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Plant disease limits crop production, and host genetic resistance is a major means of control. Plant pathogenic Ralstonia causes bacterial wilt disease and is best controlled with resistant varieties. Tomato wilt resistance is multigenic, yet the mechanisms of resistance remain largely unknown. We combined metaRNAseq analysis and functional experiments to identify core Ralstonia‐responsive genes and the corresponding biological mechanisms in wilt‐resistant and wilt‐susceptible tomatoes. While trade‐offs between growth and defence are common in plants, wilt‐resistant plants activated both defence responses and growth processes. Measurements of innate immunity and growth, including reactive oxygen species production and root system growth, respectively, validated that resistant plants executed defence‐related processes at the same time they increased root growth. In contrast, in wilt‐susceptible plants roots senesced and root surface area declined following Ralstonia inoculation. Wilt‐resistant plants repressed genes predicted to negatively regulate water stress tolerance, while susceptible plants repressed genes predicted to promote water stress tolerance. Our results suggest that wilt‐resistant plants can simultaneously promote growth and defence by investing in resources that act in both processes. Infected susceptible plants activate defences, but fail to grow and so succumb to Ralstonia, likely because they cannot tolerate the water stress induced by vascular wilt. [ABSTRACT FROM AUTHOR]

Hypocotyl elongation is dramatically influenced by environmental factors and phytohormones. Indole‐3‐acetic acid (IAA) plays a prominent role in hypocotyl elongation, whereas abscisic acid (ABA) is regarded as an inhibitor through repressing IAA synthesis and signalling. However, the regulatory role of ABA in local IAA deactivation remains largely uncharacterized. In this study, we confirmed the antagonistic interplay of ABA and IAA during the hypocotyl elongation of tomato (Solanum lycopersicum) seedlings. We identified an IAA oxidase enzyme DIOXYGENASE FOR AUXIN OXIDATION2 (SlDAO2), and its expression was induced by both external and internal ABA signals in tomato hypocotyls. Moreover, the overexpression of SlDAO2 led to a reduced sensitivity to IAA, and the knockout of SlDAO2 alleviated the inhibitory effect of ABA on hypocotyl elongation. Furthermore, an ABA‐responsive regulatory SlAREB1/SlABI3‐1/SlABI5 cascade was identified to act upstream of SlDAO2 and to precisely control its expression. SlAREB1 directly bound to the ABRE present in the SlDAO2 promoter to activate SlDAO2 expression, and SlABI3‐1 enhanced while SlABI5 inhibited the activation ability of SlAREB1 by directly interacting with SlAREB1. Our findings revealed that ABA might induce local IAA oxidation and deactivation via SlDAO2 to modulate IAA homoeostasis and thereby repress hypocotyl elongation in tomato. Summary statement: We found that ABA regulates expression of IAA oxidase gene SlDAO2 via the AREB1/ABI3‐1/ABI5 transcription factor cascade, and thereby modulating IAA homeostasis and inhibiting hypocotyl elongation in tomato seedlings. [ABSTRACT FROM AUTHOR]

In plants, glyoxalase enzymes are activated under stress conditions to mitigate the toxic effects of hyperaccumulated methylglyoxal (MG), a highly reactive carbonyl compound. Until recently, a glutathione‐dependent bi‐enzymatic pathway involving glyoxalase I (GLYI) and glyoxalase II (GLYII) was considered the primary MG‐detoxification system. Recently, a new glutathione‐independent glyoxalase III (GLYIII) mediated direct route was also reported in plants. However, the physiological significance of this new pathway remains to be elucidated across plant species. This study identified the full complement of 22 glyoxalases in tomato. Based on their strong induction under multiple abiotic stresses, SlGLYI4, SlGLYII2 and SlGLYIII2 were selected candidates for further functional characterisation. Stress‐inducible overexpression of both glutathione‐dependent (SlGLYI4 + SlGLYII2) and independent (SlGLYIII2) pathways led to enhanced tolerance in both sets of transgenic plants under abiotic stresses. However, SlGLYIII2 overexpression (OE) plants outperformed the SlGLYI4 + SlGLYII2 OE counterparts for their stress tolerance under abiotic stresses. Further, knockdown of SlGLYIII2 resulted in plants with exacerbated stress responses than those silenced for both SlGLYI4 and SlGLYII2. The superior performance of SlGLYIII2 OE tomato plants for better growth and yield under salt and osmotic treatments could be attributed to better GSH/GSSG ratio, lower reactive oxygen species levels, and enhanced antioxidant potential, indicating a prominent role of GLYIII MG‐detoxification pathway in abiotic stress mitigation in this species. Summary statement: Stress inducible overexpression of glutathione‐independent SlGLYIII2‐mediated MG‐detoxification pathway outperforms glutathione‐dependent SlGLYI4‐SlGLYII2 overexpression mediated stress tolerance by maintaining a better GSH/GSSG ratio and lower ROS levels in tomato seedlings under abiotic stresses. [ABSTRACT FROM AUTHOR]

