LeMYC2 acts as a negative regulator of blue light mediated photomorphogenic growth, and promotes the growth of adult tomato plants

Tomato B-cell lymphoma2 (Bcl2)-associated athanogene 5 (SlBAG5) contributes negatively to immunity against necrotrophic fungus Botrytis cinerea through interacting with SlBAP1 and modulating catalase activity

The evolutionarily conserved and multifunctional B-cell lymphoma2 (Bcl2)-associated athanogene proteins (BAGs), serving as co-chaperone regulators, play a pivotal role in orchestrating plant stress responses. In this study, the possible involvement of tomato SlBAG genes in resistance to Botrytis cinerea was examined. The SlBAG genes respond with different expression change patterns to B. cinerea and defense signaling hormones. SlBAG proteins are individually differentially localized to the nucleus, mitochondria, cytoplasm, endoplasmic reticulum (ER), or vacuole. Silencing of SlBAG5 enhanced immunity to B. cinerea, while overexpression weakened it, affecting Botrytis-induced JA/ET defense gene expression and JA levels. Chitin-induced ROS burst and expression of PTI marker genes SlPTI5 and SlLRR22 were strengthened in SlBAG5-silenced plants but were weakened in SlBAG5-overexpressing plants (SlBAG5-OE) plants. SlBAG5 interacts with BON1 ASSOCIATED PROTEIN 1 (SlBAP1) through its BAG domain, and the stability of SlBAP1 depends on the presence of SlBAG5. Silencing of SlBAP1 conferred increased resistance to B. cinerea through increased expression of JA/ET signaling and defense genes. SlBAP1 functions by recruiting and boosting SlCAT3 activity to remove H2O2. The findings suggest that SlBAG5 suppresses tomato immunity to B. cinerea by stabilizing SlBAP1, which modulates ROS scavenging and acts as a negative regulator of immunity.

SlUPA-like, a bHLH Transcription Factor in Tomato (Solanum lycopersicum), Serves as the Crosstalk of GA, JA and BR

The bHLH (basic Helix-Loop-Helix) transcription factor serves as pivotal controller in plant growth and development. In a previous study, the overexpression of SlUPA-like in Solanum lycopersicum L. Ailsa Craig (AC++) altered the JA (Jasmonic acid) response and endogenous GA (Gibberellic acid) content. However, the detailed regulation mechanism was not fully explored. In the present research, we found that the overexpression of SlUPA-like influenced the accumulation of GA, JA and BR (Brassinolide). RNA-Seq data illustrated that the expression levels of genes related to these plant hormones were significantly affected. Additionally, the interaction of SlUPA-like with SlMYB21, SlMYC2 and SlDELLA was characterized by employing Y2H (Yeast Two-Hybrid) and BiFC (Bimolecular Fluorescence Complementation) assay. Furthermore, Dual-LUC (Dual-Luciferase) assay and EMSA (Electrophoretic Mobility Shift Assay) identified that SlUPA-like directly targeted the E-box motif in the promoter of SlGID2 and activated the transcription of SlGID2. These results shed light on the potential role of SlUPA-like in mediating crosstalk among multiple plant hormones and established a robust theoretical framework for further unraveling the functions of SlUPA-like transcription factors in the context of plant growth and hormone signal transduction.

CRISPR/Cas9-mediated knockout of NtMYC2a gene involved in resistance to bacterial wilt in tobacco

MYC2 is a class of bHLH family transcription factors and a major regulatory factor in the JA signaling pathway, and its molecular function in tobacco has not been reported. In this study, CRISPR/Cas9-mediated MYC2 gene NtMYC2a knockout mutants at tobacco was obtained and its agronomic traits, disease resistance, and chemical composition were identified. Comparing with the WT, the leaf width of the KO-NtMYC2a was narrowed, the nornicotine content and mecamylamine content increased significantly and the resistance to Ralstonia solanacearum significantly decreased. The transcriptome sequencing results showed that DEGs related to immunity, signal transduction and growth and development were enriched between KO-NtMYC2a and WT. NtJAR1 and NtCOI1 in KO-NtMYC2a were down-regulated to regulating the JA signaling pathway, result in a significant decrease in tobacco's resistance to R. solanacearum. Our research provides theoretical support for the functional research of MYC2 and the study of the mechanism of tobacco bacterial wilt resistance.

