Stress-induced co-expression of two alternative oxidase (VuAox1 and 2b) genes in Vigna unguiculata

Alternative Oxidase: From Molecule and Function to Future Inhibitors

In the respiratory chain of the majority of aerobic organisms, the enzyme alternative oxidase (AOX) functions as the terminal oxidase and has important roles in maintaining metabolic and signaling homeostasis in mitochondria. AOX endows the respiratory system with flexibility in the coupling among the carbon metabolism pathway, electron transport chain (ETC) activity, and ATP turnover. AOX allows electrons to bypass the main cytochrome pathway to restrict the generation of reactive oxygen species (ROS). The inhibition of AOX leads to oxidative damage and contributes to the loss of adaptability and viability in some pathogenic organisms. Although AOXs have recently been identified in several organisms, crystal structures and major functions still need to be explored. Recent work on the trypanosome alternative oxidase has provided a crystal structure of an AOX protein, which contributes to the structure-activity relationship of the inhibitors of AOX. Here, we review the current knowledge on the development, structure, and properties of AOXs, as well as their roles and mechanisms in plants, animals, algae, protists, fungi, and bacteria, with a special emphasis on the development of AOX inhibitors, which will improve the understanding of respiratory regulation in many organisms and provide references for subsequent studies of AOX-targeted inhibitors.

Crop Wild Relatives: A Valuable Source of Tolerance to Various Abiotic Stresses

Global climate change is one of the major constraints limiting plant growth, production, and sustainability worldwide. Moreover, breeding efforts in the past years have focused on improving certain favorable crop traits, leading to genetic bottlenecks. The use of crop wild relatives (CWRs) to expand genetic diversity and improve crop adaptability seems to be a promising and sustainable approach for crop improvement in the context of the ongoing climate challenges. In this review, we present the progress that has been achieved towards CWRs exploitation for enhanced resilience against major abiotic stressors (e.g., water deficiency, increased salinity, and extreme temperatures) in crops of high nutritional and economic value, such as tomato, legumes, and several woody perennial crops. The advances in -omics technologies have facilitated the elucidation of the molecular mechanisms that may underlie abiotic stress tolerance. Comparative analyses of whole genome sequencing (WGS) and transcriptomic profiling (RNA-seq) data between crops and their wild relative counterparts have unraveled important information with respect to the molecular basis of tolerance to abiotic stressors. These studies have uncovered genomic regions, specific stress-responsive genes, gene networks, and biochemical pathways associated with resilience to adverse conditions, such as heat, cold, drought, and salinity, and provide useful tools for the development of molecular markers to be used in breeding programs. CWRs constitute a highly valuable resource of genetic diversity, and by exploiting the full potential of this extended allele pool, new traits conferring abiotic-stress tolerance may be introgressed into cultivated varieties leading to superior and resilient genotypes. Future breeding programs may greatly benefit from CWRs utilization for overcoming crop production challenges arising from extreme environmental conditions.

Genome-wide identification of AOX family genes in Moso bamboo and functional analysis of PeAOX1b_2 in drought and salinity stress tolerance

Five PeAOX genes from Moso bamboo genome were identified. PeAOX1b_2-OE improved tolerance to drought and salinity stress in Arabidopsis, indicating it is involved in positive regulation of abiotic stress response. Mitochondrial alternative oxidase (AOX), the important respiratory terminal oxidase in organisms, catalyzes the energy wasteful cyanide (CN)-resistant respiration, which can improve abiotic stresses tolerance and is considered as one of the functional markers for plant resistance breeding. Here, a total of five putative AOX genes (PeAOXs) were identified and characterized in a monocotyledonous woody grass Moso bamboo (Phyllostachys edulis). Phylogenetic analysis revealed that PeAOXs belonged to AOX1 subfamily, and were named PeAOX1a_1, PeAOX1a_2, PeAOX1b_1, PeAOX1b_2 and PeAOX1c, respectively. Evolutionary and divergence patterns analysis revealed that the PeAOX, OsAOX, and BdAOX families experienced positive purifying selection and may have undergone a large-scale duplication event roughly 1.35-155.90 million years ago. Additionally, the organ-specific expression analysis showed that 80% of PeAOX members were mainly expressed in leaf. Promoter sequence analysis of PeAOXs revealed cis-acting regulatory elements (CAREs) responding to abiotic stress. Most PeAOX genes were significantly upregulated after methyl jasmonate (MeJA) and abscisic acid (ABA) treatment. Moreover, under salinity and drought stresses, the ectopic overexpression of PeAOX1b_2 in Arabidopsis enhanced seed germination and seedling establishment, increased the total respiratory rate and the proportion of AOX respiratory pathway in leaf, and enhanced antioxidant ability, suggesting that PeAOX1b_2 is crucial for abiotic stress resistance in Moso bamboo.

Overexpression of Cerasus humilis ChAOX2 improves the tolerance of Arabidopsis to salt stress

Alternative oxidase (AOX) has a well-established involvement in plant growth and stress tolerance in many studies. In this study, we isolated and characterized the AOX2 from Cerasus humilis. The ChAOX2 Open Reading Frame (ORF) contains 1029 nucleotides and encodes 342 amino acid residues. The inferred amino acid sequence of ChAOX2 shared the highest sequence similarity with a homolog from Prunus yedoensis. The ChAOX2 transcripts were relatively abundant in the old leaves and significantly up-regulated by salt stress. Subcellular localization analysis showed that ChAOX2 was located in the mitochondria. We transformed ChAOX2 into wild-type Arabidopsis thaliana and found that compared with wild-type and aox mutant lines, heterotopic expression of ChAOX2 increased proline content, and peroxidase and superoxide dismutase activities, while decreasing relative conductivity and the reactive oxygen species level. Further, the ratio of alternate respiration to the total respiration in plants that overexpressed ChAOX2 was significantly higher than that in wild-type and mutant plants under salt stress. These results indicate that ChAOX2 plays a key role in salt tolerance.