Regulation of root transport systems is essential under fluctuating nutrient supply. In the case of potassium (K+), HAK/KUP/KT K+ transporters and voltage‐gated K+ channels ensure root K+ uptake in a wide range of K+ concentrations. In Arabidopsis, the CIPK23/CBL1‐9 complex regulates both transporter‐ and channel‐mediated root K+ uptake. However, research about K+ homeostasis in crops is in demand due to species‐specific mechanisms. In the present manuscript, we studied the contribution of the voltage‐gated K+ channel LKT1 and the protein kinase SlCIPK23 to K+ uptake in tomato plants by analysing gene‐edited knockout tomato mutant lines, together with two‐electrode voltage‐clamp experiments in Xenopus oocytes and protein–protein interaction analyses. It is shown that LKT1 is a crucial player in tomato K+ nutrition by contributing approximately 50% to root K+ uptake under K+‐sufficient conditions. Moreover, SlCIPK23 was responsible for approximately 100% of LKT1 and approximately 40% of the SlHAK5 K+ transporter activity in planta. Mg+2 and Na+ compensated for K+ deficit in tomato roots to a large extent, and the accumulation of Na+ was strongly dependent on SlCIPK23 function. The role of CIPK23 in Na+ accumulation in tomato roots was not conserved in Arabidopsis, which expands the current set of CIPK23‐like protein functions in plants. The protein kinase SlCIPK23 regulates both K+ uptake and Na+ uptake in tomato plants. By interacting with SlCBL1/9, it activates the K+ channel LKT1 and the K+ transporter SlHAK5. In addition, SlCIPK23 favours accumulation of Na+ under K+‐limiting conditions and such a role was not conserved in Arabidopsis. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are plant hormones that modulate morphological, physiological and biochemical changes as part of the acclimation strategies to phosphorus (P) deficiency, but an in‐depth description of their effects on tomato P‐acquisition strategies under P shortage is missing. Therefore, in this study, we investigate how SLs impact on root exudation and P uptake, in qualitative and quantitative terms over time, in wild‐type and SL‐depleted tomato plants grown with or without P. Under P shortage, SL‐depleted plants were unable to efficiently activate most mechanisms associated with the P starvation response (PSR), except for the up‐regulation of P transporters and increased activity of P‐solubilizing enzymes. The reduced SL biosynthesis had negative effects also under normal P provision, because plants over‐activated high‐affinity transporters and enzymatic activities (phytase, acidic phosphatase) to sustain elevated P uptake, at great carbon and nitrogen costs. A shift in the onset of PSR was also highlighted in these plants. We conclude that SLs are master kinetic regulators of the PSR in tomato and that their defective synthesis might lead both to suboptimal nutritional outcomes under P depletion and an unbalanced control of P uptake when P is available. In this study, we aimed to evaluate the role of strigolactones (SLs) in modulating a broad spectrum of phosphorus (P) acquisition and utilization strategies in tomato (Solanum lycopersicum L.) plants. Indeed, most information about SLs and P nutrition is available for the model plant Arabidopsis thaliana. Our work clearly shows that SLs silencing causes suboptimal nutritional outcomes under P depletion and unbalanced control of P uptake under P availability in tomato plants, and that SLs kinetically regulate P starvation responses in this crop. [ABSTRACT FROM AUTHOR]

