Meiotic instability and irregular chromosome pairing underpin heat-induced infertility in bread wheat carrying the Rht-B1b or Rht-D1b Green Revolution genes

Mutations in the Rht-B1a and Rht-D1a genes of wheat (Triticum aestivum; resulting in Rht-B1b and Rht-D1b alleles) cause gibberellin-insensitive dwarfism and are one of the most important elements of increased yield introduced during the 'Green Revolution'. We measured the effects of a short period of heat imposed during the early reproductive stage on near-isogenic lines carrying Rht-B1b or Rht-D1b alleles, with respect to the wild-type (WT). The temperature shift caused a significant fertility loss within the ears of Rht-B1b and Rht-D1b wheats, greater than that observed for the WT. Defects in chromosome synapsis, reduced homologous recombination and a high frequency of chromosome mis-segregation were associated with reduced fertility. The transcription of TaGA3ox gene involved in the final stage of gibberellic acid (GA) biosynthesis was activated and ultra-performance liquid chromatography-tandem mass spectrometry identified GA1 as the dominant bioactive GA in developing ears, but levels were unaffected by the elevated temperature. Rht-B1b and Rht-D1b mutants were inclined to meiotic errors under optimal temperatures and showed a higher susceptibility to heat than their tall counterparts. Identification and introduction of new dwarfing alleles into modern breeding programmes is invaluable in the development of climate-resilient wheat varieties.

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.

Global transcriptome and targeted metabolite analyses of roots reveal different defence mechanisms against Ralstonia solanacearum infection in two resistant potato cultivars

Ralstonia solanacearum (Rs), the causal agent of bacterial wilt disease in an unusually wide range of host plants, including potato (Solanum tuberosum), is one of the most destructive phytopathogens that seriously reduces crop yields worldwide. Identification of defence mechanisms underlying bacterial wilt resistance is a prerequisite for biotechnological approaches to resistance breeding. Resistance to Rs has been reported only in a few potato landraces and cultivars. Our in vitro inoculation bioassays confirmed that the cultivars 'Calalo Gaspar' (CG) and 'Cruza 148' (CR) are resistant to Rs infection. Comparative transcriptome analyses of CG and CR roots, as well as of the roots of an Rs-susceptible cultivar, 'Désirée' (DES), were carried out two days after Rs infection, in parallel with their respective noninfected controls. In CR and DES, the upregulation of chitin interactions and cell wall-related genes was detected. The phenylpropanoid biosynthesis and glutathione metabolism pathways were induced only in CR, as confirmed by high levels of lignification over the whole stele in CR roots six days after Rs infection. At the same time, Rs infection greatly increased the concentrations of chlorogenic acid and quercetin derivatives in CG roots as it was detected using ultra-performance liquid chromatography - tandem mass spectrometry. Characteristic increases in the expression of MAP kinase signalling pathway genes and in the concentrations of jasmonic, salicylic, abscisic and indoleacetic acid were measured in DES roots. These results indicate different Rs defence mechanisms in the two resistant potato cultivars and a different response to Rs infection in the susceptible cultivar.

Volatile organic compounds shape belowground plant-fungi interactions

Volatile organic compounds (VOCs), a bouquet of chemical compounds released by all life forms, play essential roles in trophic interactions. VOCs can facilitate a large number of interactions with different organisms belowground. VOCs-regulated plant-plant or plant-insect interaction both below and aboveground has been reported extensively. Nevertheless, there is little information about the role of VOCs derived from soilborne pathogenic fungi and beneficial fungi, particularly mycorrhizae, in influencing plant performance. In this review, we show how plant VOCs regulate plant-soilborne pathogenic fungi and beneficial fungi (mycorrhizae) interactions. How fungal VOCs mediate plant-soilborne pathogenic and beneficial fungi interactions are presented and the most common methods to collect and analyze belowground volatiles are evaluated. Furthermore, we suggest a promising method for future research on belowground VOCs.

