ERF4 interacts with and antagonizes TCP15 in regulating endoreduplication and cell growth in Arabidopsis.

Endoreduplication is prevalent during plant growth and development, and is often correlated with large cell and organ size. Despite its prevalence, the transcriptional regulatory mechanisms underlying the transition from mitotic cell division to endoreduplication remain elusive. Here, we characterize ETHYLENE-RESPONSIVE ELEMENT BINDING FACTOR 4 (ERF4) as a positive regulator of endoreduplication through its function as a transcriptional repressor. ERF4 was specifically expressed in mature tissues in which the cells were undergoing expansion, but was rarely expressed in young organs. Plants overexpressing ERF4 exhibited much larger cells and organs, while plants that lacked functional ERF4 displayed smaller organs than the wild-type. ERF4 was further shown to regulate cell size by controlling the endopolyploidy level in the nuclei. Moreover, ERF4 physically associates with the class I TEOSINTE BRANCHED 1/CYCLOIDEA/PCF (TCP) protein TCP15, a transcription factor that inhibits endoreduplication by activating the expression of a key cell-cycle gene, CYCLIN A2;3 (CYCA2;3). A molecular and genetic analysis revealed that ERF4 promotes endoreduplication by directly suppressing the expression of CYCA2;3. Together, this study demonstrates that ERF4 and TCP15 function as a module to antagonistically regulate each other's activity in regulating downstream genes, thereby controlling the switch from the mitotic cell cycle to endoreduplication during leaf development. These findings expand our understanding of how the control of the cell cycle is fine-tuned by an ERF4-TCP15 transcriptional complex.

Genome-wide identification of the tobacco GDSL family and apical meristem-specific expression conferred by the GDSL promoter.

BACKGROUND: GDSL esterases/lipases are a large protein subfamily defined by the distinct GDSL motif, and play important roles in plant development and stress responses. However, few studies have reported on the role of GDSLs in the growth and development of axillary buds. This work aims to identify the GDSL family members in tobacco and explore whether the NtGDSL gene contributes to development of the axillary bud in tobacco. RESULTS: One hundred fifty-nine GDSL esterase/lipase genes from cultivated tobacco (Nicotiana tabacum) were identified, and the dynamic changes in the expression levels of 93 of these genes in response to topping, as assessed using transcriptome data of topping-induced axillary shoots, were analysed. In total, 13 GDSL esterase/lipase genes responded with changes in expression level. To identify genes and promoters that drive the tissue-specific expression in tobacco apical and axillary buds, the expression patterns of these 13 genes were verified using qRT-PCR. GUS activity and a lethal gene expression pattern driven by the NtGDSL127 promoter in transgenic tobacco demonstrated that NtGDSL127 is specifically expressed in apical buds, axillary buds, and flowers. Three separate deletions in the NtGDSL127 promoter demonstrated that a minimum upstream segment of 235 bp from the translation start site can drive the tissue-specific expression in the apical meristem. Additionally, NtGDSL127 responded to phytohormones, providing strategies for improving tobacco breeding and growth. CONCLUSION: We propose that in tobacco, the NtGDSL127 promoter directs expression specifically in the apical meristem and that expression is closely correlated with axillary bud development.

Genome-wide identification of the ARRs gene family in tobacco (Nicotiana tabacum).

BACKGROUND: The growth of axillary buds determines the shoot branching and morphology of plants, and its initiation and development are regulated by a series of hormonal signals, such as cytokinin. Arabidopsis response regulators (ARRs) can regulate the growth and development, disease resistance and stress resistance of plants by participating in cytokinin signaling. OBJECTIVE: To explore the distribution and expression pattern of ARR members in tobacco. METHODS: The identification, isoelectric points, molecular weights, protein subcellular localization prediction, multiple sequence alignment, phylogenetic analysis, protein motifs and structures, chromosome distributions of deduced ARR proteins were conducted. The gene expression profiling of various tissues in response to topping, low temperature and drought were analyzed by RNA-seq and qRT-PCR. RESULTS: 59 ARR genes from cultivated tobacco (Nicotiana tabacum) were identified, namely NtARRs, including 21 type A NtARRs and 38 type B NtARRs. The 59 NtARRs were expressed mainly in all organs except the fruits. Some representative NtARRs may participate in axillary bud initiation and development, as well as in stress resistance through cytokinin signal transduction. CONCLUSION: Understanding the roles of NtARRs in the molecular mechanisms responsible for axillary bud growth and stress tolerance could aid in targeted breeding in crops.

Control of axillary bud growth in tobacco through toxin gene expression system.

The control of axillary bud development after removing the terminal buds (topping) of plants is a research hotspot, and the control of gene expression, like switching on and off, allows us to further study biological traits of interest, such as plant branching and fertility. In this study, a toxin gene control system for plants based on dexamethasone (DEX) induction was constructed, and the positive transgenic tobacco exhibited growth retardation in the application area (axillary bud). The expression level of the lethal Diphtheria toxin A (DTA) gene under different DEX concentrations at different application days was analyzed. The highest expression levels appeared at 5 days after the leaf injection of DEX. The DTA transcripts were induced by 5 µM DEX and peaked in response to 50 µM DEX at 5 days after leaf injection. Here, a chemical induction system, combined with a toxin gene, were used to successfully control the growth of tobacco axillary buds after topping. The DTA expression system under DEX induction was sensitive and efficient, therefore, can be used to control axillary bud growth and development in tobacco.

Induction of Male Sterility in Tobacco by Anther-Specific Expression of the Gene for Ricin Enzymatic Subunit A Chain RTA.

Targeted gene expression in plants allows us to further study biological traits of interest, such as reproductive and developmental processes. Here, the tobacco TA29 anther-specific promoter was used to direct the expression of the ricin enzymatic subunit A (RTA) in transgenic tobacco plants, phenotypic analysis of the resulting positive transgenic tobacco (Nicotiana tabacum L.) plants demonstrated that RTA expression led to a reduction in pistil length and shriveling of anthers, as well as the grayish-brown color of anthers, the reduced pollen viability and male sterility. For the first time, a plant-derived ricin gene enzymatic subunit A (RTA) expression system under the tissue-specific promoter was demonstrated to be sensitive and efficient in controlling plant sterility and creating male-sterile materials. Consequently, it could be used to control other agronomic traits and produce hybrid seeds in plants in the future.