Flooding is a major environmental constraint that obliges plants to adopt plastic responses in order to cope with it. When partially submerged, tomato plants undergo profound changes involving rearrangements in their morphology and metabolism. In this work, we observed that partial submergence markedly dampens root respiration and halts root growth. However, the flooded hypocotyl surprisingly enhances oxygen consumption. Previous results demonstrated that aerenchyma formation in the submerged tomato stem re‐establishes internal oxygen tension, making aerobic respiration possible. Indeed, potassium cyanide abruptly stops oxygen uptake, indicating that the cytochrome c pathway is likely to be engaged. Furthermore, we found out that leaf‐derived sugars accumulate in large amounts in hypocotyls of flooded plants. Girdling and feeding experiments point to sucrose as the main carbon source for respiration. Consistently, submerged hypocotyls are characterized by high sucrose synthase activity, indicating that sucrose is cleaved and channelled into respiration. Since inhibition of hypocotyl respiration significantly prevents sugar build‐up, it is suggested that a high respiration rate is required for sucrose unloading from phloem. As substrate availability increases, respiration is fuelled even more, leading to a maintained allocation of sugars to flooded hypocotyls. Hypocotyls of flooded tomato (Solanum lycopersicum L.) plants show increased oxygen consumption and sugar accumulation in response to root submergence. Shoot‐derived sucrose fuels respiration, which in turn sustains further sugar delivery towards the hypocotyl. [ABSTRACT FROM AUTHOR]

Although many phenylpropanoid pathway‐derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID‐4‐HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad‐spectrum resistance in higher plants without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signalling and pathogenesis‐related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root‐knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid‐degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity. Perturbation of the phenylpropanoid pathway through transient chemical inhibition of the phenylpropanoid pathway enzyme CINNAMIC ACID‐4‐HYDROXYLASE induces broad‐spectrum resistance in plants via mechanisms which include reprogramming of the phenylpropanoid and flavonoid pathways, PR protein accumulation and altered ROS metabolism. [ABSTRACT FROM AUTHOR]

Plants employ systemic‐induced resistance as part of their defence arsenal against pathogens. In recent years, the application of mild heating has been found to induce resistance against several pathogens. In the present study, we investigated the effect of root zone warming (RZW) in promoting tomato's resistance against the necrotrophic fungus Botrytis cinerea (Bc), the hemibiotrophic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) and the biotrophic fungus Oidium neolycopersici (On). We demonstrate that RZW enhances tomato's resistance to Bc, On and Xcv through a process that is dependent on salicylic acid and ethylene. RZW induced tomato immunity, resulting in increased defence gene expression, reactive oxygen species (ROS) and ethylene output when plants were challenged, even in the absence of pathogens. Overall, the results provide novel insights into the underlying mechanisms of warming‐induced immune responses against phytopathogens with different lifestyles in tomato. Plants are often exposed to several stresses simultaneously, particularly in agricultural settings; here, we investigate the relationships between heat and pathogen stresses. We demonstrate that root zone warming induces systemic immunity and promotes resistance to several tomato pathogens, through a process that is dependent on salicylic acid and ethylene. [ABSTRACT FROM AUTHOR]