D27-LIKE1 isomerase has a preference towards trans/cis and cis/cis conversions of carotenoids in Arabidopsis

Carotenoids contribute to a variety of physiological processes in plants, functioning also as biosynthesis precursors of ABA and strigolactones (SLs). SL biosynthesis starts with the enzymatic conversion of all-trans-β-carotene to 9-cis-β-carotene by the DWARF27 (D27) isomerase. In Arabidopsis, D27 has two closely related paralogs, D27-LIKE1 and D27-LIKE2, which were predicted to be β-carotene-isomerases. In the present study, we characterised D27-LIKE1 and identified some key aspects of its physiological and enzymatic functions in Arabidopsis. d27-like1-1 mutant does not display any strigolactone-deficient traits and exhibits a substantially higher 9-cis-violaxanthin content, which is accompanied by a slightly higher ABA level. In vitro feeding assays with recombinant D27-LIKE1 revealed that the protein exhibits affinity to all β-carotene isoforms but with an exclusive preference towards trans/cis conversions and the interconversion between 9-cis, 13-cis and 15-cis-β-carotene forms, and accepts zeaxanthin and violaxanthin as substrates. Finally, we present evidence showing that D27-LIKE1 mRNA is phloem mobile and D27-LIKE1 is an ancient isomerase with a long evolutionary history. In summary, we demonstrate that D27-LIKE1 is a carotenoid isomerase with multi-substrate specificity and has a characteristic preference towards the catalysation of cis/cis interconversion of carotenoids. Therefore, D27-LIKE1 is a potential regulator of carotenoid cis pools and, eventually, SL and ABA biosynthesis pathways.

Redox and Hormonal Changes in the Transcriptome of Grape (Vitis vinifera) Berries during Natural Noble Rot Development

Noble rot is a favorable form of the interaction between grape (Vitis spp.) berries and the phytopathogenic fungus Botrytis cinerea. The transcriptome pattern of grapevine cells subject to natural noble rot development in the historic Hungarian Tokaj wine region has not been previously published. Furmint, a traditional white Tokaj variety suited to develop great quality noble rot was used in the experiments. Exploring a subset of the Furmint transcriptome redox and hormonal changes distinguishing between noble rot and bunch rot was revealed. Noble rot is defined by an early spike in abscisic acid (ABA) accumulation and a pronounced remodeling of ABA-related gene expression. Transcription of glutathione S-transferase isoforms is uniquely upregulated, whereas gene expression of some sectors of the antioxidative apparatus (e.g., catalases, carotenoid biosynthesis) is downregulated. These mRNA responses are lacking in berries exposed to bunch rot. Our results help to explain molecular details behind the fine and dynamic balance between noble rot and bunch rot development.

Methylglyoxal induces stress signaling and promotes the germination of maize at low temperature

Maize is sensitive to cold injury, especially during germination. Since cold causes oxidative stress, compounds that promote the accumulation of free radical forms, such as the reactive aldehyde (RA) methylglyoxal (MG), may be suitable to trigger a systemic defense response. In this study, maize seeds were soaked in MG solution for one night at room temperature, before germination test at 13°C. The exogenous MG enhanced the germination and photosynthetic performance of maize at low temperature. Transcriptome analysis, hormonal, and flavonoid profiling indicated MG-induced changes in photosystem antenna proteins, pigments, late embryogenesis abundant proteins, abscisic acid (ABA) derivatives, chaperons, and certain dihydroflavonols, members of the phenylpropanoid pathway. MG-response of the two maize cultivars (A654 and Cm174) were somewhat different, but we recorded higher endogenous hydrogen peroxide (H₂ O₂ ) and lower nitric oxide (NO) level in at least one of the treated genotypes. These secondary signal molecules may provoke some of the changes in the hormonal, metabolic and gene expression profile. Decreased auxin transport, but increased ABA degradation and cytokinin and jasmonic acid (JA) synthesis, as well as an altered carbohydrate metabolism and transport (amylases, invertases, and SWEET transporters) could have promoted germination of MG-pretreated seeds. While LEA accumulation could have protected against osmotic stress and catalase expression and production of many antioxidants, like para-hydroxybenzoic acid (p-HBA) and anthocyanins may have balanced the oxidative environment for maize germination. Our results showed that MG-pretreatment could be an effective way to promote cold germination and its effect was more pronounced in the originally cold-sensitive maize genotype.

