Phytosulfokine peptide optimizes plant growth and defense via glutamine synthetase GS2 phosphorylation in tomato.

Phytosulfokine (PSK) is a plant pentapeptide hormone that fulfills a wide range of functions. Although PSK has frequently been reported to function in the inverse regulation of growth and defense in response to (hemi)biotrophic pathogens, the mechanisms involved remain largely unknown. Using the tomato (Solanum lycopersicum) and Pseudomonas syringae pv. tomato (Pst) DC3000 pathogen system, we present compelling evidence that the PSK receptor PSKR1 interacts with the calcium-dependent protein kinase CPK28, which in turn phosphorylates the key enzyme of nitrogen assimilation glutamine synthetase GS2 at two sites (Serine-334 and Serine-360). GS2 phosphorylation at S334 specifically regulates plant defense, whereas S360 regulates growth, uncoupling the PSK-induced effects on defense responses and growth regulation. The discovery of these sites will inform breeding strategies designed to optimize the growth-defense balance in a compatible manner.

An atlas of the tomato epigenome reveals that KRYPTONITE shapes TAD-like boundaries through the control of H3K9ac distribution.

In recent years, the exploration of genome three-dimensional (3D) conformation has yielded profound insights into the regulation of gene expression and cellular functions in both animals and plants. While animals exhibit a characteristic genome topology defined by topologically associating domains (TADs), plants display similar features with a more diverse conformation across species. Employing advanced high-throughput sequencing and microscopy techniques, we investigated the landscape of 26 histone modifications and RNA polymerase II distribution in tomato (Solanum lycopersicum). Our study unveiled a rich and nuanced epigenetic landscape, shedding light on distinct chromatin states associated with heterochromatin formation and gene silencing. Moreover, we elucidated the intricate interplay between these chromatin states and the overall topology of the genome. Employing a genetic approach, we delved into the role of the histone modification H3K9ac in genome topology. Notably, our investigation revealed that the ectopic deposition of this chromatin mark triggered a reorganization of the 3D chromatin structure, defining different TAD-like borders. Our work emphasizes the critical role of H3K9ac in shaping the topology of the tomato genome, providing valuable insights into the epigenetic landscape of this agriculturally significant crop species.

Rhizogenic Agrobacterium protein RolB interacts with the TOPLESS repressor proteins to reprogram plant immunity and development.

Rhizogenic Agrobacterium strains comprise biotrophic pathogens that cause hairy root disease (HRD) on hydroponically grown Solanaceae and Cucurbitaceae crops, besides being widely explored agents for the creation of hairy root cultures for the sustainable production of plant-specialized metabolites. Hairy root formation is mediated through the expression of genes encoded on the T-DNA of the root-inducing (Ri) plasmid, of which several, including root oncogenic locus B (rolB), play a major role in hairy root development. Despite decades of research, the exact molecular function of the proteins encoded by the rol genes remains enigmatic. Here, by means of TurboID-mediated proximity labeling in tomato (Solanum lycopersicum) hairy roots, we identified the repressor proteins TOPLESS (TPL) and Novel Interactor of JAZ (NINJA) as direct interactors of RolB. Although these interactions allow RolB to act as a transcriptional repressor, our data hint at another in planta function of the RolB oncoprotein. Hence, by a series of plant bioassays, transcriptomic and DNA-binding site enrichment analyses, we conclude that RolB can mitigate the TPL functioning so that it leads to a specific and partial reprogramming of phytohormone signaling, immunity, growth, and developmental processes. Our data support a model in which RolB manipulates host transcription, at least in part, through interaction with TPL, to facilitate hairy root development. Thereby, we provide important mechanistic insights into this renowned oncoprotein in HRD.

SlBTB19 interacts with SlWRKY2 to suppress cold tolerance in tomato via the CBF pathway.