Current crop protection strategies against the fungal pathogen Botrytis cinerea rely on a combination of conventional fungicides and host genetic resistance. However, due to pathogen evolution and legislation in the use of fungicides, these strategies are not sufficient to protect plants against this pathogen. Defence elicitors can stimulate plant defence mechanisms through a phenomenon known as defence priming. Priming results in a faster and/or stronger expression of resistance upon pathogen recognition by the host. This work aims to study defence priming by a commercial formulation of the elicitor chitosan. Treatments with chitosan result in induced resistance (IR) in solanaceous and brassicaceous plants. In tomato plants, enhanced resistance has been linked with priming of callose deposition and accumulation of the plant hormone jasmonic acid (JA). Large‐scale transcriptomic analysis revealed that chitosan primes gene expression at early time‐points after infection. In addition, two novel tomato genes with a characteristic priming profile were identified, Avr9/Cf‐9 rapidly elicited protein 75 (ACRE75) and 180 (ACRE180). Transient and stable over‐expression of ACRE75, ACRE180 and their Nicotiana benthamiana homologs, revealed that they are positive regulators of plant resistance against B. cinerea. This provides valuable information in the search for strategies to protect Solanaceae plants against B. cinerea. Chitosan primes cell wall defences, accumulation of defence‐related hormones and expression of Avr9/Cf‐9 rapidly elicited genes against Botrytis cinerea in Solanum lycopersicum (tomato), which provides valuable information in the search for protection strategies in Solanaceous crops. [ABSTRACT FROM AUTHOR]

Oligogalacturonides (OGs) are fragments of pectin released from the plant cell wall during insect or pathogen attack. They can be perceived by the plant as damage signals, triggering local and systemic defence responses. Here, we analyse the dynamics of local and systemic responses to OG perception in tomato roots or shoots, exploring their impact across the plant and their relevance in pathogen resistance. Targeted and untargeted metabolomics and gene expression analysis in plants treated with purified OGs revealed that local responses were transient, while distal responses were stronger and more sustained. Remarkably, changes were more conspicuous in roots, even upon foliar application of the OGs. The treatments differentially activated the synthesis of defence‐related hormones and secondary metabolites including flavonoids, alkaloids and lignans, some of them exclusively synthetized in roots. Finally, the biological relevance of the systemic defence responses activated upon OG perception was confirmed, as the treatment induced systemic resistance to Botrytis cinerea. Overall, this study shows the differential regulation of tomato defences upon OGs perception in roots and shoots and reveals the key role of roots in the coordination of the plant responses to damage sensing. Oligogalacturonide perception in tomato roots or shoots triggers differential transient local responses, but also a myriad of systemic responses at the metabolic, transcriptomic and enzymatic level leading to pathogen resistance. The results highlight the key role of roots in the regulation of these systemic responses. [ABSTRACT FROM AUTHOR]

Seed quality and seedling establishment are the most important factors affecting successful crop development. They depend on the genetic background and are acquired during seed maturation and therefor, affected by the maternal environment under which the seeds develop. There is little knowledge about the genetic and environmental factors that affect seed quality and seedling establishment. The aim of this study is to identify the loci and possible molecular mechanisms involved in acquisition of seed quality and how these are controlled by adverse maternal conditions. For this, we used a tomato recombinant inbred line (RIL) population consisting of 100 lines which were grown under two different nutritional environmental conditions, high phosphate and low nitrate. Most of the seed germination traits such as maximum germination percentage (Gmax), germination rate (t50) and uniformity (U8416) showed ample variation between genotypes and under different germination conditions. This phenotypic variation leads to identification of quantitative trait loci (QTLs) which were dependent on genetic factors, but also on the interaction with the maternal environment (QTL × E). Further studies of these QTLs may ultimately help to predict the effect of different maternal environmental conditions on seed quality and seedling establishment which will be very useful to improve the production of high‐performance seeds. The environment in which seeds develop has profound effect on seed and seedling quality. To elucidate the underlying mechanisms of this effect in tomato, we performed QTL analysis with a RIL population grown in different nutritional maternal environments and detected many QTLs which are dependent on both genetic factors and the maternal environment. [ABSTRACT FROM AUTHOR]