Identification and characterization of a natural SNP variant in ALTERNATIVE OXIDASE gene associated with cold stress tolerance in watermelon

Alternative oxidase (AOX) is a mitochondrial enzyme encoded by a small nuclear gene family, which contains the two subfamilies, AOX1 and AOX2. In the present study on watermelon (Citrullus lanatus), only one ClAOX gene, belonging to AOX2 subfamily but having a similar gene structure to AtAOX1a, was found in the watermelon genome. The expression analysis suggested that ClAOX had the constitutive expression feature of AOX2 subfamily, but was cold inducible, which is normally considered an AOX1 subfamily feature. Moreover, one single nucleotide polymorphism (SNP) in ClAOX sequence, which led to the change from Lys (N) to Asn (K) in the 96^th amino acids, was found among watermelon subspecies. Ectopic expression of two ClAOX alleles in the Arabidopsis aox1a knock-out mutant indicated that ClAOX^K-expressing plants had stronger cold tolerance than aox1a mutant and ClAOX^N-expressing plants. Our findings suggested watermelon genome contained a single ClAOX that possessed the expression features of both AOX1 and AOX2 subfamilies. A naturally existing SNP in ClAOX differentiated the cold tolerance of transgenic Arabidopsis plants, impling a possibility this gene might be a functional marker for stress-tolerance breeding.

Molecular characterization and gene expression modulation of the alternative oxidase in a scuticociliate parasite by hypoxia and mitochondrial respiration inhibitors

Philasterides dicentrarchi is a marine benthic microaerophilic scuticociliate and an opportunistic endoparasite that can infect and cause high mortalities in cultured turbot (Scophthalmus maximus). In addition to a cytochrome pathway (CP), the ciliate can use a cyanide-insensitive respiratory pathway, which indicates the existence of an alternative oxidase (AOX) in the mitochondrion. Although AOX activity has been described in P. dicentrarchi, based on functional assay results, genetic evidence of the presence of AOX in the ciliate has not previously been reported. In this study, we conducted genomic and transcriptomic analysis of the ciliate and identified the AOX gene and its corresponding mRNA. The AOX gene (size 1,106 bp) contains four exons and three introns that generate an open reading frame of 915 bp and a protein with a predicted molecular weight of 35.6 kDa. The amino acid (aa) sequence of the AOX includes an import signal peptide targeting the mitochondria and the protein is associated with the inner membrane of the mitochondria. Bioinformatic analysis predicted that the peptide is a homodimeric glycoprotein, although monomeric forms may also appear under native conditions, with EXXH motifs associated with the diiron active centers. The aa sequences of the AOX of different P. dicentrarchi isolates are highly conserved and phylogenetically closely related to AOXs of other ciliate species, especially scuticociliates. AOX expression increased significantly during infection in the host and after the addition of CP inhibitors. This confirms the important physiological roles of AOX in respiration under conditions of low levels of O₂ and in protecting against oxidative stress generated during infection in the host.

Effects of Salicylic Acid on the Metabolism of Mitochondrial Reactive Oxygen Species in Plants

Different abiotic and biotic stresses lead to the production and accumulation of reactive oxygen species (ROS) in various cell organelles such as in mitochondria, resulting in oxidative stress, inducing defense responses or programmed cell death (PCD) in plants. In response to oxidative stress, cells activate various cytoprotective responses, enhancing the antioxidant system, increasing the activity of alternative oxidase and degrading the oxidized proteins. Oxidative stress responses are orchestrated by several phytohormones such as salicylic acid (SA). The biomolecule SA is a key regulator in mitochondria-mediated defense signaling and PCD, but the mode of its action is not known in full detail. In this review, the current knowledge on the multifaceted role of SA in mitochondrial ROS metabolism is summarized to gain a better understanding of SA-regulated processes at the subcellular level in plant defense responses.

Nitric Oxide Improves the Tolerance of Pleurotus ostreatus to Heat Stress by Inhibiting Mitochondrial Aconitase

Heat stress is one of the abiotic stresses that affect the growth and development of edible fungi. Our previous study found that exogenous NO had a protective effect on mycelia under heat stress. However, its regulatory mechanism had not been elucidated. In this study, we found that NO altered the respiratory pathway of mycelia under heat stress by regulating aco. The results have enhanced our understanding of NO signaling pathways in P. ostreatus.

Pleurotus ostreatus is widely cultivated in China. However, its cultivation is strongly affected by seasonal temperature changes, especially the high temperatures of summer. Nitric oxide (NO) was previously reported to alleviate oxidative damage to mycelia by regulating trehalose. In this study, we found that NO alleviated oxidative damage to P. ostreatus mycelia by inhibiting the protein and gene expression of aconitase (ACO), and additional studies found that the overexpression and interference of aco could affect the content of citric acid (CA). Furthermore, the addition of exogenous CA can induce alternative oxidase (aox) gene expression under heat stress, reduce the content of H₂O₂ in mycelium, and consequently protect the mycelia under heat stress. An additional analysis focused on the function of the aox gene in the heat stress response of mycelia. The results show that the colony diameter of the aox overexpression (OE-aox) strains was significantly larger than that of the wild-type (WT) strain under heat stress (32°C). In addition, the mycelia of OE-aox strains showed significantly enhanced tolerance to H₂O₂. In conclusion, this study demonstrates that NO can affect CA accumulation by regulating aco gene and ACO protein expression and that CA can induce aox gene expression and thereby be a response to heat stress.

IMPORTANCE Heat stress is one of the abiotic stresses that affect the growth and development of edible fungi. Our previous study found that exogenous NO had a protective effect on mycelia under heat stress. However, its regulatory mechanism had not been elucidated. In this study, we found that NO altered the respiratory pathway of mycelia under heat stress by regulating aco. The results have enhanced our understanding of NO signaling pathways in P. ostreatus.

Genomic structure and expression of alternative oxidase genes in legumes

Mitochondria isolated from chickpea (Cicer arietinum) possess substantial alternative oxidase (AOX) activity, even in non-stressed plants, and one or two AOX protein bands were detected immunologically, depending on the organ. Four different AOX isoforms were identified in the chickpea genome: CaAOX1 and CaAOX2A, B and D. CaAOX2A was the most highly expressed form and was strongly expressed in photosynthetic tissues, whereas CaAOX2D was found in all organs examined. These results are very similar to those of previous studies with soybean and siratro. Searches of available databases showed that this pattern of AOX genes and their expression was common to at least 16 different legume species. The evolution of the legume AOX gene family is discussed, as is the in vivo impact of an inherently high AOX capacity in legumes on growth and responses to environmental stresses.

