The floral repressors TEMPRANILLO1 and 2 modulate salt tolerance by regulating hormonal components and photo-protection in Arabidopsis

Flavin-containing monooxygenases FMOGS-OXs integrate flowering transition and salt tolerance in Arabidopsis thaliana

Salt stress substantially leads to flowering delay. The regulation of salt-induced late flowering has been studied at the transcriptional and protein levels; however, the involvement of secondary metabolites has rarely been investigated. Here, we report that FMOGS-OXs (EC 1.14.13.237), the enzymes that catalyze the biosynthesis of glucosinolates (GSLs), promote flowering transition in Arabidopsis thaliana. It has been reported that WRKY75 is a positive regulator, and MAF4 is a negative regulator of flowering transition. The products of FMOGS-OXs, methylsulfinylalkyl GSLs (MS GSLs), facilitate flowering by inducing WRKY75 and repressing the MAS-MAF4 module. We further show that the degradation of MS GSLs is involved in salt-induced late flowering and salt tolerance. Salt stress induces the expression of myrosinase genes, resulting in the degradation of MS GSLs, thereby relieving the promotion of WRKY75 and inhibition of MAF4, leading to delayed flowering. In addition, the degradation products derived from MS GSLs enhance salt tolerance. Previous studies have revealed that FMOGS-OXs exhibit alternative catalytic activity to form trimethylamine N-oxide (TMAO) under salt stress, which activates multiple stress-related genes to promote salt tolerance. Therefore, FMOGS-OXs integrate flowering transition and salt tolerance in various ways. Our study shed light on the functional diversity of GSLs and established a connection between flowering transition, salt resistance, and GSL metabolism.

SmRAV1, an AP2 and B3 Transcription Factor, Positively Regulates Eggplant's Response to Salt Stress

Salt stress is a lethal abiotic stress threatening global food security on a consistent basis. In this study, we identified an AP2 and B3 domain-containing transcription factor (TF) named SmRAV1, and its expression levels were significantly up-regulated by NaCl, abscisic acid (ABA), and hydrogen peroxide (H2O2) treatment. High expression of SmRAV1 was observed in the roots and sepal of mature plants. The transient expression assay in Nicotiana benthamiana leaves revealed that SmRAV1 was localized in the nucleus. Silencing of SmRAV1 via virus-induced gene silencing (VIGS) decreased the tolerance of eggplant to salt stress. Significant down-regulation of salt stress marker genes, including SmGSTU10 and SmNCED1, was observed. Additionally, increased H2O2 content and decreased catalase (CAT) enzyme activity were recorded in the SmRAV1-silenced plants compared to the TRV:00 plants. Our findings elucidate the functions of SmRAV1 and provide opportunities for generating salt-tolerant lines of eggplant.

Transcriptomic and hormonal analysis of the roots of maize seedlings grown hydroponically at low temperature

Prolonged cold stress has a strong effect on plant growth and development, especially in subtropical crops such as maize. Soil temperature limits primary root elongation, mainly during early seedling establishment. However, little is known about how moderate temperature fluctuations affect root growth at the molecular and physiological levels. We have studied root tips of young maize seedlings grown hydroponically at 30 ºC and after a short period (up to 24 h) of moderate cooling (20 ºC). We found that both cell division and cell elongation in the root apical meristem are affected by temperature. Time-course analyses of hormonal and transcriptomic profiles were achieved after temperature reduction from 30 ºC to 20 ºC. Our results highlighted a complex regulation of endogenous pathways leading to adaptive root responses to moderate cooling conditions.

NtRAV4 negatively regulates drought tolerance in Nicotiana tabacum by enhancing antioxidant capacity and defence system

KEY MESSAGE

NtRAV4 is a nucleus-localised protein and no self-activation effect. ntrav4 mutants maintain the steady state of the ROS system under drought stress by enhancing antioxidant capacity and defence system. The APETALA2/ethylene response factor (AP2/ERF) transcription factor (TF) family plays an important role in plant responses to environmental stresses. In this study, we identified a novel NtRAV4 TF, a member of RAV subfamily among AP2/ERF gene family, which have AP2 and B3 domain in its N- and C-terminus, respectively. Subcellular localisation and self-activation activity analysis revealed that NtRAV4 localised in the nucleus and had no self-activation effect. The overexpression and gene editing vectors of NtRAV4 were constructed by homologous recombination and CRISPR/Cas9 gene editing methods, and transformed into tobacco by agrobacterium-mediated method. ntrav4 led to the appearance of termination codon in advance and lacked the unique B3 domain of RAV subfamily protein. Further analysis displayed that knockout of the NtRAV4 in tobacco increased drought tolerance with high relative water content, accompanied by reduced stomatal aperture, density, and stomatal opening ratio compared to overexpression lines and WT. Moreover, ntrav4 knockout plants also exhibited increased osmotic tolerance with low malondialdehyde (MDA) and ion leakage (EL), less accumulation of O2•- and H2O2, and high enzymatic antioxidant (SOD, POD, CAT) activities, non-enzymatic antioxidant (AsA-GSH cycle) contents and hormone (IAA, ABA, GA3, and ZR) levels under drought stress. Furthermore, ntrav4 mutants in tobacco improved the expression levels of ROS-related proline synthesis and stress-responsive genes under osmotic stress. Our results indicate that NtRAV4 negatively regulates plant tolerance to drought stress by reducing water loss and activating the antioxidant system and stress-related gene expression to maintain the steady state of the ROS system.