Root K+ acquisition is a key process for plant growth and development, extensively studied in the model plant Arabidopsis thaliana. Because important differences may exist among species, translational research supported by specific studies is needed in crops such as tomato. Here we present a reverse genetics study to demonstrate the role of the SlHAK5 K+ transporter in tomato K+ nutrition, Cs+ accumulation and its fertility. slhak5 KO lines, generated by CRISPR‐Cas edition, were characterized in growth experiments, Rb+ and Cs+ uptake tests and root cells K+‐induced plasma membrane depolarizations. Pollen viability and its K+ accumulation capacity were estimated by using the K+‐sensitive dye Ion Potassium Green 4. SlHAK5 is the major system for high‐affinity root K+ uptake required for plant growth at low K+, even in the presence of salinity. It also constitutes a pathway for Cs+ entry in tomato plants with a strong impact on fruit Cs+ accumulation. SlHAK5 also contributes to pollen K+ uptake and viability and its absence produces almost seedless fruits. Knowledge gained into SlHAK5 can serve as a model for other crops with fleshy fruits and it can help to generate tools to develop low Cs+ or seedless fruits crops. The K+ transporter SlHAK5 from tomato plays a crucial role in K+ nutrition, in particular under saline conditions, and in the accumulation of Cs+ in vegetative tissues and in fruits. Moreover, slhak5 fruits have few seeds which are related to SlHAK5 contribution to pollen K+ uptake and viability. [ABSTRACT FROM AUTHOR]

Climate change threatens food security, and plant science researchers have investigated methods of sustaining crop yield under drought. One approach has been to overproduce abscisic acid (ABA) to enhance water use efficiency. However, the concomitant effects of ABA overproduction on plant vascular system functioning are critical as it influences vulnerability to xylem hydraulic failure. We investigated these effects by comparing physiological and hydraulic responses to water deficit between a tomato (Solanum lycopersicum) wild type control (WT) and a transgenic line overproducing ABA (sp12). Under well‐watered conditions, the sp12 line displayed similar growth rate and greater water use efficiency by operating at lower maximum stomatal conductance. X‐ray microtomography revealed that sp12 was significantly more vulnerable to xylem embolism, resulting in a reduced hydraulic safety margin. We also observed a significant ontogenic effect on vulnerability to xylem embolism for both WT and sp12. This study demonstrates that the greater water use efficiency in the tomato ABA overproducing line is associated with higher vulnerability of the vascular system to embolism and a higher risk of hydraulic failure. Integrating hydraulic traits into breeding programmes represents a critical step for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under water deficit. We show that an ABA overproducing tomato line exhibits greater water use efficiency than its wild type counterpart but higher vulnerability to hydraulic failure through increased vulnerability to xylem embolism and a reduced hydraulic safety margin. This suggests that breeding programmes should integrate hydraulic traits for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under drought. [ABSTRACT FROM AUTHOR]

Silicon (Si) accumulation in shoots differs greatly with plant species, but the molecular mechanisms for this interspecific difference are unknown. Here, we isolated homologous genes of rice Si influx (SlLsi1) and efflux (SlLsi2) transporter genes in tomato (Solanum lycopersicum L.) and functionally characterized these genes. SlLsi1 showed transport activity for Si when expressed in both rice lsi1 mutant and Xenopus laevis oocytes. SlLsi1 was constitutively expressed in the roots. Immunostaining showed that SlLsi1 was localized at the plasma membrane of both root tip and basal region without polarity. Furthermore, overexpression of SlLsi1 in tomato increased Si concentration in the roots and root cell sap but did not alter the Si concentration in the shoots. By contrast, two Lsi2‐like proteins did not show efflux transport activity for Si in Xenopus oocytes. However, when functional CsLsi2 from cucumber was expressed in tomato, the Si uptake was significantly increased, resulting in higher Si accumulation in the leaves and enhanced tolerance of the leaves to water deficit and high temperature. Our results suggest that the low Si accumulation in tomato is attributed to the lack of functional Si efflux transporter Lsi2 required for active Si uptake although SlLsi1 is functional. Silicon accumulation in shoots differs greatly with plant species. Here, we found that low silicon accumulation in tomato is attributed to the lack of functional silicon efflux transporters although silicon influx transporter is functional. This work will contribute to better understanding of the molecular mechanisms for the interspecific difference in silicon accumulation. [ABSTRACT FROM AUTHOR]

