proplastids of the leaf bases. To identify transcripts associated with leaf development we conducted hierarchical clustering of differentially abundant transcripts along the developmental gradient of wild-type leaves. Similarly, metabolite profiling was employed to identify metabolites exhibiting a developmental gradient. A comparative analysis of transcripts and metabolites in barley lines (W1–1 and W1–7) lacking WHY1, which show delayed greening compared with the wild type revealed that the transcript profile of leaf development was largely unchanged in W1–1 and W1–7 leaves. However, there were differences in levels of several transcripts encoding transcription factors associated with chloroplast development. These include a barley homologue of the Arabidopsis GATA transcription factor that regulates stomatal development, greening and chloroplast development, NAC1; two transcripts with similarity to Arabidopsis GLK1 and two transcripts encoding ARF transcriptions factors with functions in leaf morphogenesis and development. Chloroplast proteins were less abundant in the W1–1 and W1–7 leaves than the wild type. The levels of tricarboxylic acid cycle metabolites and GABA were significantly lower in WHY1 knockdown leaves than the wild type. This study provides evidence that WHY1 is localised in the nuclei of leaf bases, contributing the regulation of nuclear-encoded transcripts that regulate chloroplast development.

Arabidopsis thaliana TCP15 interacts with the MIXTA-like transcription factor MYB106/NOECK

MYB106 and MYB16 are MIXTA-like transcription factors that control trichome maturation and cuticle formation in Arabidopsis. In a recent study, we found that the TEOSINTE BRANCHED 1, CYCLOIDEA and PROLIFERATING CELL FACTORS (TCP) transcription factor TCP15 also acts as an important regulator of aerial epidermis specialization in Arabidopsis through the control of trichome development and cuticle formation. TCP15 and MYB106 regulate the expression of common groups of genes, including genes coding for transcription factors and enzymes of the cuticle biosynthesis pathway. In this study, we report that TCP15 physically interacts with MYB106 when both proteins are expressed in yeast cells or Nicotiana bentamiana leaves. Furthermore, we also observed interaction in leaves of Arabidopsis thaliana. Altogether, our findings raise the possibility that TCP15 and MYB106 bind together to the promoters of target genes to exert their action. Our data provide a base to investigate the role of TCP-MIXTA complexes in the context of cuticle development in Arabidopsis thaliana.

A Class II TCP Transcription Factor PaTCP4 from Platanus acerifolia Regulates Trichome Formation in Arabidopsis

London plane tree is widely grown as a landscaping and street tree, but the release of its trichomes creates a serious air-borne pollution problem. Identifying the key genes that regulate the development of trichomes is, therefore, an important tool for the molecular breeding of Platanus acerifolia. In this study, a sequence homologous with the Arabidopsis Class II TCP subfamily was identified from London plane, and named PaTCP4. The expression of PaTCP4 was detected in various organs of London plane trees, significantly in the trichomes. Overexpression of PaTCP4 in Arabidopsis reduced the trichome density on the first pair of true leaves, and atypical 5-branched trichomes were also detected on those leaves. The expression of endogenous AtCPC and AtTCL2 was significantly increased in PaTCP4 transgenic lines, and was associated with a decrease in the expression of endogenous AtGL2. Furthermore, the expression of endogenous AtGL3 was significantly increased. In addition, the protein product of PaTCP4 was shown to directly activate AtCPC, AtTCL2, AtGL3, AtGIS, PaGIS, and PaGL3 in yeast one-hybrid assays and in the dual-luciferase reporter system. Taken together, these results identify a role for PaTCP4 in trichome initiation and branching in Arabidopsis. Thus, PaTCP4 represents a strong candidate gene for regulating the development of trichomes in London plane trees.

HOMEODOMAIN PROTEIN8 mediates jasmonate-triggered trichome elongation in tomato

Plant hormones can adjust the physiology and development of plants to enhance their adaptation to biotic and abiotic challenges. Jasmonic acid (JA), one of the immunity hormones in plants, triggers genome-wide transcriptional changes in response to insect attack and wounding. Although JA is known to affect the development of trichomes, epidermal appendages that form a protective barrier against various stresses, it remains unclear how JA interacts with developmental programs that regulate trichome development. In this study, we show that JA affects trichome length in tomato by releasing the transcriptional repression mediated by Jasmonate ZIM (JAZ) proteins. We identified SlJAZ4, a negative regulator preferentially expressed in trichomes, as the critical component in JA signaling in tomato trichomes. We also identified a homeodomain-leucine zipper gene, SlHD8, as the downstream regulator of JA signaling that promotes trichome elongation. SlHD8 is also highly expressed in trichomes and physically interacts with SlJAZ4. Loss-of-function mutations in SlHD8 caused shorter trichomes, a phenotype that was only partially rescued by methyl jasmonate treatment. Our dual-luciferase and chromatin immunoprecipitation-quantitative PCR assays revealed that SlHD8 regulates trichome elongation by directly binding to the promoters of a set of cell-wall-loosening protein genes and activating their transcription. Together, our findings define SlHD8-SlJAZ4 as a key module mediating JA-induced trichome elongation in tomato.

Genome-Wide Identification and Characterization of the TCP Gene Family in Cucumber (Cucumis sativus L.) and Their Transcriptional Responses to Different Treatments

TCP proteins are plant-specific transcription factors widely implicated in leaf morphogenesis and senescence, flowering, lateral branching, hormone crosstalk, and stress responses. However, the relationship between the transcription pattern of TCPs and organ development in cucumber has not been systematically studied. In this study, we performed a genome-wide identification of putative TCP genes and analyzed their chromosomal location, gene structure, conserved motif, and transcript expression. A total of 27 putative TCP genes were identified and characterized in cucumber. All 27 putative CsTCP genes were classified into class I and class II. Class I comprised 12 CsTCPs and Class II contained 15 CsTCPs. The 27 putative CsTCP genes were randomly distributed in five of seven chromosomes in cucumber. Four putative CsTCP genes were found to contain putative miR319 target sites. Quantitative RT-PCR revealed that 27 putative CsTCP genes exhibited different expression patterns in cucumber tissues and floral organ development. Transcript expression and phenotype analysis showed that the putative CsTCP genes responded to temperature and photoperiod and were induced by gibberellin (GA)and ethylene treatment, which suggested that CsTCP genes may regulate the lateral branching by involving in multiple signal pathways. These results lay the foundation for studying the function of cucumber TCP genes in the future.