Comparative transcriptomic analysis of the nodulation-competent zone and inference of transcription regulatory network in silicon applied Glycine max [L.]-Merr. Roots

KEY MESSAGE

The study unveils Si's regulatory influence by regulating DEGs, TFs, and TRs. Further bHLH subfamily and auxin transporter pathway elucidates the mechanisms enhancing root development and nodulation. Soybean is a globally important crop serving as a primary source of vegetable protein for millions of individuals. The roots of these plants harbour essential nitrogen fixing structures called nodules. This study investigates the multifaceted impact of silicon (Si) application on soybean, with a focus on root development, and nodulation employing comprehensive transcriptomic analyses and gene regulatory network. RNA sequence analysis was utilised to examine the change in gene expression and identify the noteworthy differentially expressed genes (DEGs) linked to the enhancement of soybean root nodulation and root development. A set of 316 genes involved in diverse biological and molecular pathways are identified, with emphasis on transcription factors (TFs) and transcriptional regulators (TRs). The study uncovers TF and TR genes, categorized into 68 distinct families, highlighting the intricate regulatory landscape influenced by Si in soybeans. Upregulated most important bHLH subfamily and the involvement of the auxin transporter pathway underscore the molecular mechanisms contributing to enhanced root development and nodulation. The study bridges insights from other research, reinforcing Si's impact on stress-response pathways and phenylpropanoid biosynthesis crucial for nodulation. The study reveals significant alterations in gene expression patterns associated with cellular component functions, root development, and nodulation in response to Si.

Effects of Jasmonic Acid on Stress Response and Quality Formation in Vegetable Crops and Their Underlying Molecular Mechanisms

The plant hormone jasmonic acid plays an important role in plant growth and development, participating in many physiological processes, such as plant disease resistance, stress resistance, organ development, root growth, and flowering. With the improvement in living standards, people have higher requirements regarding the quality of vegetables. However, during the growth process of vegetables, they are often attacked by pests and diseases and undergo abiotic stresses, resulting in their growth restriction and decreases in their yield and quality. Therefore, people have found many ways to regulate the growth and quality of vegetable crops. In recent years, in addition to the role that JA plays in stress response and resistance, it has been found to have a regulatory effect on crop quality. Therefore, this study aims to review the jasmonic acid accumulation patterns during various physiological processes and its potential role in vegetable development and quality formation, as well as the underlying molecular mechanisms. The information provided in this manuscript sheds new light on the improvements in vegetable yield and quality.

SlMYC2 promotes SlLBD40-mediated cell expansion in tomato fruit development

As a plant-specific transcription factor, lateral organ boundaries domain (LBD) protein was reported to regulate plant growth and stress response, but the functional research of subfamily II genes is limited. SlMYC2, a master regulator of Jasmonic acid response, has been found to exhibit high expression levels in fruit and has been implicated in the regulation of fruit ripening and resistance to Botrytis. However, its role in fruit expansion remains unknown. In this study, we present evidence that a subfamily II member of LBD, namely SlLBD40, collaborates with SlMYC2 in the regulation of fruit expansion. Overexpression of SlLBD40 significantly promoted fruit growth by promoting mesocarp cell expansion, while knockout of SlLBD40 showed the opposite result. Similarly, SlMYC2 knockout resulted in a significant decrease in cell expansion within the fruit. Genetic analysis indicated that SlLBD40-mediated cell expansion depends on the expression of SlMYC2. SlLBD40 bound to the promoter of SlEXPA5, an expansin gene, but did not activate its expression directly. While, the co-expression of SlMYC2 and SlLBD40 significantly stimulated the activation of SlEXPA5, leading to an increase in fruit size. SlLBD40 interacted with SlMYC2 and enhanced the stability and abundance of SlMYC2. Furthermore, SlMYC2 directly targeted and activated the expression of SlLBD40, which is essential for SlLBD40-mediated fruit expansion. In summary, our research elucidates the role of the interaction between SlLBD40 and SlMYC2 in promoting cell expansion in tomato fruits, thus providing novel insights into the molecular genetics underlying fruit growth.