Cold stress restricts the metabolic and physiological activities of plants, thereby affecting their growth and development. Although broad-complex, tramtrack, and bric-à-brac (BTB) proteins are essential for diverse biological processes and stress responses, the mechanisms underlying BTB-mediated cold responses remain not fully understood. Here, we characterize the function of the cold-induced SlBTB19 protein in tomato (Solanum lycopersicum). Overexpression of SlBTB19 resulted in increased plant sensitivity to cold stress, whereas SlBTB19 knockout mutants exhibited a cold-tolerance phenotype. Further analyses, including protein-protein interaction studies and cell-free degradation assays, revealed that SlBTB19 interacts with and destabilizes the transcription factor SlWRKY2. Using virus-induced gene silencing (VIGS) to silence SlWRKY2 in both wild-type and slbtb19 mutants, we provided genetic evidence that SlWRKY2 acts downstream of SlBTB19 in regulating cold tolerance. Importantly, we demonstrated that SlWRKY2 positively regulates cold tolerance in a CRT/DRE binding factor (CBF)-dependent manner. Under cold stress, SlWRKY2 binds to the W-box in the CBF1 and CBF3 promoters, directly activating their expression. In summary, our findings identify a SlBTB19-SlWRKY2 module that negatively regulates the CBF-dependent cold tolerance pathway in tomato.

The tomato P69 subtilase family is involved in resistance to bacterial wilt.

The intercellular space or apoplast constitutes the main interface in plant-pathogen interactions. Apoplastic subtilisin-like proteases-subtilases-may play an important role in defence and they have been identified as targets of pathogen-secreted effector proteins. Here, we characterise the role of the Solanaceae-specific P69 subtilase family in the interaction between tomato and the vascular bacterial wilt pathogen Ralstonia solanacearum. R. solanacearum infection post-translationally activated several tomato P69s. Among them, P69D was exclusively activated in tomato plants resistant to R. solanacearum. In vitro experiments showed that P69D activation by prodomain removal occurred in an autocatalytic and intramolecular reaction that does not rely on the residue upstream of the processing site. Importantly P69D-deficient tomato plants were more susceptible to bacterial wilt and transient expression of P69B, D and G in Nicotiana benthamiana limited proliferation of R. solanacearum. Our study demonstrates that P69s have conserved features but diverse functions in tomato and that P69D is involved in resistance to R. solanacearum but not to other vascular pathogens like Fusarium oxysporum.

Helper NLRs Nrc2 and Nrc3 act codependently with Prf/Pto and activate MAPK signaling to induce immunity in tomato.

Plant intracellular immune receptors, primarily nucleotide-binding, leucine-rich repeat proteins (NLRs), detect pathogen effector proteins and activate NLR-triggered immunity (NTI). Recently, 'sensor' NLRs have been reported to function with 'helper' NLRs to activate immunity. We investigated the role of two helper NLRs, Nrc2 and Nrc3, on immunity in tomato to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) mediated by the sensor NLR Prf and the Pto kinase. An nrc2/nrc3 mutant no longer activated Prf/Pto-mediated NTI to Pst containing the effectors AvrPto and AvrPtoB. An nrc3 mutant showed intermediate susceptibility between wild-type plants and a Prf mutant, while an nrc2 mutant developed only mild disease. These observations indicate that Nrc2 and Nrc3 act additively in Prf-/Pto-mediated immunity. We examined at what point Nrc2 and Nrc3 act in the Prf/Pto-mediated immune response. In the nrc2/3 mutant, programmed cell death (PCD) normally induced by constitutively active variants of AvrPtoB, Pto, or Prf was abolished, but that induced by M3Kα or Mkk2 was not. PCD induced by a constitutively active Nrc3 was also abolished in a Nicotiana benthamiana line with reduced expression of Prf. MAPK activation triggered by expression of AvrPto in the wild-type tomato plants was completely abolished in the nrc2/3 mutant. These results indicate that Nrc2 and Nrc3 act with Prf/Pto and upstream of MAPK signaling. Nrc2 and Nrc3 were not required for PCD triggered by Ptr1, another sensor NLR-mediating Pst resistance, although these helper NLRs do appear to be involved in resistance to certain Pst race 1 strains.

PP2C phosphatase Pic14 negatively regulates tomato Pto/Prf-triggered immunity by inhibiting MAPK activation.

