Search

The purpose of this study was to determine the agro-morphological, physiological, and transcriptional characteristics of ethyl methane sulfonate (EMS)-mutagenized M3 alfalfa (Medicago sativa L.) mutants grown for 24 days under water deficit conditions following the first cutting at the blooming bud stage. Drought stress generally reduced all agro-morphological parameters measured. Cutting stress significantly reduced total chlorophyll contents of all genotypes, with the exception of mutant X20. Significant changes occurred in the levels of ascorbate peroxidase (APX), lipid peroxidation (TBARS), glutathione reductase (GR), superoxide dismutase (SOD) and crude protein levels. Drought stress considerably elevated GR levels in irrigated control (C1) and unirrigated control (C2) plants. In contrast to the other genotypes studied, mutant X20's crude protein level increased significantly after the first cutting under 24 days of water deficit conditions, compared to the level found before cutting. The expression profiles of Medicago truncatula Response to Desiccation 2 (MtRD2) and Medicago sativa proline dehydrogenase (MsProDH) genes differed based on the plant genotype and duration of drought stress. Drought stress increased MsProDH gene expression in X20, X50, and C2 plants by 4.57, 14.8, and 20.65 times, respectively. The findings of the expression study indicated that the MtRD2 gene may play a key role in stress reduction rather than drought stress per se. The results of this study revealed that cutting and drought are two independent stress variables that should be evaluated separately when evaluating genotype response to both irrigated and unirrigated growing environments in alfalfa. [ABSTRACT FROM AUTHOR]

Plant Na+/H+antiporter (NHX) genes enhance salt tolerance by preventing excessive Na+ accumulation in the cytosol through partitioning of Na+ ions into vacuoles or extracellular transport across the plasma membrane. However, there is limited detailed information regarding the salt stress responsive SlNHXs in the most recent tomato genome. We investigated the role of this gene family's expression patterns in the open flower tissues under salt shock in Solanum lycopersicum using a genome‐wide approach. A total of seven putative SlNHX genes located on chromosomes 1, 4, 6, and 10 were identified, but no ortholog of the NHX5 gene was identified in the tomato genome. Phylogenetic analysis revealed that these genes are divided into three different groups. SlNHX proteins with 10–12 transmembrane domains were hypothetically localized in vacuoles or cell membranes. Promoter analysis revealed that SlNHX6 and SlNHX8 are involved with the stress‐related MeJA hormone in response to salt stress signaling. The structural motif analysis of SlNHX1, −2, −3, −4, and −6 proteins showed that they have highly conserved amiloride binding sites. The protein–protein network revealed that SlNHX7 and SlNHX8 interact physically with Salt Overly Sensitive (SOS) pathway proteins. Transcriptome analysis demonstrated that the SlNHX2 and SlNHX6 genes were substantially expressed in the open flower tissues. Moreover, quantitative PCR analysis indicated that all SlNHX genes, particularly SlNHX6 and SlNHX8, are significantly upregulated by salt shock in the open flower tissues. Our results provide an updated framework for future genetic research and development of breeding strategies against salt stress in the tomato. [ABSTRACT FROM AUTHOR]

This study has been conducted to determine genetic diversity of the common vetch lines and cultivars by using pairwise combinations of universal rice primers (URPs). A total number of 37 URP marker pairs were tested and twenty of those provided amplicons in the common vetch genome. The pairs of amplified URP markers provided a total of 83 bands and 62 of them were determined as polymorphic and were scattered to the whole genome. The average polymorphism rate of the primers was calculated as 73.5% while the polymorphism information content (PIC) values have ranged from 0.11 to 0.47 with an average of 0.24. The phylogenetic tree constructed based on UPGMA analysis provided three main clades. Two-dimensional plot of PCA and the UPGMA analysis showed that the URP markers successfully distinguished the genetic material based on their genetic origin. In conclusion, this study revealed that the use of pairwise combinations of URP markers could have a better power to reveal the level of polymorphism in plant genome. [ABSTRACT FROM AUTHOR]