Overexpression of SlPRE3 alters the plant morphologies in Solanum lycopersicum

KEY MESSAGE

Overexpression of SlPRE3 is detrimental to the photosynthesis and alters plant morphology and root development. SlPRE3 interacts with SlAIF1/SlAIF2/SlPAR1/SlIBH1 to regulate cell expansion. Basic helix-loop-helix (bHLH) transcription factors play crucial roles as regulators in plant growth and development. In this study, we isolated and characterized SlPRE3, an atypical bHLH transcription factor gene. SlPRE3 exhibited predominant expression in the root and moderate expression in the senescent leaves. Comparative analysis with the wild type revealed significant differences in plant morphology in the 35S:SlPRE3 lines. These differences included increased internode length, rolling leaves with reduced chlorophyll accumulation, and elongated yet fewer adventitious roots. Additionally, 35S:SlPRE3 lines displayed elevated levels of GA3 (gibberellin A3) and reduced starch accumulation. Furthermore, utilizing the Y2H (Yeast two-hybrid) and the BiFC (Bimolecular Fluorescent Complimentary) techniques, we identified physical interactions between SlPRE3 and SlAIF1 (ATBS1-interacting factor 1)/SlAIF2 (ATBS1-interacting factor 2)/SlPAR1 (PHYTOCHROME RAPIDLY REGULATED 1)/SlIBH1 (ILI1-binding bHLH 1). RNA-seq analysis of root tissues revealed significant alterations in transcript levels of genes involved in gibberellin metabolism and signal transduction, cell expansion, and root development. In summary, our study sheds light on the crucial regulatory role of SlPRE3 in determining plant morphology and root development.

Exploring the metabolic basis of growth/defense trade-offs in complex environments with Nicotiana attenuata plants cosilenced in NaMYC2a/b expression

In response to challenges from herbivores and competitors, plants use fitness-limiting resources to produce (auto)toxic defenses. Jasmonate signaling, mediated by MYC2 transcription factors (TF), is thought to reconfigure metabolism to minimize these formal costs of defense and optimize fitness in complex environments. To study the context-dependence of this metabolic reconfiguration, we cosilenced NaMYC2a/b by RNAi in Nicotiana attenuata and phenotyped plants in the field and increasingly realistic glasshouse setups with competitors and mobile herbivores. NaMYC2a/b had normal phytohormonal responses, and higher growth and fitness in herbivore-reduced environments, but were devastated in high herbivore-load environments in the field due to diminished accumulations of specialized metabolites. In setups with competitors and mobile herbivores, irMYC2a/b plants had lower fitness than empty vector (EV) in single-genotype setups but increased fitness in mixed-genotype setups. Correlational analyses of metabolic, resistance, and growth traits revealed the expected defense/growth associations for most sectors of primary and specialized metabolism. Notable exceptions were some HGL-DTGs and phenolamides that differed between single-genotype and mixed-genotype setups, consistent with expectations of a blurred functional trichotomy of metabolites. MYC2 TFs mediate the reconfiguration of primary and specialized metabolic sectors to allow plants to optimize their fitness in complex environments.

Effects of High Voltage Electrical Discharge (HVED) on Endogenous Hormone and Polyphenol Profile in Wheat

High voltage electrical discharge (HVED) is an eco-friendly low-cost method based on the creation of plasma-activated water (PAW) through the release of electrical discharge in water which results in the formation of reactive particles. Recent studies have reported that such novel plasma technologies promote germination and growth but their hormonal and metabolic background is still not known. In the present work, the HVED-induced hormonal and metabolic changes were studied during the germination of wheat seedlings. Hormonal changes including abscisic acid (ABA), gibberellic acids (GAs), indol acetic acid (IAA) and jasmonic acid (JA) and the polyphenol responses were detected in the early (2nd day) and late (5th day) germination phases of wheat as well as their redistribution in shoot and root. HVED treatment significantly stimulated germination and growth both in the shoot and root. The root early response to HVED involved the upregulation of ABA and increased phaseic and ferulic acid content, while the active form of gibberellic acid (GA1) was downregulated. In the later phase (5th day of germination), HVED had a stimulatory effect on the production of benzoic and salicylic acid. The shoot showed a different response: HVED induced the synthesis of JA_Le_Ile, an active form of JA, and provoked the biosynthesis of cinnamic, p-coumaric and caffeic acid in both phases of germination. Surprisingly, in 2-day-old shoots, HVED decreased the GA20 levels, being intermediate in the synthesis of bioactive gibberellins. These HVED-provoked metabolic changes indicated a stress-related response that could contribute to germination in wheat.