Type 2C protein phosphatases (PP2Cs) are emerging as important regulators of plant immune responses, although little is known about how they might impact nucleotide-binding, leucine-rich repeat (NLR)-triggered immunity (NTI). We discovered that expression of the PP2C immunity-associated candidate 14 gene (Pic14) is induced upon activation of the Pto/Prf-mediated NTI response in tomato. Pto/Prf recognizes the effector AvrPto translocated into plant cells by the pathogen Pseudomonas syringae pv. tomato (Pst) and activate a MAPK cascade and other responses which together confer resistance to bacterial speck disease. Pic14 encodes a PP2C with an N-terminal kinase-interacting motif (KIM) and a C-terminal phosphatase domain. Upon inoculation with Pst-AvrPto, Pto/Prf-expressing tomato plants with loss-of-function mutations in Pic14 developed less speck disease, specifically in older leaves, compared to wild-type plants. Transient expression of Pic14 in leaves of Nicotiana benthamiana and tomato inhibited cell death typically induced by Pto/Prf and the MAPK cascade members M3Kα and Mkk2. The cell death-suppressing activity of Pic14 was dependent on the KIM and the catalytic phosphatase domain. Pic14 inhibited M3Kα- and Mkk2-mediated activation of immunity-associated MAPKs and Pic14 was shown to be an active phosphatase that physically interacts with and dephosphorylates Mkk2 in a KIM-dependent manner. Together, our results reveal Pic14 as an important negative regulator of Pto/Prf-triggered immunity by interacting with and dephosphorylating Mkk2.

The apocarotenoid ß-ionone regulates the transcriptome of Arabidopsis thaliana and increases its resistance against Botrytis cinerea.

Carotenoids are isoprenoid pigments indispensable for photosynthesis. Moreover, they are the precursor of apocarotenoids, which include the phytohormones abscisic acid (ABA) and strigolactones (SLs) as well as retrograde signaling molecules and growth regulators, such as ß-cyclocitral and zaxinone. Here, we show that the application of the volatile apocarotenoid ß-ionone (ß-I) to Arabidopsis plants at micromolar concentrations caused a global reprogramming of gene expression, affecting thousands of transcripts involved in stress tolerance, growth, hormone metabolism, pathogen defense, and photosynthesis. This transcriptional reprogramming changes, along with induced changes in the level of the phytohormones ABA, jasmonic acid, and salicylic acid, led to enhanced Arabidopsis resistance to the widespread necrotrophic fungus Botrytis cinerea (B.c.) that causes the gray mold disease in many crop species and spoilage of harvested fruits. Pre-treatment of tobacco and tomato plants with ß-I followed by inoculation with B.c. confirmed the effect of ß-I in increasing the resistance to this pathogen in crop plants. Moreover, we observed reduced susceptibility to B.c. in fruits of transgenic tomato plants overexpressing LYCOPENE ß-CYCLASE, which contains elevated levels of endogenous ß-I, providing a further evidence for its effect on B.c. infestation. Our work unraveled ß-I as a further carotenoid-derived regulatory metabolite and indicates the possibility of establishing this natural volatile as an environmentally friendly bio-fungicide to control B.c.

RNA-protein interactions reveals the pivotal role of lncRNA1840 in tomato fruit maturation.

Long non-coding RNAs (lncRNAs) play crucial roles in various biological processes in plants. However, the functional mechanism of lncRNAs in fruit ripening, particularly the transition from unripe to ripe stages, remains elusive. One such lncRNA1840, reported by our group, was found to have important role in tomato fruit ripening. In the present study, we gain insight into its functional role in fruit ripening. CRISPR-Cas9 mediated lncRNA1840 mutants caused the delayed tomato fruit ripening. Notably, loss function of lncRNA1840 did not directly impact ethylene signaling but rather delay ethylene synthesis. Transcriptomic analysis revealed differences in the expression of ripening related genes in lncRNA1840 mutants, suggesting that it is involved in gene regulation of fruit ripening. We used Chromatin Isolation by RNA Purification (ChIRP)-Seq to identify lncRNA1840 binding sites on chromatin. ChIRP-seq suggested that lncRNA1840 had occupancy on 40 genes, but none of them is differentially expressed genes in transcriptomic analysis, which indicated lncRNA1840 might indirectly modulate the gene expression. ChIRP-mass spectrometry analysis identified potential protein interactors of lncRNA1840, Pre-mRNA processing splicing factor 8, highlighting its involvement in post-transcriptional regulatory pathways. In summary, lncRNA1840 is key player in tomato plant growth and fruit ripening, with multifaceted roles in gene expression and regulatory networks.