Background: Einkorn wheat is one of the first primary genetic resources for discovery of new alleles related to biotic and abiotic stress tolerances for further genetic improvements while it became more popular especially for its native grain status as healthy food resources. Therefore, this study aims to determine germination parameters of 32 local einkorn (Triticum monococcum) genotypes collected from Kastamonu and its vicinity, Turkey under drought stress conditions, and to reveal the genetic relationship of those genotypes based on drought related gene targeted functional markers (GTFMs). Methods and results: Germination test was conducted at 20 ± 0.5 °C in darkness with randomized complete block design with 4 replications. Seeds placed on double filter papers in a covered glass petri dishes (80 × 15 mm) were treated with polyethylene glycol (PEG6000) with a -0.23 MPa. The final germination percentages (FGPs), speed and span of germination parameters were determined. Drought stress severely worsened all germination parameters measured. The genotypes SG24 and SG12 were the most drought tolerant and sensitive genotypes based on 21.1% and 64.8% of reduction rates in FGPs, respectively. Twelve GTFMs produced a total of 32 bands and 26 of them were polymorphic. The mean polymorphism ratio of the markers and average band per marker were determined as 86.31% and 2.66, respectively. The highest polymorphism information content (PIC) was obtained from AIB1 gene marker (0.875). Conclusions: This study revealed that there was a significant genetic variation for drought tolerance levels of local einkorn wheat genotypes at germination stage and drought related GTFMs can be used not only to reveal genetic variation but also to distinguish the drought tolerant genotypes. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine drought tolerant novel mutant of alfalfa (Medicago sativa L.) genotypes by screening EMS mutagenized 340675 M3 seeds at germination stages in the presence of osmotic stress of 35% PEG6000. Root growth assay provided several drought tolerant candidate mutants. Of those, 4 mutants were further evaluated at water deficit conditions applied for 24 days after the first cutting at flowering bud stage. The results revealed that mutants determined as drought tolerant at germination stage were also tolerant to water deficit conditions. Protein content and superoxide dismutase values were found to be higher in all mutants than controls. Ascorbate peroxides, glutton reductase and lipid peroxidase values varied based on the mutant genotype and duration of drought stress. Drought stress significantly changed transcriptional levels of MtP5CS, MtDehyd, MseIF-2, MtRD2 and MsNAC genes. These results indicated that in vitro screening of alfalfa mutant seeds for osmatic tolerance at germination and early seedling growth stages was successfully able to determine the drought tolerant alfalfa mutants which were also tolerant to water deficit conditions after the first cutting at flowering bud stage. [ABSTRACT FROM AUTHOR]

The objectives of the present study were to determine salt tolerance levels of 12 different common vetch (Vicia sativa L.) cultivars at germination stage in the presence of 250 mM NaCl and to reveal genetic relationships based on gene targeted functional markers (GTFMs) associated with salt tolerance. The results revealed the presence of a significant genetic variation among the cultivars although salt stress significantly reduced all germination parameters tested. The cultivar Ozveren was the most salt tolerant with 20.1% reduction in final germination percentage compared to control seeds while cultivars Alınoglu, Ayaz and Bakir did not germinate. The maximum delays in germination rate (G50 = 3.78 days) and synchrony (G10-90 = 3.45 days) were obtained from the cultivars Urkmez and Ozveren, respectively. The GTFMs provided a total of 53.1% polymorphism. The primers of MtSOS2 gene gave the highest numbers of alleles per primer pair while the highest polymorphism rate (77.8%) was obtained from the MtP5CS gene. The first three components of principal component analysis explained 57.63% of total variation. This study concluded that the cultivars determined to be salt tolerant and sensitive at germination stage distributed into three main clades determined by UPGMA analysis while the GTFMs associated with salt tolerance successfully determined the genetic relationships of common vetch cultivars. [ABSTRACT FROM AUTHOR]