Coordination between structural and physiological traits is key to plants' responses to environmental fluctuations. In heterobaric leaves, bundle sheath extensions (BSEs) increase photosynthetic performance (light‐saturated rates of photosynthesis, Amax) and water transport capacity (leaf hydraulic conductance, Kleaf). However, it is not clear how BSEs affect these and other leaf developmental and physiological parameters in response to environmental conditions. The obscuravenosa (obv) mutation, found in many commercial tomato varieties, leads to absence of BSEs. We examined structural and physiological traits of tomato heterobaric and homobaric (obv) near‐isogenic lines grown at two different irradiance levels. Kleaf, minor vein density, and stomatal pore area index decreased with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Homobaric plants, on the other hand, showed increased Amax, leaf intercellular air spaces, and mesophyll surface area exposed to intercellular airspace (Smes) in comparison with heterobaric plants when both were grown in the shade. BSEs further affected carbon isotope discrimination, a proxy for long‐term water‐use efficiency. BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating leaf structure, photosynthetic function, and water supply and demand. The presence of bundle sheath extension (BSEs) defines leaves as heterobaric, as opposed to homobaric leaves that lack them. Multiple functions have been proposed for BSEs, but their impact on different environmental conditions is still unclear. Here, we compared a tomato (Solanum lycopersicum) homobaric mutant lacking BSEs with its corresponding heterobaric wild type, grown under two irradiance conditions. We show that the presence of BSEs differentially alters various physiological and anatomical parameters in response to growth irradiance. We propose that BSEs could act as hubs coordinating leaf plasticity in response to environmental factors. [ABSTRACT FROM AUTHOR]

MicroRNA1916 (miR1916) is one of the nonconserved miRNAs that respond to various stresses in plants, but little has been known at present about its mechanisms in biotic stresses. In this study, the expression of Solanum lycopersicum (sly)‐miR1916 in tomato was found to be down‐regulated after infection with Phytophthora infestans or Botrytis cinerea. Tomato plants that overexpressed sly‐miR1916 displayed significant enhancement in susceptibility to P. infestans and B. cinerea infection, as well as increased tendency to produce reactive oxygen species. Silencing of sly‐miR1916 by short tandem target mimic and artificial microRNA strategies caused the tomato plants to become more tolerant to adverse conditions. In addition, lower sly‐miR1916 expression could up‐regulate the expression of strictosidine synthase (STR‐2), UDP‐glycosyltransferases (UGTs), late blight resistance protein homolog R1B‐16, disease resistance protein RPP13‐like, and MYB transcription factor (MYB12), which ultimately resulted in the accumulation of α‐tomatine and anthocyanins via STR‐2, UGT, and MYB12. Furthermore, ectopic expression of sly‐miR1916/STR‐2 significantly changed the tolerance of tobacco to B. cinerea. Taken together, the results demonstrated that sly‐miR1916 might regulate the expression of STR‐2, UGT, and MYB12 in tomato plant, conferring sensitivity to biotic stress via modulating α‐tomatine and anthocyanins. The sly‐miR1916 acts as negative regulator of defense responses against Phytophthora infestans and Botrytis cinerea infection via modulating STR‐2, UGT, R1B‐16, RPP13‐like and MYB12, α‐tomatine and anthocyanins. [ABSTRACT FROM AUTHOR]

Abstract: The production of anthocyanin is regulated by light and corresponding photoreceptors. In this study, we found that exposure to blue light and overexpression of CRY1a are associated with increased accumulation of anthocyanin in tomato (Solanum lycopersicum L.). These responses are the result of changes in mRNA and the protein levels of SlHY5, which is a transcription factor. In vitro and in vivo experiments using electrophoretic mobility shift assay and ChIP‐qPCR assays revealed that SlHY5 could directly recognize and bind to the G‐box and ACGT‐containing element in the promoters of anthocyanin biosynthesis genes, such as chalcone synthase 1, chalcone synthase 2, and dihydroflavonol 4‐reductase. Silencing of SlHY5 in OE‐CRY1a lines decreased the accumulation of anthocyanin. The findings presented here not only deepened our understanding of how light controls anthocyanin biosynthesis and associated photoprotection in tomato leaves, but also allowed us to explore potential targets for improving pigment production. [ABSTRACT FROM AUTHOR]