Class II knotted-like homeodomain protein SlKN5 with BEL1-like homeodomain proteins suppresses fruit greening in tomato fruit.

Knotted1-like homeodomain (KNOX) proteins are essential in regulating plant organ differentiation. Land plants, including tomato (Solanum lycopersicum), have two classes of the KNOX protein family, namely, class I (KNOX I) and class II KNOX (KNOX II). While tomato KNOX I proteins are known to stimulate chloroplast development in fruit, affecting fruit coloration, the role of KNOX II proteins in this context remains unclear. In this study, we employ CRISPR/Cas9 to generate knockout mutants of the KNOX II member, SlKN5. These mutants display increased leaf complexity, a phenotype commonly associated with reduced KNOX II activity, as well as enhanced accumulation of chloroplasts and chlorophylls in smaller cells within young, unripe fruit. RNA-seq data analyses indicate that SlKN5 suppresses the transcriptions of genes involved in chloroplast biogenesis, chlorophyll biosynthesis, and gibberellin catabolism. Furthermore, protein-protein interaction assays reveal that SlKN5 physically interacts with three transcriptional repressors from the BLH1-clade of BEL1-like homeodomain (BLH) protein family, SlBLH4, SlBLH5, and SlBLH7, with SlBLH7 showing the strongest interaction. CRISPR/Cas9-mediated knockout of these SlBLH genes confirmed their overlapping roles in suppressing chloroplast biogenesis, chlorophyll biosynthesis, and lycopene cyclization. Transient assays further demonstrate that the SlKN5-SlBLH7 interaction enhances binding capacity to regulatory regions of key chloroplast- and chlorophyll-related genes, including SlAPRR2-like1, SlCAB-1C, and SlGUN4. Collectively, our findings elucidate that the KNOX II SlKN5-SlBLH regulatory modules serve to inhibit fruit greening and subsequently promote lycopene accumulation, thereby fine-tuning the color transition from immature green fruit to mature red fruit.

A Solanum lycopersicum polyamine oxidase contributes to the control of plant growth, xylem differentiation, and drought stress tolerance.

Polyamines are involved in several plant physiological processes. In Arabidopsis thaliana, five FAD-dependent polyamine oxidases (AtPAO1 to AtPAO5) contribute to polyamine homeostasis. AtPAO5 catalyzes the back-conversion of thermospermine (T-Spm) to spermidine and plays a role in plant development, xylem differentiation, and abiotic stress tolerance. In the present study, to verify whether T-Spm metabolism can be exploited as a new route to improve stress tolerance in crops and to investigate the underlying mechanisms, tomato (Solanum lycopersicum) AtPAO5 homologs were identified (SlPAO2, SlPAO3, and SlPAO4) and CRISPR/Cas9-mediated loss-of-function slpao3 mutants were obtained. Morphological, molecular, and physiological analyses showed that slpao3 mutants display increased T-Spm levels and exhibit changes in growth parameters, number and size of xylem elements, and expression levels of auxin- and gibberellin-related genes compared to wild-type plants. The slpao3 mutants are also characterized by improved tolerance to drought stress, which can be attributed to a diminished xylem hydraulic conductivity that limits water loss, as well as to a reduced vulnerability to embolism. Altogether, this study evidences conservation, though with some significant variations, of the T-Spm-mediated regulatory mechanisms controlling plant growth and differentiation across different plant species and highlights the T-Spm role in improving stress tolerance while not constraining growth.

Related type 2C protein phosphatases Pic3 and Pic12 negatively regulate immunity in tomato to Pseudomonas syringae.