The aim of this study was to make morphological and molecular characterization of tall wheatgrass (Thinopyrum ponticum) accessions naturally found in Canakkale flora, Turkey. The seeds collected from 24 different locations in Canakkale vicinity were planted in the nursery field to determine thirteen morphological parameters. Twelve universal rice primers (URPs) were used to reveal genetic relationship among the accessions while ploidy analysis was done based on the nuclear DNA content of plants determined by Flow cytometer. Fluorescence in situ hybridization (FISH) method was used to determine 5S and 45S rDNA distributions on mitotic chromosomes. The agro-morphological data showed significant variation among the accessions for all parameters measured, except the number of nodes per plant. Twelve URP primers produced 73 alleles in total and 63 of those were polymorphic. The highest polymorphism information content value was obtained from URP 17R with 0.82. The first three components of Eigen values in PCA analysis explained 41.1% of total variation. The 2C nuclear DNA contents of the accessions ranged from 41.17 to 45.49 pg. All the accessions were determined as decaploid with 2n = 70 chromosomes. FISH analysis provided 18–20 interstial 5S rDNA and 12–14 terminal 45S rDNA loci. The results concluded that tall wheatgrass accessions used in this study contain a significant variation in morphological traits and PCR-based DNA polymorphism which could be used as a new genetic resource in breeding programs of tall wheatgrass and wheat improvement for intra- and intergeneric crosses. [ABSTRACT FROM AUTHOR]

This study was initiated to reveal genetic relationship of 25 tef (Eragrostis tef (Zucc.) accessions by using 10 SSR markers and to determine DNA content variation by using flow cytometer analysis. Ten markers produced a total of 18 alleles and 11 of those were polymorphic. The mean polymorphism rate was 66.6%. The highest polymorphism information content value was obtained from marker CNLTs370 with 0.69 while markers CNTLs11 and CNTLs133 produced monomorphic bands only. UPGMA analysis divided 25 tef genotypes into three main clades. The accessions PI193511 and PI195934 were distinctly separated from the others. No ploidy differences were determined among the 25 tef accessions. 2C mean nuclear DNA content ranged from 1.406 pg to 1.510 with mean of 1.460 pg. The results of this study indicated that SSR markers successfully determined genetic relationship of 25 tef accession although they had a low rate of polymorphism. This study also revealed that available tef related SSR markers should be optimized before use and their efficiency may vary based on tef genotypes or accessions used. [ABSTRACT FROM AUTHOR]

Copyright of Tropical Grasslands / Forrajes Tropicales is the property of International Centre for Tropical Agriculture - CIAT and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The seed coat colour variation of 70 common vetch genotypes were determined by using uniform colour scale (L⁎a⁎b⁎) and their possible correlation with seed yield parameters including the number of pods per plant, the number of seeds per pod, pod dimension, and seed yield (kg/da) was determined. The results revealed presence of highly significant (p<0.01) variations for both the seed yield and the seed coat colour parameters measured. The number of pods per plant, the number of seeds per pod, and seed yield ranged from 5.8 to 16.03, from 5.2 to 7.66, and from 143.37 to 531.1, respectively. The lightness value varied from 19.00 to 40.28 while chromaticity a⁎ and b⁎ values ranged from −0.16 to 8.99 and from 0.79 to 22.11, respectively. The highest correlation coefficients were determined between b⁎ and L⁎ (r=0.73), and a⁎ and L⁎ (r=0.55). The seed coat colour traits and seed yield parameters generally showed weak negative correlations. Seed yellowness (b⁎) and seed yield had correlation coefficient of −0.25, while correlation between L⁎ and seed yield was determined as −0.23. The results indicated that lightness and yellowness of seed coat may be used as an important parameter to prescreen high yield genotypes of common vetch. [ABSTRACT FROM AUTHOR]

Genetic diversity of 30 common vetch (Vicia sativa L.) lines and cultivars obtained from various resources or collected from natural flora of Turkey was evaluated by using 55 sequence-related amplified polymorphism (SRAP) and five inter-simple sequence repeat (ISSR) primer sets, and their nuclear DNA contents were determined by flow cytometer. A total of 188 polymorphic loci were detected, with an average of 3.62 loci per primer. The percentage of polymorphic loci was 82.1%. The polymorphism information content values ranged from 0.12 to 0.96, with an average of 0.63. The genetic distance coefficients were in the range of 0.112-0.627. Cluster analysis revealed that the 27 lines and three cultivars could be divided into two main groups. No polyploidy was detected within any vetch lines tested while significant (P, 0.0001) nuclear DNA content differences were determined. The present study revealed that fast and accurate fingerprinting analysis could be done using SRAP and ISSR markers, which indicated existing significant variation among common vetch lines and cultivars. [ABSTRACT FROM AUTHOR]