Abstract: Interplay of hormones with reactive oxygen species (ROS) fine‐tunes the response of plants to stress; however, the crosstalk between brassinosteroids (BRs) and ROS in nematode resistance is unclear. In this study, we found that low BR biosynthesis or lack of BR receptor increased, whilst exogenous BR decreased the susceptibility of tomato plants to Meloidogyne incognita. Hormone quantification coupled with hormone mutant complementation experiments revealed that BR did not induce the defence response by triggering salicylic acid (SA), jasmonic acid/ethylene (JA/ET) or abscisic acid (ABA) signalling pathway. Notably, roots of BR‐deficient plants had decreased apoplastic ROS accumulation, transcript of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1) and WHITEFLY INDUCED1 (WFI1), and reduced activation of mitogen‐activated protein kinase 1/2 (MPK1/2) and MPK3. Silencing of RBOH1, WFI1, MPK1, MPK2 and MPK3 all increased the root susceptibility to nematode and attenuated BR‐induced resistance against the nematode. Significantly, suppressed transcript of RBOH1 compromised BR‐induced activation of MPK1/2 and MPK3. These results strongly suggest that RBOH‐dependent MPK activation is involved in the BR‐induced systemic resistance against the nematode. [ABSTRACT FROM AUTHOR]

Abstract: Despite being essential for C3 plants, photorespiration is believed to cause a significant crop yield loss even under future climates. However, how photorespiration affects plant basal defence still remains largely unknown. Here, we studied the involvement of photorespiration in tomato–Pseudomonas syringae pv. tomato DC3000 interaction focusing on three photorespiratory genes. Inoculation with P. syringae increased photorespiration rate (Pr) and expression of glycolate oxidase (GOX2), serine glyoxylate aminotransferase (SGT) and serine hydroxyl methyltransferase (SHMT1); however, inhibition of photorespiration by isonicotinic acid hydrazide decreased tomato basal defence against P. syringae. Furthermore, silencing of GOX2, SGT or SHMT1 genes in tomato decreased Pr but increased susceptibility to P. syringae, whereas transient overexpression of GOX2, SGT or SHMT1 in tobacco increased basal defence. Further study revealed that salicylic acid (SA) signalling is involved in GOX2‐mediated, SGT‐mediated and SHMT1‐mediated defence. Moreover, H2O2 pretreatment remarkably alleviated the GOX2 silencing‐induced depression in basal defence and SA signalling, whereas it had no effect on that of SGT‐silenced and SHMT1‐silenced plants. Taken together, these results suggest that H2O2 is critical for GOX2‐modulated but not SGT‐modulated or SHMT1‐modulated SA signalling and subsequent basal defence against P. syringae. This work deepens the understanding of photorespiration‐involved defence responses to bacterial attack in plants. [ABSTRACT FROM AUTHOR]

Excessive soil salinity diminishes crop yield and quality. In a previous study in tomato, we identified two closely linked genes encoding HKT1-like transporters, HKT1; 1 and HKT1; 2, as candidate genes for a major quantitative trait locus ( kc7. 1) related to shoot Na+/K+ homeostasis - a major salt tolerance trait - using two populations of recombinant inbred lines (RILs). Here, we determine the effectiveness of these genes in conferring improved salt tolerance by using two near-isogenic lines (NILs) that were homozygous for either the Solanum lycopersicum allele (NIL17) or for the Solanum cheesmaniae allele (NIL14) at both HKT1 loci; transgenic lines derived from these NILs in which each HKT1; 1 and HKT1; 2 had been silenced by stable transformation were also used. Silencing of ScHKT1; 2 and SlHKT1; 2 altered the leaf Na+/K+ ratio and caused hypersensitivity to salinity in plants cultivated under transpiring conditions, whereas silencing SlHKT1; 1/ ScHKT1; 1 had a lesser effect. These results indicate that HKT1; 2 has the more significant role in Na+ homeostasis and salinity tolerance in tomato. [ABSTRACT FROM AUTHOR]