Genome-Wide Characterization and Analysis of the bHLH Transcription Factor Family in Suaeda aralocaspica, an Annual Halophyte With Single-Cell C4 Anatomy

Basic helix-loop-helix (bHLH) transcription factors play important roles in plant growth, development, metabolism, hormone signaling pathways, and responses to abiotic stresses. However, comprehensive genomic and functional analyses of bHLH genes have not yet been reported in desert euhalophytes. Suaeda aralocaspica, an annual C4 halophyte without Kranz anatomy, presents high photosynthetic efficiency in harsh natural habitats and is an ideal plant for identifying transcription factors involved in stress resistance. In this study, 83 bHLH genes in S. aralocaspica were identified and categorized into 21 subfamilies based on conserved motifs, gene structures, and phylogenetic analysis. Functional annotation enrichment revealed that the majority of SabHLHs were enriched in Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways involved in the response to stress conditions, as transcription factors. A number of cis-acting elements related to plant hormones and stress responses were also predicted in the promoter regions of SabHLHs, which were confirmed by expression analysis under various abiotic stress conditions (NaCl, mannitol, low temperature, ABA, GA3, MeJA, and SA); most were involved in tolerance to drought and salinity. SabHLH169 (076) protein localized in the nucleus was involved in transcriptional activity, and gene expression could be affected by different light qualities. This study is the first comprehensive analysis of the bHLH gene family in S. aralocaspica. These data will facilitate further characterization of their molecular functions in the adaptation of desert plants to abiotic stress.

Overexpression of SlPRE5, an atypical bHLH transcription factor, affects plant morphology and chlorophyll accumulation in tomato

The basic helix-loop-helix (bHLH) transcription factors play vital regulatory roles in a series of metabolic, physiological, and developmental processes of plants. Here, SlPRE5, an atypical bHLH gene, was isolated from tomato. SlPRE5 was noticeably expressed in young leaves, sepals, and flowers. SlPRE5-overexpressing plants exhibited rolling leaves with reduced chlorophyll content, increased stem internode length, leaf angle, and compound leaf length. The water loss rate of mature leaves and the content of starch were significantly reduced, while the content of gibberellin was significantly increased in transgenic plants. Yeast two-hybrid and bimolecular fluorescence complementation (BiFC) showed that SlPRE5 could interact with SlAIF1, SlAIF2, and SlPAR1. qRT-PCR and RNA-seq results revealed that the expression levels of genes related to chloroplast development, chlorophyll metabolism, gibberellin metabolism and signal transduction, starch, photosynthesis, and cell expansion were significantly altered in SlPRE5-overexpression plants. Collectively, our results suggest that SlPRE5 is a crucial transcription factor involved in plant morphology and chlorophyll accumulation in tomato leaves.

Regulation of plant immunity and growth by tomato receptor-like cytoplasmic kinase TRK1

The molecular mechanisms of quantitative resistance (QR) to fungal pathogens and their relationships with growth pathways are poorly understood. We identified tomato TRK1 (TPK1b Related Kinase1) and determined its functions in tomato QR and plant growth. TRK1 is a receptor-like cytoplasmic kinase that complexes with tomato LysM Receptor Kinase (SlLYK1). SlLYK1 and TRK1 are required for chitin-induced fungal resistance, accumulation of reactive oxygen species, and expression of immune response genes. Notably, TRK1 and SlLYK1 regulate SlMYC2, a major transcriptional regulator of jasmonic acid (JA) responses and fungal resistance, at transcriptional and post-transcriptional levels. Further, TRK1 is also required for maintenance of proper meristem growth, as revealed by the ectopic meristematic activity, enhanced branching, and altered floral structures in TRK1 RNAi plants. Consistently, TRK1 interacts with SlCLV1 and SlWUS, and TRK1 RNAi plants show increased expression of SlCLV3 and SlWUS in shoot apices. Interestingly, TRK1 suppresses chitin-induced gene expression in meristems but promotes expression of the same genes in leaves. SlCLV1 and TRK1 perform contrasting functions in defense but similar functions in plant growth. Overall, through molecular and biochemical interactions with critical regulators, TRK1 links upstream defense and growth signals to downstream factor in fungal resistance and growth homeostasis response regulators.

Genome-wide survey of the bHLH super gene family in Brassica napus

BACKGROUND

The basic helix-loop-helix (bHLH) gene family is one of the largest transcription factor families in plants and is functionally characterized in diverse species. However, less is known about its functions in the economically important allopolyploid oil crop, Brassica napus.