We have developed a novel method to overcome coat-imposed seed dormancy in legume plants. Seeds of Lupinus albus L. and Trifolium pratense L. were stored in a freezer at -80°C for a period of time and then immediately treated with or without hot water at 90°C for 5 seconds. Germination tests were carried out in darkness at 20 ± 1.0°C with four replications in a completely randomized design. Final germination percentage (FGP), germination rate, and synchrony of seeds were evaluated. The results showed that new approach of freeze-thaw scarification provided high percentage of germinations in white lupin (84.16%) and red clover (74.50%) seeds while control seeds had FGPs of 3.3% and 26.0%, respectively. The immediate thawing of frozen seeds in hot water for 5 seconds was found not only an effective and reliable but also the quickest seed treatment method to prevail against coat-imposed seed dormancy in legume species and may become operationally applicable to other plant species. [ABSTRACT FROM AUTHOR]

The Arabidopsis mutant axr1 is defective in both auxin and jasmonic acid responses. A screen for axr1-24 suppressors yielded sar1-5, an allele of previously described mutants that partially correct the auxin response defects in axr1. The new allele partially suppresses defects in jasmonate response in axr1. The JA concentration required for 50% inhibition of seedling root growth was 5--10 μM for axr1-24 sar1-5. This was at least 10-fold less than that required for axr-24, but 5- to 10-fold higher than for WT. In the axr1-24 background sar1-5 also partially restored resistance to the soil fungus Pythium irregulare, a trait known to require jasmonate signaling. The axr1-24 mutant was equally resistant to JA and JA-Ile, indicating that the defect is not in formation of the JA conjugate that is required for signaling. In contrast to axr1, the tir1-1 mutant that affects the same signaling pathway showed no resistance to jasmonates. Taken together, this evidence argues that the defects in jasmonate response seen in axr1 are not a secondary result of impaired auxin signaling, but that AXR1 functions directly in jasmonate response. Both AXR1 and SAR1 potentially help to coordinate the diverse activities of these 2 important plant signaling pathways. [ABSTRACT FROM AUTHOR]

The 2C nuclear DNA contents of 40 common vetch (Vicia sativa L.) lines and cultivars were determined by using both safflower (Carthamus tinctorius L.) and barley (Hordeum vulgare L.) as internal reference standards in flow cytometry analysis and correlated with plant morphological characters and 1000-seed weight. The t-test results showed a significant difference between the mean DNA values of the barley and safflower standards (t = -16.74, P = 0.0001). Data analysis also indicated significant (P < 0.01) intraspecific nuclear DNA content variation within the common vetch lines and cultivars for both internal standards used. The DNA content values ranged from 3.342 pg to 3.652 pg and from 3.600 pg to 4.002 pg for the internal standards of safflower and barley, respectively. The DNA differences within the internal standards were 0.310 pg and 0.402 pg for safflower and barley, respectively. The internal standard of barley constantly produced higher DNA content values than the values of safflower standard for all vetch lines and cultivars. Nuclear DNA content differences between 2 internal standards for the same plant material reached as high as 15.59% (0.540 pg), which is equivalent to 528.12 Mbp DNA. No significant correlations between 1000-seed weight and the nuclear DNA contents of barley (P < 0.51) or safflower (P < 0.76) were detected. [ABSTRACT FROM AUTHOR]

Response of auxin resistant mutant, axr1-24, on salt stress in primary root growth was tested over a range of NaCl concentrations and results were compared with wild type. The axr1-24 was more resistant to the inhibitory effect of any salt concentrations tested than wild type, except 128 mM NaCI. Total inhibition of root elongation was 62% and 70% for axr1-24 and wild type, respectively, at 64 mM NaCl. Exogenous application of salicylic acid (SA) or l-aminocyclopropane-l-carboxylic acid resulted in a significant increase in jasmonic acid (JA)-inducible allene oxide synthase (A OS) gene expression, while induction was severely reduced on axr1-24 seedlings treated with SA after 24 h. The results of this study provided a link between auxin and salt stress as well as SA and JA signaling through AXR1. [ABSTRACT FROM AUTHOR]