Low temperature is a major environmental stress that seriously compromises plant development, distribution and productivity. Most crops are from tropical origin and, consequently, chilling sensitive. Interestingly, however, some tropical plants, are able to augment their chilling tolerance when previously exposed to suboptimal growth temperatures. Yet, the molecular and physiological mechanisms underlying this adaptive process, termed chilling acclimation, still remain practically unknown. Here, we demonstrate that tomato plants can develop a chilling acclimation response, which includes comprehensive transcriptomic and metabolic adjustments leading to increased chilling tolerance. More important, our results reveal strong resemblances between this response and cold acclimation, the process whereby plants from temperate regions raise their freezing tolerance after exposure to low, non-freezing temperatures. Both chilling and cold acclimation are regulated by a similar set of transcription factors and hormones, and share common defence mechanisms, including the accumulation of compatible solutes, the mobilization of antioxidant systems and the rearrangement of the photosynthetic machinery. Nonetheless, we have found some important divergences that may account for the freezing sensitivity of tomato plants. The data reported in this manuscript should foster new research into the chilling acclimation response with the aim of improving tomato tolerance to low temperature. [ABSTRACT FROM AUTHOR]

Ascorbate is oxidized into the radical monodehydroascorbate (MDHA) through ascorbate oxidase or peroxidase activity or non-enzymatically by reactive oxygen species. Regeneration of ascorbate from MDHA is ensured by the enzyme MDHA reductase (MDHAR). Previous work has shown that growth processes and yield can be altered by modifying the activity of enzymes that recycle ascorbate; therefore, we have studied similar processes in cherry tomato ( Solanum lycopersium L.) under- or overexpressing MDHAR. Physiological and metabolic characterization of these lines was carried out under different light conditions or by manipulating the source-sink ratio. Independently of the light regime, slower early growth of all organs was observed in MDHAR silenced lines, decreasing final fruit yield. Photosynthesis was altered as was the accumulation of hexoses and sucrose in a light-dependent manner in plantlets. Sucrose accumulation was also repressed in young fruits and final yield of MDHAR silenced lines showed a stronger decrease under carbon limitation, and the phenotype was partially restored by reducing fruit load. Ascorbate and MDHA appear to be involved in control of growth and sugar metabolism in cherry tomato and the associated enzymes could be potential targets for yield improvement. [ABSTRACT FROM AUTHOR]

Recently, contradicting evidence has been reported on the contribution of xylem and phloem influx into tomato fruits, urging the need for a better understanding of the mechanisms involved in fruit growth. So far, little research has been performed on quantifying the effect of light intensity on the different contributors to the fruit water balance. However, as light intensity affects both transpiration and photosynthesis, it might be expected to induce important changes in the fruit water balance. In this study, tomato plants ( S olanum lycopersicum L.) were grown in light and shade conditions and the fruit water balance was studied by measuring fruit growth of girdled and intact fruits with linear variable displacement transducers combined with a model-based approach. Results indicated that the relative xylem contribution significantly increased when shading lowered light intensity. This resulted from both a higher xylem influx and a lower phloem influx during the daytime. Plants from the shade treatment were able to maintain a stronger gradient in total water potential between stem and fruits during daytime, thereby promoting xylem influx. It appeared that the xylem pathway was still functional at 35 days after anthesis and that relative xylem contribution was strongly affected by environmental conditions. [ABSTRACT FROM AUTHOR]

γ-Aminobutyric acid ( GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway ( GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases ( SlGADs), GABA transaminases ( SlGABA - T s) and succinic semialdehyde dehydrogenase ( SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs ( GABA biosynthetic genes) and SlGABA - T s ( GABA catabolic genes) led to increased accumulation of reactive oxygen species ( ROS) as well as salt sensitivity under 200 m m NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA - T s-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to γ-hydroxybutyrate as reported previously in A rabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and γ-hydroxybutyrate and subsequent ROS accumulation under salt stress. [ABSTRACT FROM AUTHOR]