Type 2C protein phosphatases (PP2Cs) constitute a large family in most plant species but relatively few of them have been implicated in immunity. To identify and characterize PP2C phosphatases that affect tomato (Solanum lycopersicum) immunity, we used CRISPR/Cas9 to generate loss-of-function mutations in 11 PP2C-encoding genes whose expression is altered in response to immune elicitors or pathogens. We report that two closely related PP2C phosphatases, Pic3 (PP2C immunity-associated candidate 3) and Pic12, are involved in regulating resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Loss-of-function mutations in Pic3 led to enhanced resistance to Pst in older but not younger leaves, whereas such mutations in Pic12 resulted in enhanced resistance in both older and younger leaves. Overexpression of Pic3 and Pic12 proteins in leaves of Nicotiana benthamiana inhibited resistance to Pst, and this effect was dependent on Pic3/12 phosphatase activity and an N-terminal palmitoylation motif associated with localization to the cell periphery. Pic3, but not Pic12, had a slight negative effect on flagellin-associated reactive oxygen species generation, although their involvement in the response to Pst appeared independent of flagellin. RNA-sequencing analysis of Rio Grande (RG)-PtoR wild-type plants and two independent RG-pic3 mutants revealed that the enhanced disease resistance in RG-pic3 older leaves is associated with increased transcript abundance of multiple defense related genes. RG-pic3/RG-pic12 double mutant plants exhibited stronger disease resistance than RG-pic3 or RG-pic12 single mutants. Together, our results reveal that Pic3 and Pic12 negatively regulate tomato immunity in an additive manner through flagellin-independent pathways.

The MADS-box protein SlTAGL1 regulates a ripening-associated SlDQD/SDH2 involved in flavonoid biosynthesis and resistance against Botrytis cinerea in post-harvest tomato fruit.

3-Dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH) is a key rate-limiting enzyme that catalyzes the synthesis of the shikimate, which is an important metabolic intermediate in plants and animals. However, the function of SlDQD/SDH family genes in tomato (Solanum lycopersicum) fruit metabolites is still unknown. In the present study, we identified a ripening-associated SlDQD/SDH member, SlDQD/SDH2, that plays a key role in shikimate and flavonoid metabolism. Overexpression of this gene resulted in an increased content of shikimate and flavonoids, while knockout of this gene by CRISPR/Cas9 mediated gene editing led to a significantly lower content of shikimate and flavonoids by downregulation of flavonoid biosynthesis-related genes. Moreover, we showed that SlDQD/SDH2 confers resistance against Botrytis cinerea attack in post-harvest tomato fruit. Dual-luciferase reporter and EMSA assays indicated that SlDQD/SDH2 is a direct target of the key ripening regulator SlTAGL1. In general, this study provided a new insight into the biosynthesis of flavonoid and B. cinerea resistance in fruit tomatoes.

Diurnal gene oscillations modulated by RNA metabolism in tomato.

Diurnal rhythms are known to regulate the expression of a large number of genes, coordinating plant growth and development with diel changes in light and temperature. However, the impact of RNA metabolism on rhythmic gene oscillations in plant is not yet fully understood. To address this question, we performed transcriptome and degradome profiling on tomato leaves at 6 time points during one 24 h cycle, using RNA-seq and genome-wide mapping of uncapped and cleavage transcripts (GMUCT). Time-series profiling of RNA-seq revealed 9342 diurnal-oscillated genes, which were enriched in various metabolic processes. To quantify the general level of RNA degradation for each gene, we utilized the Proportion Uncapped (PU) metric, which represents the GMUCT/RNA-seq ratio. Oscillated PU analysis revealed that 3885 genes were regulated by rhythmic RNA degradation. The RNA decay of these diurnal genes was highly coordinated with mRNA downregulation during oscillation, highlighting the critical role of internal transcription-degradation balance in rhythmic gene oscillation. Furthermore, we identified 2190 genes undergoing co-translational RNA decay (CTRD) with 5' phosphate read ends enriched at the boundary of ribosomes stalling at translational termination sites. Interestingly, diurnal-changed mRNAs with large amplitudes tended to be co-translationally decay, suggesting that CTRD contributed to the rapid turnover of diurnal mRNAs. Finally, we also identified several genes, whose miRNA cleavage efficiency oscillated in a diurnal manner. Taken together, these findings uncovered the vital functions of RNA metabolism, including rhythmic RNA degradation, CTRD, and miRNA cleavage, in modulating the diurnal mRNA oscillations during diel change at post-transcriptional level in tomato.