Genome-wide identification and characterization of ALTERNATIVE OXIDASE genes and their response under abiotic stresses in Camellia sinensis (L.) O. Kuntze

Four typical ALTERNATIVE OXIDASE genes have been identified in tea plants, and their sequence features and gene expression profiles have provided useful information for further studies on function and regulation. Alternative oxidase (AOX) is a terminal oxidase located in the respiratory electron transport chain. AOX catalyzes the oxidation of quinol and the reduction of oxygen into water. In this study, a genome-wide search and subsequent DNA cloning were performed to identify and characterize AOX genes in tea plant (Camellia sinensis (L.) O. Kuntze cv. Longjing43). Our results showed that tea plant possesses four AOX genes, i.e., CsAOX1a, CsAOX1d, CsAOX2a and CsAOX2b. Gene structure and protein sequence analyses revealed that all CsAOXs share a four-exon/three-intron structure with highly conserved regions and amino acid residues, which are necessary for AOX secondary structures, catalytic activities and post-translational regulations. All CsAOX were shown to localize in mitochondria using the green fluorescent protein (GFP)-targeting assay. Both CsAOX1a and CsAOX1d were induced by cold, salt and drought stresses, and with different expression patterns in young and mature leaves. Reactive oxygen species (ROS) accumulated strongly after 72 and 96 h cold treatments in both young and mature leaves, while the polyphenol and total catechin decreased significantly only in mature leaves. In comparison to AtAOX1a in Arabidopsis thaliana, CsAOX1a lost almost all of the stress-responsive cis-acting regulatory elements in its promoter region (1500 bp upstream), but possesses a flavonoid biosynthesis-related MBSII cis-acting regulatory element. These results suggest a link between CsAOX1a function and the metabolism of some secondary metabolites in tea plant. Our studies provide a basis for the further elucidation of the biological function and regulation of the AOX pathway in tea plants.

Identification of the Genomic Region Underlying Seed Weight per Plant in Soybean (Glycine max L. Merr.) via High-Throughput Single-Nucleotide Polymorphisms and a Genome-Wide Association Study

Seed weight per plant (SWPP) of soybean (Glycine max (L.) Merr.), a complicated quantitative trait controlled by multiple genes, was positively associated with soybean seed yields. In the present study, a natural soybean population containing 185 diverse accessions primarily from China was used to analyze the genetic basis of SWPP via genome-wide association analysis (GWAS) based on high-throughput single-nucleotide polymorphisms (SNPs) generated by the Specific Locus Amplified Fragment Sequencing (SLAF-seq) method. A total of 33,149 SNPs were finally identified with minor allele frequencies (MAF) > 5% which were present in 97% of all the genotypes. Twenty association signals associated with SWPP were detected via GWAS. Among these signals, eight SNPs were novel loci, and the other twelve SNPs were overlapped or located in the linked genomic regions of the reported QTL from SoyBase database. Several genes belonging to the categories of hormone pathways, RNA regulation of transcription in plant development, ubiquitin, transporting systems, and other metabolisms were considered as candidate genes associated with SWPP. Furthermore, nine genes from the flanking region of Gm07:19488264, Gm08:15768591, Gm08:15768603, or Gm18:23052511 were significantly associated with SWPP and were stable among multiple environments. Nine out of 18 haplotypes from nine genes showed the effect of increasing SWPP. The identified loci along with the beneficial alleles and candidate genes could be of great value for studying the molecular mechanisms underlying SWPP and for improving the potential seed yield of soybean in the future.

Genome-wide identification and analysis of the ALTERNATIVE OXIDASE gene family in diploid and hexaploid wheat

A comprehensive understanding of wheat responses to environmental stress will contribute to the long-term goal of feeding the planet. ALERNATIVE OXIDASE (AOX) genes encode proteins involved in a bypass of the electron transport chain and are also known to be involved in stress tolerance in multiple species. Here, we report the identification and characterization of the AOX gene family in diploid and hexaploid wheat. Four genes each were found in the diploid ancestors Triticum urartu, and Aegilops tauschii, and three in Aegilops speltoides. In hexaploid wheat (Triticum aestivum), 20 genes were identified, some with multiple splice variants, corresponding to a total of 24 proteins for those with observed transcription and translation. These proteins were classified as AOX1a, AOX1c, AOX1e or AOX1d via phylogenetic analysis. Proteins lacking most or all signature AOX motifs were assigned to putative regulatory roles. Analysis of protein-targeting sequences suggests mixed localization to the mitochondria and other organelles. In comparison to the most studied AOX from Trypanosoma brucei, there were amino acid substitutions at critical functional domains indicating possible role divergence in wheat or grasses in general. In hexaploid wheat, AOX genes were expressed at specific developmental stages as well as in response to both biotic and abiotic stresses such as fungal pathogens, heat and drought. These AOX expression patterns suggest a highly regulated and diverse transcription and expression system. The insights gained provide a framework for the continued and expanded study of AOX genes in wheat for stress tolerance through breeding new varieties, as well as resistance to AOX-targeted herbicides, all of which can ultimately be used synergistically to improve crop yield.

AOX1-Subfamily Gene Members in Olea europaea cv. "Galega Vulgar"-Gene Characterization and Expression of Transcripts during IBA-Induced in Vitro Adventitious Rooting

Propagation of some Olea europaea L. cultivars is strongly limited due to recalcitrant behavior in adventitious root formation by semi-hardwood cuttings. One example is the cultivar ”Galega vulgar”. The formation of adventitious roots is considered a morphological response to stress. Alternative oxidase (AOX) is the terminal oxidase of the alternative pathway of the plant mitochondrial electron transport chain. This enzyme is well known to be induced in response to several biotic and abiotic stress situations. This work aimed to characterize the alternative oxidase 1 (AOX1)-subfamily in olive and to analyze the expression of transcripts during the indole-3-butyric acid (IBA)-induced in vitro adventitious rooting (AR) process. OeAOX1a (acc. no. MF410318) and OeAOX1d (acc. no. MF410319) were identified, as well as different transcript variants for both genes which resulted from alternative polyadenylation events. A correlation between transcript accumulation of both OeAOX1a and OeAOX1d transcripts and the three distinct phases (induction, initiation, and expression) of the AR process in olive was observed. Olive AOX1 genes seem to be associated with the induction and development of adventitious roots in IBA-treated explants. A better understanding of the molecular mechanisms underlying the stimulus needed for the induction of adventitious roots may help to develop more targeted and effective rooting induction protocols in order to improve the rooting ability of difficult-to-root cultivars.