The objective of this work is to study whether inclusion of various stress related plant growth regulators into priming solution would improve germination and emergence of Kentucky bluegrass (Poa pratensis L.) seeds. Seeds were primed in 1, 2 or 3% KH2 PO4 for six days at 20 °C. Four replications of 100 seeds for germination and 50 seeds for emergence were arranged in a completely randomized design. Priming seeds in 1% KH2 PO4 significantly increased germination percentage compared to untreated seeds, although germination rate and synchrony were reduced. Inclusion of methyl jasmonate (MeJA, 1, 3, 5, or 10 µM), 1-aminocyclopropane-1-carboxylic acid (ACC, 1, 3, 5, or 10 µM) or benzyladenine (BA, 50, 100, 200, or 500 µM) into priming solution revealed that germination characteristics (germination percentage, rate, and synchrony) could be further improved by supplementing plant growth regulators (PGRs) into priming solution. The highest final germination percentage was obtained from the seeds primed in the presence of 500 µM BA (79 %) compared to seeds primed in 1 % KH2 PO4 (65 %) only. The PGRs improved final emergence percentage and the highest BA concentration was more effective compared to other PGRs tested. The results indicated that 1% KH2 PO4 supplemented with 500 µM BA could be used to promote germination of Poa pratensis L. seeds to some extend while 3 µM MeJA can be used to enhance seedling emergence rate of Kentucky bluegrass seeds. [ABSTRACT FROM AUTHOR]

Substantial evidence indicates that amino acid conjugates of indole-3-acetic acid (IAA) function in auxin homeostasis, yet the plant enzymes involved in their biosynthesis have not been identified. We tested whether several Arabidopsis thaliana enzymes that are related to the auxin-induced soybean (Glycine max) GH3 gene product synthesize IAA-amino acid conjugates. In vitro reactions with six recombinant GH3 enzymes produced IAA conjugates with several amino acids, based on thin layer chromatography. The identity of the Ala, Asp, Phe, and Trp conjugates was verified by gas chromatography-mass spectrometry. Insertional mutations in GH3.1, GH3.2, GH3.5, and GH3.17 resulted in modestly increased sensitivity to IAA in seedling root. Overexpression of GH3.6 in the activation-tagged mutant dfl1-D did not significantly alter IAA level but resulted in 3.2- and 4.5-fold more IAA-Asp than in wild-type seedlings and mature leaves, respectively. In addition to IAA, dfl1-D was less sensitive to indole-3-butyric acid and naphthaleneacetic acid, consistent with the fact that GH3.6 was active on each of these auxins. By contrast, GH3.6 and the other five enzymes tested were inactive on halogenated auxins, and dfl1-D was not resistant to these. This evidence establishes that several GH3 genes encode IAA-amido synthetases, which help to maintain auxin homeostasis by conjugating excess IAA to amino acids. [ABSTRACT FROM AUTHOR]

Plant growth and metabolism are affected by various biotic and abiotic stimuli including microorganisms and insects attack as well as light and environmental stresses. Such a diverse plant response requires a communication system that uses a group of chemical messengers called hormones. Hormones promote, inhibit, or qualitatively modify plant growth and development. This complex process requires a signal transduction that defines a specific information pathway within a cell that translates an intra- or extracellular signal into a specific cellular response. The characterization of mutants in the hormone response pathway provides not only an excellent opportunity to understand hormone action in plant physiology and development, but also helps to dissect the molecular genetics of hormone signaling pathways and to isolate the corresponding genes. This paper will introduce plant hormone signaling and mutants involved in signaling pathways in general, and will review recent progress in the molecular genetics of jasmonic acid signaling. [ABSTRACT FROM AUTHOR]