Image-based assessment of plant disease progression identifies new genetic loci for resistance to Ralstonia solanacearum in tomato.

A major challenge in global crop production is mitigating yield loss due to plant diseases. One of the best strategies to control these losses is through breeding for disease resistance. One barrier to the identification of resistance genes is the quantification of disease severity, which is typically based on the determination of a subjective score by a human observer. We hypothesized that image-based, non-destructive measurements of plant morphology over an extended period after pathogen infection would capture subtle quantitative differences between genotypes, and thus enable identification of new disease resistance loci. To test this, we inoculated a genetically diverse biparental mapping population of tomato (Solanum lycopersicum) with Ralstonia solanacearum, a soilborne pathogen that causes bacterial wilt disease. We acquired over 40 000 time-series images of disease progression in this population, and developed an image analysis pipeline providing a suite of 10 traits to quantify bacterial wilt disease based on plant shape and size. Quantitative trait locus (QTL) analyses using image-based phenotyping for single and multi-traits identified QTLs that were both unique and shared compared with those identified by human assessment of wilting, and could detect QTLs earlier than human assessment. Expanding the phenotypic space of disease with image-based, non-destructive phenotyping both allowed earlier detection and identified new genetic components of resistance.

The bZIP transcription factor SlAREB1 regulates anthocyanin biosynthesis in response to low temperature in tomato.

Low temperature and abscisic acid (ABA) are the two main factors that induce anthocyanin synthesis; however, their potential relationships in governing anthocyanin biosynthesis in Solanum lycopersicum (tomato) seedlings remains unclear. Our study revealed the involvement of the transcription factor SlAREB1 in the low-temperature response of tomato seedlings via the ABA-dependent pathway, for a specific temperature range. The overexpression of SlAREB1 enhanced the expression of anthocyanin-related genes and the accumulation of anthocyanins, especially under low-temperature conditions, whereas silencing SlAREB1 dramatically reduced gene expression and anthocyanin accumulation. There is a direct interaction between SlAREB1 and the promoters of SlDFR and SlF3'5'H, which are structural genes that impact anthocyanin biosynthesis. SlAREB1 can regulate anthocyanins through controlling SlDFR and SlF3'5'H expression. Accordingly, SlAREB1 takes charge of regulating anthocyanin biosynthesis in tomato seedlings via the ABA-dependent pathway at low temperatures.

Deregulation of ζ-carotene desaturase in Arabidopsis and tomato exposes a unique carotenoid-derived redundant regulation of floral meristem identity and function.

A level of redundancy and interplay among the transcriptional regulators of floral development safeguards a plant's reproductive success and ensures crop production. In the present study, an additional layer of complexity in the regulation of floral meristem (FM) identity and flower development is elucidated linking carotenoid biosynthesis and metabolism to the regulation of determinate flowering. The accumulation and subsequent cleavage of a diverse array of ζ-carotenes in the chloroplast biogenesis 5 (clb5) mutant of Arabidopsis results in the reprogramming of meristematic gene regulatory networks establishing FM identity mirroring that of the FM identity master regulator, APETALA1 (AP1). The immediate transition to floral development in clb5 requires long photoperiods in a GIGANTEA-independent manner, whereas AP1 is essential for the floral organ development of clb5. The elucidation of this link between carotenoid metabolism and floral development translates to tomato exposing a regulation of FM identity redundant to and initiated by AP1 and proposed to be dependent on the E class floral initiation and organ identity regulator, SEPALLATA3 (SEP3).

Exploring the gene expression network involved in the heat stress response of a thermotolerant tomato genotype.