Variation in relative water content, proline accumulation and stress gene expression in two cowpea landraces under drought

Many landraces of cowpea [Vigna unguiculata (L.) Walp.] are adapted to particular geographical and climatic conditions. Here we describe two landraces grown respectively in arid and temperate areas of Algeria and assess their physiological and molecular responses to drought stress. As expected, when deprived of water cowpea plants lose water over time with a gradual reduction in transpiration rate. The landraces differed in their relative water content (RWC) and whole plant transpiration rate. The landrace from Menia, an arid area, retained more water in adult leaves. Both landraces responded to drought stress at the molecular level by increasing expression of stress-related genes in aerial parts, including proline metabolism genes. Expression of gene(s) encoding proline synthesis enzyme P5CS was up regulated and gene expression of ProDH, a proline catabolism enzyme, was down regulated. Relatively low amounts of proline accumulated in adult leaves with slight differences between the two landraces. During drought stress the most apical part of plants stayed relatively turgid with a high RWC compared to distal parts that wilted. Expression of key stress genes was higher and more proline accumulated at the apex than in distal leaves indicating that cowpea has a non-uniform stress response at the whole plant level. Our study reveals a developmental control of water stress through preferential proline accumulation in the upper tier of the cowpea plant. We also conclude that cowpea landraces display physiological adaptations to water stress suited to the arid and temperate climates in which they are cultivated.

A novel and stress adaptive alternative oxidase derived from alternative splicing of duplicated exon in oyster Crassostrea virginica

Alternative oxidase (AOX) is a mitochondrial inner-membrane oxidase that accepts electrons directly from ubiquinol and reduces oxygen to water without involving cytochrome-linked electron transport chain. It is highly conserved in many non-vertebrate taxa and may protect cells against hypoxia and oxidative stress. We identified two AOX mRNAs in eastern oyster Crassostrea virginica, CvAOXA and CvAOXB, which differ by 170 bp but encode AOXs of the same size. Sequence analyses indicate that CvAOX has 10 exons with a tandem duplication of exon 10, and 3' alternative splicing using either the first or second exon 10 produces the two variants CvAOXB or CvAOXA, respectively. The second exon 10 in CvAOXA is more conserved across taxa, while the first exon 10 in CvAOXB contains novel mutations surrounding key functional sites. Both variants are expressed in all organs with the expression of CvAOXA higher than that of CvAOXB under normal condition. Under stress by air exposure, CvAOXB showed significantly higher expression than CvAOXA and became the dominant variant. This is the first case of alternative splicing of duplicated exon in a mollusc that produces a novel variant adaptive to stress, highlighting genome's versatility in generating diversity and phenotypic plasticity.

In silico identification of alternative oxidase 2 (AOX2) in monocots: A new evolutionary scenario

We identified AOX2 genes in monocot species from Lemnoideae (Spirodela polyrhiza, Lemna gibba and Landoltia punctata), Pothoideae (Anthurium andraeanum and Anthurium amnicola) and Monsteroideae (Epipremnum aureum) subfamilies within the Araceae, an early-diverging monocot family. These findings highlight the presence of AOX2 in the most ancient monocot ancestor and also that at least partial loss of this gene occurred during speciation events within several monocot orders. The presence of AOX2 in monocot species challenges (1) new understanding of the evolutionary history of the AOX gene family in angiosperms and (2) drives experimental and bioinformatics efforts to explore functional relevance of the two AOX gene family members for plant growth and development. Knowledge gain in this field will impact running strategies on AOX-derived functional marker candidate development for plant breeding.

Wild Carrot Differentiation in Europe and Selection at DcAOX1 Gene?

By definition, the domestication process leads to an overall reduction of crop genetic diversity. This lead to the current search of genomic regions in wild crop relatives (CWR), an important task for modern carrot breeding. Nowadays massive sequencing possibilities can allow for discovery of novel genetic resources in wild populations, but this quest could be aided by the use of a surrogate gene (to first identify and prioritize novel wild populations for increased sequencing effort). Alternative oxidase (AOX) gene family seems to be linked to all kinds of abiotic and biotic stress reactions in various organisms and thus have the potential to be used in the identification of CWR hotspots of environment-adapted diversity. High variability of DcAOX1 was found in populations of wild carrot sampled across a West-European environmental gradient. Even though no direct relation was found with the analyzed climatic conditions or with physical distance, population differentiation exists and results mainly from the polymorphisms associated with DcAOX1 exon 1 and intron 1. The relatively high number of amino acid changes and the identification of several unusually variable positions (through a likelihood ratio test), suggests that DcAOX1 gene might be under positive selection. However, if positive selection is considered, it only acts on some specific populations (i.e. is in the form of adaptive differences in different population locations) given the observed high genetic diversity. We were able to identify two populations with higher levels of differentiation which are promising as hot spots of specific functional diversity.

Phylogenetic analysis and differential expression of EF1α genes in soybean during development, stress and phytohormone treatments

The EF1α is a multifunctional protein with additional unrelated activities to its primary function in translation. This protein is encoded by a multigene family and few studies are still available in plants. Expression of six EF1α genes in Glycine max was performed using RT-qPCR and RNA-seq data to advance in the function of each gene during plant development, stress conditions and phytohormone treatments. A phylogenetic classification in Phaseoleae tribe was used to identify the G. max EF1α genes (EF1α 1a1, 1a2, 1b, 2a, 2b and 3). Three EF1α types (1-3) were found in Phaseoleae revealing duplications in G. max types 1 and 2. EF1α genes were expressed in all studied tissues, however, specific amount of each transcript was detected. In plant development, all EF1α transcripts were generally more expressed in younger tissues, however, in unifoliolate leaves and cotyledons a higher expression occurred in older tissues. Five EF1α genes (except 2a) were up-regulated under stress in a response tissue/stress/cultivar-dependent. EF1α 3 was the most stress-induced gene linked to cultivar stress tolerance mainly in aerial tissues. Auxin, salicylate and ethylene induced differentially the EF1α expression. Overall, this study provides a consistent EF1α classification in Phaseoleae tribe to better understand their functional evolution. The RT-qPCR and RNA-seq EF1α expression profiles were consistent, both exhibiting expression diversification of each gene (spatio-temporal, stress and phytohormone stimuli). Our results point out the EF1α genes, especially EF1α 3, as candidate for developing a useful tool for future G. max breeding.