RESULTS

We identified 602 potential bHLHs in the B. napus genome (BnabHLHs) and categorized them into 35 subfamilies, including seven newly separated subfamilies, based on phylogeny, protein structure, and exon-intron organization analysis. The intron insertion patterns of this gene family were analyzed and a total of eight types were identified in the bHLH regions of BnabHLHs. Chromosome distribution and synteny analyses revealed that hybridization between Brassica rapa and Brassica oleracea was the main expansion mechanism for BnabHLHs. Expression analyses showed that BnabHLHs were widely in different plant tissues and formed seven main patterns, suggesting they may participate in various aspects of B. napus development. Furthermore, when roots were treated with five different hormones (IAA, auxin; GA3, gibberellin; 6-BA, cytokinin; ABA, abscisic acid and ACC, ethylene), the expression profiles of BnabHLHs changed significantly, with many showing increased expression. The induction of five candidate BnabHLHs was confirmed following the five hormone treatments via qRT-PCR. Up to 246 BnabHLHs from nine subfamilies were predicted to have potential roles relating to root development through the joint analysis of their expression profiles and homolog function.

CONCLUSION

The 602 BnabHLHs identified from B. napus were classified into 35 subfamilies, and those members from the same subfamily generally had similar sequence motifs. Overall, we found that BnabHLHs may be widely involved in root development in B. napus. Moreover, this study provides important insights into the potential functions of the BnabHLHs super gene family and thus will be useful in future gene function research.

Jasmonic Acid Signaling Pathway in Response to Abiotic Stresses in Plants

Plants as immovable organisms sense the stressors in their environment and respond to them by means of dedicated stress response pathways. In response to stress, jasmonates (jasmonic acid, its precursors and derivatives), a class of polyunsaturated fatty acid-derived phytohormones, play crucial roles in several biotic and abiotic stresses. As the major immunity hormone, jasmonates participate in numerous signal transduction pathways, including those of gene networks, regulatory proteins, signaling intermediates, and proteins, enzymes, and molecules that act to protect cells from the toxic effects of abiotic stresses. As cellular hubs for integrating informational cues from the environment, jasmonates play significant roles in alleviating salt stress, drought stress, heavy metal toxicity, micronutrient toxicity, freezing stress, ozone stress, CO₂ stress, and light stress. Besides these, jasmonates are involved in several developmental and physiological processes throughout the plant life. In this review, we discuss the biosynthesis and signal transduction pathways of the JAs and the roles of these molecules in the plant responses to abiotic stresses.

Jasmonic Acid Signaling Pathway in Plants

Jasmonic acid (JA) and its precursors and dervatives, referred as jasmonates (JAs) are important molecules in the regulation of many physiological processes in plant growth and development, and especially the mediation of plant responses to biotic and abiotic stresses. JAs biosynthesis, perception, transport, signal transduction and action have been extensively investigated. In this review, we will discuss the initiation of JA signaling with a focus on environmental signal perception and transduction, JA biosynthesis and metabolism, transport of signaling molecules (local transmission, vascular bundle transmission, and airborne transportation), and biological function (JA signal receptors, regulated transcription factors, and biological processes involved).

Genome-wide identification, phylogeny analysis, expression profiling, and determination of protein-protein interactions of the LEUNIG gene family members in tomato

Members of the LEUNIG gene family have recently emerged as key players in gene repression, affecting several developmental mechanisms in plants, especially flower development. LEUNIG proteins function via recruiting adaptor SEUSS proteins. Nevertheless, no systematic studies on the LEUNIG and SEUSS gene families have been undertaken in tomato (Solanum lycopersicum, a fleshy fruit-bearing model plant, belonging to the Solanaceae family). Here, we present the results of a genome-wide analysis of tomato LEUNIG and SEUSS genes. In our study, we identified three SlLUG and four SlSEU genes. All three SlLUG full-length proteins contained the LEUNIG canonical domains (LUFS and two WD40 repeats), and the four full-length SlSEU genes contained the Lim-binding domain. All the members of the SlLUG and SlSEU family proteins were localized to the nucleus. All the SlSEU and SlLUG genes were detected in the tomato tissues tested. Expression analysis showed that the SlLUGs and SlSEUs exhibited tissue-specific expression, and that they responded to exogenous plant hormone and stress treatment. Protein-protein interaction analysis showed that only SlLUGs, but not SlSEUs, interacted with SlYABBY. Only a weak interaction between SlLUG1 and SlSEU3 was observed among all the SlLUG and SlSEU proteins. Taken together, these findings may help elucidate the roles played by SlLUG and SlSEU family members in plant growth and development.