Activation of Local and Systemic Defence Responses by Flg22 Is Dependent on Daytime and Ethylene in Intact Tomato Plants

The first line of plant defence responses against pathogens can be induced by the bacterial flg22 and can be dependent on various external and internal factors. Here, we firstly studied the effects of daytime and ethylene (ET) using Never ripe (Nr) mutants in the local and systemic defence responses of intact tomato plants after flg22 treatments. Flg22 was applied in the afternoon and at night and rapid reactions were detected. The production of hydrogen peroxide and nitric oxide was induced by flg22 locally, while superoxide was induced systemically, in wild type plants in the light period, but all remained lower at night and in Nr leaves. Flg22 elevated, locally, the ET, jasmonic acid (JA) and salicylic acid (SA) levels in the light period; these levels did not change significantly at night. Expression of Pathogenesis-related 1 (PR1), Ethylene response factor 1 (ERF1) and Defensin (DEF) showed also daytime- and ET-dependent changes. Enhanced ERF1 and DEF expression and stomatal closure were also observable in systemic leaves of wild type plants in the light. These data demonstrate that early biotic signalling in flg22-treated leaves and distal ones is an ET-dependent process and it is also determined by the time of day and inhibited in the early night phase.

Molecular background of cadmium tolerance in Rht dwarf wheat mutant is related to a metabolic shift from proline and polyamine to phytochelatin synthesis

Plant height is among the most important agronomic traits influencing crop yield. Wheat lines carrying Rht genes are important in plant breeding due to their both higher yield capacity and better tolerance to certain environmental stresses. However, the effects of dwarf-inducing genes on stress acclimation mechanisms are still poorly understood. Under the present conditions, cadmium stress induced different stress responses and defence mechanisms in the wild-type and dwarf mutant, and the mutant with the Rht-B1c allele exhibited higher tolerance. In the wild type after cadmium treatment, the abscisic acid synthesis increased in the leaves, which in turn might have induced the polyamine and proline metabolisms in the roots. However, in the mutant line, the slight increment in the leaf abscisic acid content accompanied by relatively high salicylic acid accumulation was not sufficient to induce such a great accumulation of proline and putrescine. Although changes in proline and polyamines, especially putrescine, showed similar patterns, the accumulation of these compounds was antagonistically related to the phytochelatin synthesis in the roots of the wild type after cadmium stress. In the dwarf genotype, a favourable metabolic shift from the synthesis of polyamine and proline to that of phytochelatin was responsible for the higher cadmium tolerance observed.

Polyamine-Induced Hormonal Changes in eds5 and sid2 Mutant Arabidopsis Plants

Polyamines are multifaceted compounds which play a role in regulating plant growth and stress tolerance in interactions with plant hormones. The aim of the present study was to reveal how exogenous polyamines influence the synthesis of salicylic acid, with a special emphasis on the effect of salicylic acid deficiency on the polyamine metabolism and polyamine-induced changes in other plant hormone contents. Our hypothesis was that the individual polyamines induced different changes in the polyamine and salicylic acid metabolism of the wild type and salicylic acid-deficient Arabidopsis mutants, which in turn influenced other hormones. To our knowledge, such a side-by-side comparison of the influence of eds5-1 and sid2-2 mutations on polyamines has not been reported yet. To achieve our goals, wild and mutant genotypes were tested after putrescine, spermidine or spermine treatments. Polyamine and plant hormone metabolism was investigated at metabolite and gene expression levels. Individual polyamines induced different changes in the Arabidopsis plants, and the responses were also genotype-dependent. Polyamines upregulated the polyamine synthesis and catabolism, and remarkable changes in hormone synthesis were found especially after spermidine or spermine treatments. The sid2-2 mutant showed pronounced differences compared to Col-0. Interactions between plant hormones may also be responsible for the observed differences.