Misannotation Awareness: A Tale of Two Gene-Groups

Incorrectly or simply not annotated data is largely increasing in most public databases, undoubtedly caused by the rise in sequence data and the more recent boom of genomic projects. Molecular biologists and bioinformaticists should join efforts to tackle this issue. Practical challenges have been experienced when studying the alternative oxidase (AOX) gene family, and hence the motivation for the present work. Commonly used databases were screened for their capacity to distinguish AOX from the plastid terminal oxidase (also called plastoquinol terminal oxidase; PTOX) and we put forward a simple approach, based on amino acids signatures, that unequivocally distinguishes these gene families. Further, available sequence data on the AOX family in plants was carefully revised to: (1) confirm the classification as AOX and (2) identify to which AOX family member they belong to. We bring forward the urgent need of misannotation awareness and re-annotation of public AOX sequences by highlighting different types of misclassifications and the large under-estimation of data availability.

Alternative oxidase pathway is involved in the exogenous SNP-elevated tolerance of Medicago truncatula to salt stress

Exogenous application of sodium nitroprusside (SNP) would enhance the tolerance of plants to stress conditions. Some evidences suggested that nitric oxide (NO) could induce the expression of alternative oxidase (AOX). In this study, Medicago truncatula (Medicago) was chosen to study the role of AOX in the SNP-elevated resistance to salt stress. Our results showed that the expression of AOX genes (especially AOX1 and AOX2b1) and cyanide-resistant respiration rate (Valt) could be significantly induced by salt stress. Exogenous application of SNP could further enhance the expression of AOX genes and Valt. Exogenous application of SNP could alleviate the oxidative damage and photosynthetic damage caused by salt stress. However, the stress resistance was significantly decreased in the plants which were pretreated with n-propyl gallate (nPG). More importantly, the damage in nPG-pretreated plants could not be alleviated by application of SNP. Further study showed that effects of nPG on the activities of antioxidant enzymes were minor. These results showed that AOX pathway played an important role in the SNP-elevated resistance of Medicago to salt stress. AOX could contribute to regulating the accumulation of reactive oxygen (ROS) and protect of photosystem, and we proposed that all these were depend on the ability of maintaining the homeostasis of redox state.

Stress-Induced Accumulation of DcAOX1 and DcAOX2a Transcripts Coincides with Critical Time Point for Structural Biomass Prediction in Carrot Primary Cultures (Daucus carota L.)

Stress-adaptive cell plasticity in target tissues and cells for plant biomass growth is important for yield stability. In vitro systems with reproducible cell plasticity can help to identify relevant metabolic and molecular events during early cell reprogramming. In carrot, regulation of the central root meristem is a critical target for yield-determining secondary growth. Calorespirometry, a tool previously identified as promising for predictive growth phenotyping has been applied to measure the respiration rate in carrot meristem. In a carrot primary culture system (PCS), this tool allowed identifying an early peak related with structural biomass formation during lag phase of growth, around the 4th day of culture. In the present study, we report a dynamic and correlated expression of carrot AOX genes (DcAOX1 and DcAOX2a) during PCS lag phase and during exponential growth. Both genes showed an increase in transcript levels until 36 h after explant inoculation, and a subsequent down-regulation, before the initiation of exponential growth. In PCS growing at two different temperatures (21°C and 28°C), DcAOX1 was also found to be more expressed in the highest temperature. DcAOX genes' were further explored in a plant pot experiment in response to chilling, which confirmed the early AOX transcript increase prior to the induction of a specific anti-freezing gene. Our findings point to DcAOX1 and DcAOX2a as being reasonable candidates for functional marker development related to early cell reprogramming. While the genomic sequence of DcAOX2a was previously described, we characterize here the complete genomic sequence of DcAOX1.

Alternative Oxidase Gene Family in Hypericum perforatum L.: Characterization and Expression at the Post-germinative Phase

Alternative oxidase (AOX) protein is located in the inner mitochondrial membrane and is encoded in the nuclear genome being involved in plant response upon a diversity of environmental stresses and also in normal plant growth and development. Here we report the characterization of the AOX gene family of Hypericum perforatum L. Two AOX genes were identified, both with a structure of four exons (HpAOX1, acc. KU674355 and HpAOX2, acc. KU674356). High variability was found at the N-terminal region of the protein coincident with the high variability identified at the mitochondrial transit peptide. In silico analysis of regulatory elements located at intronic regions identified putative sequences coding for miRNA precursors and trace elements of a transposon. Simple sequence repeats were also identified. Additionally, the mRNA levels for the HpAOX1 and HpAOX2, along with the ones for the HpGAPA (glyceraldehyde-3-phosphate dehydrogenase A subunit) and the HpCAT1 (catalase 1), were evaluated during the post-germinative development. Gene expression analysis was performed by RT-qPCR with accurate data normalization, pointing out HpHYP1 (chamba phenolic oxidative coupling protein 1) and HpH2A (histone 2A) as the most suitable reference genes (RGs) according to GeNorm algorithm. The HpAOX2 transcript demonstrated larger stability during the process with a slight down-regulation in its expression. Contrarily, HpAOX1 and HpGAPA (the corresponding protein is homolog to the chloroplast isoform involved in the photosynthetic carbon assimilation in other plant species) transcripts showed a marked increase, with a similar expression pattern between them, during the post-germinative development. On the other hand, the HpCAT1 (the corresponding protein is homolog to the major H2O2-scavenging enzyme in other plant species) transcripts showed an opposite behavior with a down-regulation during the process. In summary, our findings, although preliminary, highlight the importance to investigate in more detail the participation of AOX genes during the post-germinative development in H. perforatum, in order to explore their functional role in optimizing photosynthesis and in the control of reactive oxygen species (ROS) levels during the process.

Physiological role of alternative oxidase (from yeasts to plants)

Mitochondria of all so far studied organisms, with the exception of Archaea, mammals, some yeasts, and protists, contain, along with the classical phosphorylating cytochrome pathway, a so-called cyanide-insensitive alternative oxidase (AOX) localized on the matrix side of the mitochondrial inner membrane, and electron transport through which is not coupled with ATP synthesis and energy accumulation. Mechanisms underlying plentiful functions of AOX in organisms at various levels of organization ranging from yeasts to plants are considered. First and foremost, AOX provides a chance of cell survival after inhibiting the terminal components of the main respiratory chain or losing the ability to synthesize these components. The vitally important role of AOX is obvious in thermogenesis of thermogenic plant organs where it becomes the only terminal oxidase with a very high activity, and the energy of substrate oxidation by this respiratory pathway is converted into heat, thus promoting evaporation of volatile substances attracting pollinating insects. AOX plays a fundamentally significant role in alleviating or preventing oxidative stress, thus ensuring the defense against a wide range of stresses and adverse environmental conditions, such as changes in temperature and light intensities, osmotic stress, drought, and attack by incompatible strains of bacterial pathogens, phytopathogens, or their elicitors. Participation of AOX in pathogen survival during its existence inside the host, in antivirus defense, as well as in metabolic rearrangements in plants during embryogenesis and cell differentiation is described. Examples are given to demonstrate that AOX might be an important tool to overcome the adverse aftereffects of restricted activity of the main respiratory chain in cells and whole animals.