BACKGROUND: The increase in temperatures due to the current climate change dramatically affects crop cultivation, resulting in yield losses and altered fruit quality. Tomato is one of the most extensively grown and consumed horticultural products, and although it can withstand a wide range of climatic conditions, heat stress can affect plant growth and development specially on the reproductive stage, severely influencing the final yield. In the present work, the heat stress response mechanisms of one thermotolerant genotype (E42) were investigated by exploring its regulatory gene network. This was achieved through a promoter analysis based on the identification of the heat stress elements (HSEs) mapping in the promoters, combined with a gene co-expression network analysis aimed at identifying interactions among heat-related genes. RESULTS: Results highlighted 82 genes presenting HSEs in the promoter and belonging to one of the 52 gene networks obtained by the GCN analysis; 61 of these also interact with heat shock factors (Hsfs). Finally, a list of 13 candidate genes including two Hsfs, nine heat shock proteins (Hsps) and two GDSL esterase/lipase (GELPs) were retrieved by focusing on those E42 genes exhibiting HSEs in the promoters, interacting with Hsfs and showing variants, compared to Heinz reference genome, with HIGH and/or MODERATE impact on the translated protein. Among these, the Gene Ontology annotation analysis evidenced that only LeHsp100 (Solyc02g088610) belongs to a network specifically involved in the response to heat stress. CONCLUSIONS: As a whole, the combination of bioinformatic analyses carried out on genomic and trascriptomic data available for tomato, together with polymorphisms detected in HS-related genes of the thermotolerant E42 allowed to determine a subset of candidate genes involved in the HS response in tomato. This study provides a novel approach in the investigation of abiotic stress response mechanisms and further studies will be conducted to validate the role of the highlighted genes.

Identification of tomato F-box proteins functioning in phenylpropanoid metabolism.

Phenylpropanoids, a class of specialized metabolites, play crucial roles in plant growth and stress adaptation and include diverse phenolic compounds such as flavonoids. Phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) are essential enzymes functioning at the entry points of general phenylpropanoid biosynthesis and flavonoid biosynthesis, respectively. In Arabidopsis, PAL and CHS are turned over through ubiquitination-dependent proteasomal degradation. Specific kelch domain-containing F-Box (KFB) proteins as components of ubiquitin E3 ligase directly interact with PAL or CHS, leading to polyubiquitinated PAL and CHS, which in turn influences phenylpropanoid and flavonoid production. Although phenylpropanoids are vital for tomato nutritional value and stress responses, the post-translational regulation of PAL and CHS in tomato remains unknown. We identified 31 putative KFB-encoding genes in the tomato genome. Our homology analysis and phylogenetic study predicted four PAL-interacting SlKFBs, while SlKFB18 was identified as the sole candidate for the CHS-interacting KFB. Consistent with their homolog function, the predicted four PAL-interacting SlKFBs function in PAL degradation. Surprisingly, SlKFB18 did not interact with tomato CHS and the overexpression or knocking out of SlKFB18 did not affect phenylpropanoid contents in tomato transgenic lines, suggesting its irreverence with flavonoid metabolism. Our study successfully discovered the post-translational regulatory machinery of PALs in tomato while highlighting the limitation of relying solely on a homology-based approach to predict interacting partners of F-box proteins.

Bacteria from the skin of amphibians promote growth of Arabidopsis thaliana and Solanum lycopersicum by modifying hormone-related transcriptome response.

Plants and microorganisms establish beneficial associations that can improve their development and growth. Recently, it has been demonstrated that bacteria isolated from the skin of amphibians can contribute to plant growth and defense. However, the molecular mechanisms involved in the beneficial effect for the host are still unclear. In this work, we explored whether bacteria isolated from three tropical frogs species can contribute to plant growth. After a wide screening, we identified three bacterial strains with high biostimulant potential, capable of modifying the root structure of Arabidopsis thaliana plants. In addition, applying individual bacterial cultures to Solanum lycopersicum plants induced an increase in their growth. To understand the effect that these microorganisms have over the host plant, we analysed the transcriptomic profile of A. thaliana during the interaction with the C32I bacterium, demonstrating that the presence of the bacteria elicits a transcriptional response associated to plant hormone biosynthesis. Our results show that amphibian skin bacteria can function as biostimulants to improve agricultural crops growth and development by modifying the plant transcriptomic responses.