Genome-wide characterization and expression analysis of AP2/ERF genes in eggplant (Solanum melongena L.)

The AP2/ERF (APETALA2/Ethylene Response Factor) transcription factor superfamily plays crucial roles in a slew of physiological processes, such as plant growth and development, stress response, and secondary metabolites biosynthesis. Eggplant, especially the one rich with anthocyanins, is an economically important horticultural vegetable cultivated worldwide. In this study, we comprehensively analyzed the putative AP2/ERF gene family members and their response to abiotic stress in eggplant. As per the phylogenetic, conserved domains, and motif analysis, 178 AP2/ERF genes in this study belonged to five subfamilies. Chromosomal distributions analysis elucidated stochastic distribution of 178 putative SmAP2/ERF genes across the twelve chromosomes of eggplant. Expression profiles of sixteen selected AP2/ERF genes response to low temperature, drought, salt, abscisic acid, and ethylene treatments were analyzed, which revealed the involvement of SmAP2/ERF genes in diverse signaling pathways. In addition, we integrated RNA-Seq data on anthocyanin biosynthesis in eggplant with yeast one-hybrid and dual-luciferase assays and identified involvement of the SmAP2/ERF genes (Smechr0902114.1 and Smechr1102075.1) in the regulation of anthocyanin biosynthesis. This study will enable further functional characterization of AP2/ERF genes in eggplant and extend the current understanding of the role played by AP2/ERF genes in anthocyanin biosynthesis regulation.

Transcriptomic Analysis for the Identification of Metabolic Pathway Genes Related to Toluene Response in Ardisia pusilla

Toluene is an industrial raw material and solvent that can be found abundantly in our daily life products. The amount of toluene vapor is one of the most important measurements for evaluating air quality. The evaluation of toluene scavenging ability of different plants has been reported, but the mechanism of plant response to toluene is only partially understood. In this study, we performed RNA sequencing (RNA-seq) analysis to detect differential gene expression in toluene-treated and untreated leaves of Ardisiapusilla. A total of 88,444 unigenes were identified by RNA-seq analysis, of which 49,623 were successfully annotated and 4101 were differentially expressed. Gene ontology analysis revealed several subcategories of genes related to toluene response, including cell part, cellular process, organelle, and metabolic processes. We mapped the main metabolic pathways of genes related to toluene response and found that the differentially expressed genes were mainly involved in glycolysis/gluconeogenesis, starch and sucrose metabolism, glycerophospholipid metabolism, carotenoid biosynthesis, phenylpropanoid biosynthesis, and flavonoid biosynthesis. In addition, 53 transcription factors belonging to 13 transcription factor families were identified. We verified 10 differentially expressed genes related to metabolic pathways using quantitative real-time PCR and found that the results of RNA-seq were positively correlated with them, indicating that the transcriptome data were reliable. This study provides insights into the metabolic pathways involved in toluene response in plants.

Isoprenoid-Derived Metabolites and Sugars in the Regulation of Flowering Time: Does Day Length Matter?

In plants, a diverse set of pathways regulate the transition to flowering, leading to remarkable developmental flexibility. Although the importance of photoperiod in the regulation of flowering time is well known, increasing evidence suggests the existence of crosstalk among the flowering pathways regulated by photoperiod and metabolic pathways. For example, isoprenoid-derived phytohormones (abscisic acid, gibberellins, brassinosteroids, and cytokinins) play important roles in regulating flowering time. Moreover, emerging evidence reveals that other metabolites, such as chlorophylls and carotenoids, as well as sugar metabolism and sugar accumulation, also affect flowering time. In this review, we summarize recent findings on the roles of isoprenoid-derived metabolites and sugars in the regulation of flowering time and how day length affects these factors.

EjRAV1/2 Delay Flowering Through Transcriptional Repression of EjFTs and EjSOC1s in Loquat

Most species in Rosaceae usually need to undergo several years of juvenile phase before the initiation of flowering. After 4-6 years' juvenile phase, cultivated loquat (Eriobotrya japonica), a species in Rosaceae, enters the reproductive phase, blooms in the autumn and sets fruits during the winter. However, the mechanisms of the transition from a seedling to an adult tree remain obscure in loquat. The regulation networks controlling seasonal flowering are also largely unknown. Here, we report two RELATED TO ABI3 AND VP1 (RAV) homologs controlling juvenility and seasonal flowering in loquat. The expressions of EjRAV1/2 were relatively high during the juvenile or vegetative phase and low at the adult or reproductive phase. Overexpression of the two EjRAVs in Arabidopsis prolonged (about threefold) the juvenile period by repressing the expressions of flowering activator genes. Additionally, the transformed plants produced more lateral branches than the wild type plants. Molecular assays revealed that the nucleus localized EjRAVs could bind to the CAACA motif of the promoters of flower signal integrators, EjFT1/2, to repress their expression levels. These findings suggest that EjRAVs play critical roles in maintaining juvenility and repressing flower initiation in the early life cycle of loquat as well as in regulating seasonal flowering. Results from this study not only shed light on the control and maintenance of the juvenile phase, but also provided potential targets for manipulation of flowering time and accelerated breeding in loquat.