Nitric oxide mediated amelioration of arsenic toxicity which alters the alternative oxidase (Aox1) gene expression in Hordeum vulgare L

The role of nitric oxide (NO) as a key molecule in the signal transduction pathway of a biotic stress response has already been described. Recent studies indicate that it also participate in the signaling of abiotic stresses. In the present study, we showed the altered expression of stress responsive gene alternative oxidase (Aox1) in seedlings of barley (Hordeum vulgare L.) in response to arsenic toxicity. Arsenic toxicity decreased the germination percentage, biomass, chlorophyll and carotenoid content whereas, arsenic toxicity enhanced the MDA content and proline content in a dose dependent manner. Other enzyme activities like catalase and superoxide dismutase increased with the increase in concentrations but it fell down at higher concentration of arsenic. Pretreatment of nitric oxide results in the enhanced expression of alternative oxidase which showed the adaptation of alternative pathway during the arsenic stress and it also enhances the growth ability and adaptability towards the arsenic stress. The results support the conclusion that nitric oxide ameliorates the arsenic toxicity not only at the level of antioxidant defense but also by affecting other mechanism of detoxification.

Alternative oxidase: distribution, induction, properties, structure, regulation, and functions

The respiratory chain in the majority of organisms with aerobic type metabolism features the concomitant existence of the phosphorylating cytochrome pathway and the cyanide- and antimycin A-insensitive oxidative route comprising a so-called alternative oxidase (AOX) as a terminal oxidase. In this review, the history of AOX discovery is described. Considerable evidence is presented that AOX occurs widely in organisms at various levels of organization and is not confined to the plant kingdom. This enzyme has not been found only in Archaea, mammals, some yeasts and protists. Bioinformatics research revealed the sequences characteristic of AOX in representatives of various taxonomic groups. Based on multiple alignments of these sequences, a phylogenetic tree was constructed to infer their possible evolution. The ways of AOX activation, as well as regulatory interactions between AOX and the main respiratory chain are described. Data are summarized concerning the properties of AOX and the AOX-encoding genes whose expression is either constitutive or induced by various factors. Information is presented on the structure of AOX, its active center, and the ubiquinone-binding site. The principal functions of AOX are analyzed, including the cases of cell survival, optimization of respiratory metabolism, protection against excess of reactive oxygen species, and adaptation to variable nutrition sources and to biotic and abiotic stress factors. It is emphasized that different AOX functions complement each other in many instances and are not mutually exclusive. Examples are given to demonstrate that AOX is an important tool to overcome the adverse aftereffects of restricted activity of the main respiratory chain in cells and whole animals. This is the first comprehensive review on alternative oxidases of various organisms ranging from yeasts and protists to vascular plants.

Cucumber Possesses a Single Terminal Alternative Oxidase Gene That is Upregulated by Cold Stress and in the Mosaic (MSC) Mitochondrial Mutants

Alternative oxidase (AOX) is a mitochondrial terminal oxidase which is responsible for an alternative route of electron transport in the respiratory chain. This nuclear-encoded enzyme is involved in a major path of survival under adverse conditions by transfer of electrons from ubiquinol instead of the main cytochrome pathway. AOX protects against unexpected inhibition of the cytochrome c oxidase pathway and plays an important role in stress tolerance. Two AOX subfamilies (AOX1 and AOX2) exist in higher plants and are usually encoded by small gene families. In this study, genome-wide searches and cloning were completed to identify and characterize AOX genes in cucumber (Cucumis sativus L.). Our results revealed that cucumber possesses no AOX1 gene(s) and only a single AOX2 gene located on chromosome 4. Expression studies showed that AOX2 in wild-type cucumber is constitutively expressed at low levels and is upregulated by cold stress. AOX2 transcripts and protein were detected in leaves and flowers of wild-type plants, with higher levels in the three independently derived mosaic (MSC) mitochondrial mutants. Because cucumber possesses a single AOX gene and its expression increases under cold stress and in the MSC mutants, this plant is a unique and intriguing model to study AOX expression and regulation particularly in the context of mitochondria-to-nucleus retrograde signaling.

Evolution and association analysis of GmCYP78A10 gene with seed size/weight and pod number in soybean

Seed-size/weight traits, controlled by multiple genes in soybean, play an important role in determining seed yield. However, the molecular mechanisms controlling the seed size and weight in soybean remain unclear. In Arabidopsis, P450/CYP78A gene family has been proved extremely relevant to seed size (such as AtCYP78A5, AtCYP78A6 and AtCYP78A9). We found that a soybean GmCYP78A10 gene underwent artificial selection during soybean breeding. The GmCYP78A10a allele mainly distributed in wild soybean (Glycine soja), but has been eliminated in the cultivars during early stage of soybean breeding, while the GmCYP78A10b allele has been accumulated and become the predominant allele in cultivated soybean (G. max). ANOVA analysis showed that the mean seed weight, seed width and seed thickness of soybean varieties with GmCYP78A10b allele was significantly heavier/bigger than those with GmCYP78A10a allele (P < 0.01). The allele could explain 7.2 % variation in seed weight. The pod number of the soybeans with GmCYP78A10b allele significantly decreased compared to those with GmCYP78A10a allele (P < 0.01, R(2) = 5.8 %), while other agronomic traits including seed weight/plant were not significantly affected by these two alleles. We speculated that during the early stage of soybean breeding, breeders selected big seed carrying GmCYP78A10b allele, but lowered pod number simultaneously. Overall, the selection did not cause the significantly change in soybean seed yield. Our results suggests that the soybean GmCYP78A10 gene may have a similar function to those genes belonging to P450/CYP78A subfamily in Arabidopsis and provides new information for the genetic control of seed size in soybean.