Role of polyamines in plant growth regulation of Rht wheat mutants

Besides their protective role, polyamines also serve as signalling molecules. However, further studies are needed to elucidate the polyamine signalling pathways, especially to identify polyamine-regulated mechanisms and their connections with other regulatory molecules. Reduced height (Rht) genes in wheat are often used in breeding programs to increase harvest index. Some of these genes are encoding DELLA proteins playing role in gibberellic acid signalling. The aim of the present paper was to reveal how the mutations in Rht gene modify the polyamine-regulated processes in wheat. Wild type and two Rht mutant genotypes (Rht 1: semi-dwarf; Rht 3: dwarf mutants) were treated with polyamines. Polyamine treatments differently influenced the polyamine metabolism, the plant growth parameters and certain hormone levels (salicylic acid and abscisic acid) in these genotypes. The observed distinct metabolism of Rht 3 may more likely reflect more intensive polyamine exodus from putrescine to spermidine and spermine, and the catabolism of the higher polyamines. The lower root to shoot translocation of putrescine can contribute to the regulation of polyamine pool, which in turn may be responsible for the observed lack of growth inhibition in Rht 3 after spermidine and spermine treatments. Lower accumulation of salicylic acid and abscisic acid, plant hormones usually linked with growth inhibition, in leaves may also be responsible for the diminished negative effect of higher polyamines on the shoot growth parameters observed in Rht 3. These results provide an insight into the role of polyamines in plant growth regulation based on the investigation of gibberellin-insensitive Rht mutants.

Metabolic response to drought in six winter wheat genotypes

Wheat is one of the most important cereals, whose growth and development is strongly limited by drought. This study investigated the physiological and metabolic response of six winter wheat cultivars to drought with the emphasis on the induction of dominant metabolites affected by the treatment and genotypes or both. The plants were exposed to a moderate (non-lethal) drought stress, which was induced by withholding watering for six days under controlled greenhouse conditions. A decline in CO2 assimilation (Pn) and transpiration rate, stomata closure, a decrease in relative water content (RWC) and increase of malondialdehyde content were observed in drought-treated plants of all cultivars. These changes were most pronounced in Ellvis, while Soissons was able to retain the higher RWC and Pn. Among the studied metabolites, sugars (sucrose, glucose, fructose, several disaccharides), organic acids (malic acid, oxalic acids), amino acids (proline, threonine, gamma-aminobutyric acid (GABA), glutamine) and sugar alcohols such as myo-inositol accumulated to higher levels in the plants exposed to drought stress in comparison with the control. The accumulation of several metabolites in response to drought differed between the genotypes. Drought induced the production of sucrose, malic acid and oxalic acid, unknown organic acid 1, unknown disaccharide 1, 2 and 3, GABA, L-threonine, glutamic acid in four (Soissons, Žitarka, Antonija or Toborzó) out of six genotypes. In addition, Soissons, which was the most drought tolerant genotype, accumulated the highest amount of unknown disaccharide 5, galactonic and phosphoric acids. The two most drought sensitive cultivars, Srpanjka and Ellvis, demonstrated different metabolic adjustment in response to the stress treatment. Srpanjka responded to drought by increasing the amount of glucose and fructose originated from hydrolyses of sucrose and accumulating unidentified sugar alcohols 1 and 2. In Ellvis, drought caused inhibition of photosynthetic carbon metabolism, as evidence by the decreased Pn, gs, RWC and accumulation levels of sugar metabolites (sucrose, glucose and fructose). The results revealed the differences in metabolic response to drought among the genotypes, which drew attention on metabolites related with general response and on those metabolites which are part of specific response that may play an important role in drought tolerance.

The effects of putrescine are partly overlapping with osmotic stress processes in wheat

Polyamine metabolism is in relation with several metabolic pathways and linked with plant hormones or signalling molecules; in addition polyamines may modulate the up- or down-regulation of gene expression. However the precise mechanism by which polyamines act at the transcription level is still unclear. In the present study the modifying effect of putrescine pre-treatment has been investigated using the microarray transcriptome profile analysis under the conditions where exogenous putrescine alleviated osmotic stress in wheat plants. Pre-treatment with putrescine induced the unique expression of various general stress-related genes. Although there were obvious differences between the effects of putrescine and polyethylene glycol treatments, there was also a remarkable overlap between the effects of putrescine and osmotic stress responses in wheat plants, suggesting that putrescine has already induced acclimation processes under control conditions. The fatty acid composition in certain lipid fractions and the antioxidant enzyme activities have also been specifically changed under osmotic stress conditions or after treatment with putrescine.