Jasmonate signalling pathway in strawberry: Genome-wide identification, molecular characterization and expression of JAZs and MYCs during fruit development and ripening

Jasmonates (JAs) are signalling molecules involved in stress responses, development and secondary metabolism biosynthesis, although their roles in fleshy-fruit development and ripening processes are not well known. In strawberry fruit, it has been proposed that JAs could regulate the early development through the activation of the JAs biosynthesis. Moreover, it has been reported that JA treatment increases anthocyanin content in strawberry fruit involving the bioactive jasmonate biosynthesis. Nevertheless, JA signalling pathway, of which main components are the COI1-JAZ co-receptor and the MYC transcription factors (TFs), has not been characterized in strawberry until now. Here we identified and characterized the woodland strawberry (Fragaria vesca) JAZ and MYC genes as well as studied their expression during development and ripening stages in commercial strawberry (Fragaria × ananassa) fruit. We described twelve putative JAZ proteins and two MYC TFs, which showed high conservation with respect to their orthologs in Arabidopsis thaliana and in other fleshy-fruit species such as Malus × domestica, Vitis vinifera and Solanum lycopersicum as revealed by gene synteny and phylogenetic analyses. Noteworthy, their expression levels exhibited a significant decrease from fruit development to ripening stages in F. × ananassa, along with others of the JA signalling-related genes such as FaNINJA and FaJAMs, encoding for negative regulators of JA responses. Moreover, we found that main JA signalling-related genes such as FaMYC2, and FaJAZ1 are promptly induced by JA treatment at early times in F. × ananassa fruit. These results suggest the conservation of the canonical JA signalling pathway in strawberry and a possible role of this pathway in early strawberry fruit development, which also correlates negatively with the beginning of the ripening process.

FIN219/JAR1 and cryptochrome1 antagonize each other to modulate photomorphogenesis under blue light in Arabidopsis

Plant development is affected by the integration of light and phytohormones, including jasmonates (JAs). To address the molecular mechanisms of possible interactions between blue light and JA signaling in Arabidopsis thaliana, we used molecular and transgenic approaches to understand the regulatory relationships between FAR-RED INSENSITIVE 219 (FIN219)/JASMONATE RESISTANT1 (JAR1) and the blue-light photoreceptor cryptochrome1 (CRY1). FIN219 overexpression in the wild type resulted in a short-hypocotyl phenotype under blue light. However, FIN219 overexpression in cry1, cry2 and cry1cry2 double mutant backgrounds resulted in phenotypes similar to their respective mutant backgrounds, which suggests that FIN219 function may require blue light photoreceptors. Intriguingly, FIN219 overexpression in transgenic plants harboring ectopic expression of the C terminus of CRY1 (GUS-CCT1), which exhibits a hypersensitive short-hypocotyl phenotype in all light conditions including darkness, led to a rescued phenotype under all light conditions except red light. Further expression studies showed mutual suppression between FIN219 and CRY1 under blue light. Strikingly, FIN219 overexpression in GUS-CCT1 transgenic lines (FIN219-OE/GUS-CCT1) abolished GUS-CCT1 fusion protein under blue light, whereas GUS-CCT1 fusion protein was stable in the fin219-2 mutant background (fin219-2/GUS-CCT1). Moreover, FIN219 strongly interacted with COP1 under blue light, and methyl JA (MeJA) treatment enhanced the interaction between FIN219 and GUS-CCT1 under blue light. Furthermore, FIN219 level affected GUS-CCT1 seedling responses such as anthocyanin accumulation and bacterial resistance under various light conditions and MeJA treatment. Thus, FIN219/JAR1 and CRY1 antagonize each other to modulate photomorphogenic development of seedlings and stress responses in Arabidopsis.