Selection of suitable soybean EF1α genes as internal controls for real-time PCR analyses of tissues during plant development and under stress conditions

KEY MESSAGE

The EF1α genes were stable in the large majority of soybean tissues during development and in specific tissues/conditions under stress. Quantitative real-time PCR (qPCR) analysis strongly depends on transcript normalization using stable reference genes. Reference genes are generally encoded by multigene families and are used in qPCR normalization; however, little effort has been made to verify the stability of different gene members within a family. Here, the expression stability of members of the soybean EF1α gene family (named EF1α 1a1, 1a2, 1b, 2a, 2b and 3) was evaluated in different tissues during plant development and stress exposure (SA and PEG). Four genes (UKN1, SKIP 16, EF1β and MTP) already established as stably expressed were also used in the comparative analysis. GeNorm analyses revealed different combinations of reference genes as stable in soybean tissues during development. The EF1α genes were the most stable in cotyledons (EF1α 3 and EF1α 1b), epicotyls (EF1α 1a2, EF1α 2b and EF1α 1a1), hypocotyls (EF1α 1a1 and EF1β), pods (EF1α 2a and EF1α 2b) and roots (EF1α 2a and UKN1) and less stable in tissues such as trifoliate and unifoliate leaves and germinating seeds. Under stress conditions, no suitable combination including only EF1α genes was found; however, some genes were relatively stable in leaves (EF1α 1a2) and roots (EF1α 1a1) treated with SA as well as in roots treated with PEG (EF1α 2b). EF1α 2a was the most stably expressed EF1α gene in all soybean tissues under stress. Taken together, our data provide guidelines for the selection of EF1α genes for use as reference genes in qPCR expression analyses during plant development and under stress conditions.

Alternative oxidase inhibitors as antiparasitic agents against scuticociliatosis

Philasterides dicentrarchi causes a severe disease in turbot, and at present there are no drugs available to treat infected fish. We have previously demonstrated that, in addition to the classical respiratory pathway, P. dicentrarchi possesses an alternative mitochondrial respiratory pathway that is cyanide-insensitive and salicylhydroxamic acid (SHAM)-sensitive. In this study, we found that during the initial phase of growth in normoxia, ciliate respiration is sensitive to the natural polyphenol resveratrol (RESV) and to Antimycin A (AMA). However, under hypoxic conditions, the parasite utilizes AMA-insensitive respiration, which is completely inhibited by RESV and by the antioxidant propyl gallate (PG), an alternative oxidase (AOX) inhibitor. PG caused significantly dose-dependent inhibition of the in vitro growth of the parasite under normoxia and hypoxia and an over-expression of heat shock proteins of the Hsp70 subfamily. RESV and PG may affect the protective role of the AOX against mitochondrial oxidative stress, leading to an impaired mitochondrial membrane potential and mitochondrial dysfunction, which the parasite attempts to neutralize by increasing the expression of Hsp70. In view of the antiparasitic effects induced by AOX inhibitors and the absence of AOX in their host, this enzyme constitutes a potential target for the development of new drugs against scuticociliatosis.

Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant infer that fiber cell wall development is associated with stress responses

BACKGROUND

Cotton fiber maturity is an important factor for determining the commercial value of cotton. How fiber cell wall development affects fiber maturity is not well understood. A comparison of fiber cross-sections showed that an immature fiber (im) mutant had lower fiber maturity than its near isogenic wild type, Texas marker-1 (TM-1). The availability of the im mutant and TM-1 provides a unique way to determine molecular mechanisms regulating cotton fiber maturity.

RESULTS

Transcriptome analysis showed that the differentially expressed genes (DEGs) in the im mutant fibers grown under normal stress conditions were similar to those in wild type cotton fibers grown under severe stress conditions. The majority of these DEGs in the im mutant were related to stress responses and cellular respiration. Stress is known to reduce the activity of a classical respiration pathway responsible for energy production and reactive oxygen species (ROS) accumulation. Both energy productions and ROS levels in the im mutant fibers are expected to be reduced if the im mutant is associated with stress responses. In accord with the prediction, the transcriptome profiles of the im mutant showed the same alteration of transcriptional regulation that happened in energy deprived plants in which expressions of genes associated with cell growth processes were reduced whereas expressions of genes associated with recycling and transporting processes were elevated. We confirmed that ROS production in developing fibers from the im mutant was lower than that from the wild type. The lower production of ROS in the im mutant fibers might result from the elevated levels of alternative respiration induced by stress.

CONCLUSION

The low degree of fiber cell wall thickness of the im mutant fibers is associated with deregulation of the genes involved in stress responses and cellular respiration. The reduction of ROS levels and up-regulation of the genes involved in alternative respirations suggest that energy deprivation may occur in the im mutant fibers.

Identification of duplicated and stress-inducible Aox2b gene co-expressed with Aox1 in species of the Medicago genus reveals a regulation linked to gene rearrangement in leguminous genomes

In flowering plants, alternative oxidase (Aox) is encoded by 3-5 genes distributed in 2 subfamilies (Aox1 and Aox2). In several species only Aox1 is reported as a stress-responsive gene, but in the leguminous Vigna unguiculata Aox2b is also induced by stress. In this work we investigated the Aox genes from two leguminous species of the Medicago genus (Medicago sativa and Medicago truncatula) which present one Aox1, one Aox2a and an Aox2b duplication (named here Aox2b1 and Aox2b2). Expression analyses by semi-quantitative RT-PCR in M. sativa revealed that Aox1, Aox2b1 and Aox2b2 transcripts increased during seed germination. Similar analyses in leaves and roots under different treatments (SA, PEG, H2O2 and cysteine) revealed that these genes are also induced by stress, but with peculiar spatio-temporal differences. Aox1 and Aox2b1 showed basal levels of expression under control conditions and were induced by stress in leaves and roots. Aox2b2 presented a dual behavior, i.e., it was expressed only under stress conditions in leaves, and showed basal expression levels in roots that were induced by stress. Moreover, Aox2a was expressed at higher levels in leaves and during seed germination than in roots and appeared to be not responsive to stress. The Aox expression profiles obtained from a M. truncatula microarray dataset also revealed a stress-induced co-expression of Aox1, Aox2b1 and Aox2b2 in leaves and roots. These results reinforce the stress-inducible co-expression of Aox1/Aox2b in some leguminous plants. Comparative genomic analysis indicates that this regulation is linked to Aox1/Aox2b proximity in the genome as a result of the gene rearrangement that occurred in some leguminous plants during evolution. The differential expression of Aox2b1/2b2 suggests that a second gene has been originated by recent gene duplication with neofunctionalization.

Expression and signal regulation of the alternative oxidase genes under abiotic stresses

Plants in their natural environment frequently face various abiotic stresses, such as drought, high salinity, and chilling. Plant mitochondria contain an alternative oxidase (AOX), which is encoded by a small family of nuclear genes. AOX genes have been shown to be highly responsive to abiotic stresses. Using transgenic plants with varying levels of AOX expression, it has been confirmed that AOX genes are important for abiotic stress tolerance. Although the roles of AOX under abiotic stresses have been extensively studied and there are several excellent reviews on this topic, the differential expression patterns of the AOX gene family members and the signal regulation of AOX gene(s) under abiotic stresses have not been extensively summarized. Here, we review and discuss the current progress of these two important issues.

Unravelling mitochondrial retrograde regulation in the abiotic stress induction of rice ALTERNATIVE OXIDASE 1 genes

Mitochondrial retrograde regulation (MRR) is the transduction of mitochondrial signals to mediate nuclear gene expression. It is not clear whether MRR is a common regulation mechanism in plant abiotic stress response. In this study, we analysed the early abiotic stress response of the rice OsAOX1 genes, and the induction of OsAOX1a and OsAOX1b (OsAOX1a/b) was selected as a working model for the stress-induced MRR studies. We found that the induction mediated by the superoxide ion (O2·(-) )-generating chemical methyl viologen was stronger than that of hydrogen peroxide (H2 O2 ). The addition of reactive oxygen species (ROS) scavengers demonstrated that the stress induction was reduced by eliminating O2·(-) . Furthermore, the stress induction did not rely on chloroplast- or cytosol-derived O2·(-) . Next, we generated transgenic plants overexpressing the superoxide dismutase (SOD) gene at different subcellular locations. The results suggest that only the mitochondrial SOD, OsMSD, attenuated the stress induction of OsAOX1a/b specifically. Therefore, our findings demonstrate that abiotic stress initiates the MRR on OsAOX1a/b and that mitochondrial O2·(-) is involved in the process.

Catalase plays a key role in salt stress acclimation induced by hydrogen peroxide pretreatment in maize

Pretreatment in plants is recognized as a valuable strategy to stimulate plant defenses, leading to better plant development. This study evaluated the effects of H₂O₂ leaf spraying pretreatment on plant growth and investigated the antioxidative mechanisms involved in the response of maize plants to salt stress. It was found that salinity reduced maize seedling growth when compared to control conditions, and H₂O₂ foliar spraying was effective in minimizing this effect. Analysis of the antioxidative enzymes catalase (EC 1.11.1.6), guaiacol peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.1) and superoxide dismutase (EC 1.15.1.1) revealed that H₂O₂ spraying increased antioxidant enzyme activities. Catalase (CAT) was the most responsive of these enzymes to H₂O₂, with higher activity early (48 h) in the treatment, while guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) were responsive only at later stages (240 h) of treatment. Increased CAT activity appears linked to gene expression regulation. Lower malondialdehyde levels were detected in plants with higher CAT activity, which may result from the protective function of this enzyme. Overall, we can conclude that pretreatment with H₂O₂ leaf spraying was able to reduce the deleterious effects of salinity on seedling growth and lipid peroxidation. These responses could be attributed to the ability of H₂O₂ to induce antioxidant defenses, especially CAT activity.

Alternative oxidase (AOX) and phenolic metabolism in methyl jasmonate-treated hairy root cultures of Daucus carota L

Methyl-jasmonate (MJ)-treated hairy roots of Daucus carota L. were used to study the influence of alternative oxidase (AOX) in phenylpropanoid metabolism. Phenolic acid accumulation, as well as total flavonoids and lignin content of the MJ-treated hairy roots were decreased by treatment with salicylhydroxamic acid (SHAM), a known inhibitor of AOX. The inhibitory effect of SHAM was concentration dependent. Treatment with propyl gallate (PG), another inhibitor of AOX, also had a similar inhibitory effect on accumulation of phenolic acid, total flavonoids and lignin. The transcript levels of two DcAOX genes (DcAOX2a and DcAOX1a) were monitored at selected post-elicitation time points. A notable rise in the transcript levels of both DcAOX genes was observed preceding the MJ-induced enhanced accumulation of phenolics, flavonoids and lignin. An appreciable increase in phenylalanine ammonia-lyase (PAL) transcript level was also observed prior to enhanced phenolics accumulation. Both DcAOX genes showed differential transcript accumulation patterns after the onset of elicitation. The transcript levels of DcAOX1a and DcAOX2a attained peak at 6hours post elicitation (hpe) and 12hpe, respectively. An increase in the transcript levels of both DcAOX genes preceding the accumulation of phenylpropanoid-derivatives and lignin showed a positive correlation between AOX activity and phenylpropanoid biosynthesis. The results provide important new insight about the influence of AOX in phenylpropanoid biosynthesis.

Modified expression of alternative oxidase in transgenic tomato and petunia affects the level of tomato spotted wilt virus resistance

BACKGROUND

Tomato spotted wilt virus (TSWV) has a very wide host range, and is transmitted in a persistent manner by several species of thrips. These characteristics make this virus difficult to control. We show here that the over-expression of the mitochondrial alternative oxidase (AOX) in tomato and petunia is related to TSWV resistance.

RESULTS

The open reading frame and full-length sequence of the tomato AOX gene LeAox1au were cloned and introduced into tomato 'Healani' and petunia 'Sheer Madness' using Agrobacterium-mediated transformation. Highly expressed AOX transgenic tomato and petunia plants were selfed and transgenic R1 seedlings from 10 tomato lines and 12 petunia lines were used for bioassay. For each assayed line, 22 to 32 tomato R1 progeny in three replications and 39 to 128 petunia progeny in 13 replications were challenged with TSWV. Enzyme-Linked Immunosorbent Assays showed that the TSWV levels in transgenic tomato line FKT4-1 was significantly lower than that of wild-type controls after challenge with TSWV. In addition, transgenic petunia line FKP10 showed significantly less lesion number and smaller lesion size than non-transgenic controls after inoculation by TSWV.

CONCLUSION

In all assayed transgenic tomato lines, a higher percentage of transgenic progeny had lower TSWV levels than non-transgenic plants after challenge with TSWV, and the significantly increased resistant levels of tomato and petunia lines identified in this study indicate that altered expression levels of AOX in tomato and petunia can affect the levels of TSWV resistance.