Dissecting molecular and physiological response mechanisms to high solar radiation in cyanic and acyanic leaves: a case study on red and green basil

Photosynthetic performance and the expression of genes involved in light signaling and the biosynthesis of isoprenoids and phenylpropanoids were analysed in green ('Tigullio', TIG) and red ('Red Rubin', RR) basil. The aim was to detect the physiological and molecular response mechanisms to high sunlight. The attenuation of blue-green light by epidermal anthocyanins was shown to evoke shade-avoidance responses with consequential effects on leaf morpho-anatomical traits and gas exchange performance. Red basil had a lower mesophyll conductance, partially compensated by the less effective control of stomatal movements, in comparison with TIG. Photosynthesis decreased more in TIG than in RR in high sunlight, because of larger stomatal limitations and the transient impairment of PSII photochemistry. The methylerythritol 4-phosphate pathway promoted above all the synthesis and de-epoxidation of violaxanthin-cycle pigments in TIG and of neoxanthin and lutein in RR. This enabled the green leaves to process the excess radiant energy effectively, and the red leaves to optimize light harvesting and photoprotection. The greater stomatal closure observed in TIG than in RR was due to enhanced abscisic acid (ABA) glucose ester deglucosylation and reduced ABA oxidation, rather than to superior de novo ABA synthesis. This study shows a strong competition between anthocyanin and flavonol biosynthesis, which occurs at the level of genes regulating the oxidation of the C2-C3 bond in the dihydro-flavonoid skeleton.

Tomato histone H2B monoubiquitination enzymes SlHUB1 and SlHUB2 contribute to disease resistance against Botrytis cinerea through modulating the balance between SA- and JA/ET-mediated signaling pathways

BACKGROUND

Histone H2B monoubiquitination pathway has been shown to play critical roles in regulating growth/development and stress response in Arabidopsis. In the present study, we explored the involvement of the tomato histone H2B monoubiquitination pathway in defense response against Botrytis cinerea by functional analysis of SlHUB1 and SlHUB2, orthologues of the Arabidopsis AtHUB1/AtHUB2.

METHODS

We used the TRV-based gene silencing system to knockdown the expression levels of SlHUB1 or SlHUB2 in tomato plants and compared the phenotype between the silenced and the control plants after infection with B. cinerea and Pseudomonas syringae pv. tomato (Pst) DC3000. Biochemical and interaction properties of proteins were examined using in vitro histone monoubiquitination and yeast two-hybrid assays, respectively. The transcript levels of genes were analyzed by quantitative real time PCR (qRT-PCR).

RESULTS

The tomato SlHUB1 and SlHUB2 had H2B monoubiquitination E3 ligases activity in vitro and expression of SlHUB1 and SlHUB2 was induced by infection of B. cinerea and Pst DC3000 and by treatment with salicylic acid (SA) and 1-amino cyclopropane-1-carboxylic acid (ACC). Silencing of either SlHUB1 or SlHUB2 in tomato plants showed increased susceptibility to B. cinerea, whereas silencing of SlHUB1 resulted in increased resistance against Pst DC3000. SlMED21, a Mediator complex subunit, interacted with SlHUB1 but silencing of SlMED21 did not affect the disease resistance to B. cinerea and Pst DC3000. The SlHUB1- and SlHUB2-silenced plants had thinner cell wall but increased accumulation of reactive oxygen species (ROS), increased callose deposition and exhibited altered expression of the genes involved in phenylpropanoid pathway and in ROS generation and scavenging system. Expression of genes in the SA-mediated signaling pathway was significantly upregulated, whereas expression of genes in the jasmonic acid (JA)/ethylene (ET)-mediated signaling pathway were markedly decreased in SlHUB1- and SlHUB2-silenced plants after infection of B. cinerea.

CONCLUSION

VIGS-based functional analyses demonstrate that both SlHUB1 and SlHUB2 contribute to resistance against B. cinerea most likely through modulating the balance between the SA- and JA/ET-mediated signaling pathways.

On reproduction in red algae: further research needed at the molecular level

Multicellular red algae (Rhodophyta) have some of the most complex life cycles known in living organisms. Economically valuable seaweeds, such as phycocolloid producers, have a triphasic (gametophyte, carposporophyte, and tetrasporophyte) life cycle, not to mention the intricate alternation of generations in the edible "sushi-alga" nori. It is a well-known fact that reproductive processes are controlled by one or more abiotic factor(s), including day length, light quality, temperature, and nutrients. Likewise, endogenous chemical factors such as plant growth regulators have been reported to affect reproductive events in some red seaweeds. Still, in the genomic era and given the high throughput techniques at our disposal, our knowledge about the endogenous molecular machinery lags far behind that of higher plants. Any potential effective control of the reproductive process will entail revisiting most of these results and facts to answer basic biological questions as yet unresolved. Recent results have shed light on the involvement of several genes in red alga reproductive events. In addition, a working species characterized by a simple filamentous architecture, easy cultivation, and accessible genomes may also facilitate our task.