Despite its importance in a variety of plant defense responses, our understanding of how jasmonic acid (JA) functions at the biochemical level is limited. Several amino acid conjugates of JA were tested for their ability to complement the JA-insensitive Arabidopsis thaliana mutant jar1-1. Unlike free JA, JA-Ile inhibited root growth in jar1-1 to the same extent as in the wild type, whereas JA-Val, JA-Leu, and JA-Phe were ineffective inhibitors in both genotypes. Thin-layer chromatography and gas chromatography-mass spectrometry (GC-MS) analysis of products produced in vitro by recombinant JAR1 demonstrated that this enzyme forms JA-amido conjugates with several amino acids, including JA-Ile. JA-Val, -Leu, -Ile, and -Phe were each quantified in Arabidopsis seedlings by GC-MS. JA-Ile was found at 29.6 pmole g-1 fresh weight (FW) in the wild type but was more than sevenfold lower in two jar1 alleles. JA-Leu, -Val, and -Phe were present at only low levels in both genotypes. Expression of wild-type JAR1 in transgenic jar1-1 plants restored sensitivity to JA and elevated JA-Ile to the same level as in the wild type. The ethylene precursor 1-aminocyclopropane-l-carboxylic acid (ACC) conjugated to JA was also round in plant tissue at 18.4 pmole g-1 FW. JA-ACC was determined not be an effective jasmonate root inhibitor, and surprisingly, was twofold higher in the mutants than in the wild type. This suggests that another JA-conjugating enzyme(s) is present in Arabidopsis. Synthesis of JA-ACC might provide a mechanism to coregulate the availability of JA and ACC for conversion to the active hormones JA-Ile and ethylene, respectively. We conclude that JAR1 is a JA-amino synthetase that is required to activate JA for optimal signaling in Arabidopsis. Plant hormone activation by conjugation to amino acids and the enzymes involved in their formation were previously unknown. [ABSTRACT FROM AUTHOR]

Plants show their defence mechanism against pathogens and insects by induction of both localized and systemic responses. Of these, systemic acquired resistance (SAR) provides a protection on the uninfected tissues by activating different signaling pathways leading to induction of several pathogen related (PR) genes upon contact with invaders. Details of the molecular mechanisms of SAR, including pathogenesis-related proteins and their expression, and the signals including salicylic acid and jasmonates are still unclear. However, characterization of mutants involved in this response pathway helps to dissect this complex mechanism of SAR. In this paper, it will be discussed genes associated with SAR and the identification of mutants involved in this response pathway. [ABSTRACT FROM AUTHOR]

Plant Na + / H + antiporter ( NHX ) genes enhance salt tolerance by preventing excessive Na + accumulation in the cytosol through partitioning of Na + ions into vacuoles or extracellular transport across the plasma membrane. However, there is limited detailed information regarding the salt stress responsive SlNHX s in the most recent tomato genome. We investigated the role of this gene family's expression patterns in the open flower tissues under salt shock in Solanum lycopersicum using a genome-wide approach. A total of seven putative SlNHX genes located on chromosomes 1, 4, 6, and 10 were identified, but no ortholog of the NHX5 gene was identified in the tomato genome. Phylogenetic analysis revealed that these genes are divided into three different groups. SlNHX proteins with 10-12 transmembrane domains were hypothetically localized in vacuoles or cell membranes. Promoter analysis revealed that SlNHX6 and SlNHX8 are involved with the stress-related MeJA hormone in response to salt stress signaling. The structural motif analysis of SlNHX1, -2, -3, -4, and -6 proteins showed that they have highly conserved amiloride binding sites. The protein-protein network revealed that SlNHX7 and SlNHX8 interact physically with Salt Overly Sensitive (SOS) pathway proteins. Transcriptome analysis demonstrated that the SlNHX2 and SlNHX6 genes were substantially expressed in the open flower tissues. Moreover, quantitative PCR analysis indicated that all SlNHX genes, particularly SlNHX6 and SlNHX8 , are significantly upregulated by salt shock in the open flower tissues. Our results provide an updated framework for future genetic research and development of breeding strategies against salt stress in the tomato., Competing Interests: The authors declare that they have no conflict of interest., (© 2023 The Authors. Plant Direct published by American Society of Plant Biologists and the Society for Experimental Biology and John Wiley & Sons Ltd.)

A screen for Arabidopsis mutants that were insensitive to methyl jasmonate (MeJA) in an assay for seedling root growth yielded only alleles of previously isolated mutants jar1 and coi1, with one exception. Mapping of the locus and morphological characterization of the new mutant suggested it might be allelic to axr1, which had not previously been reported to show resistance to MeJA. The F(1) from a cross of the new mutant with axr1-3 did not show complementation, confirming that these are the same genes. The new allele is called axr1-24. In addition to MeJA and indole-3-acetic acid (IAA), axr1-24 had decreased sensitivity to 1-aminocyclopropane-1-carboxylic acid, 6-benzylamino-purine, epi-brassinolide, and abscisic acid. Both axr1-24 and the previously characterized axr1-3 allele were shown to be susceptible to the opportunistic pathogen Pythium irregulare, a trait found in other jasmonate response mutants, including jar1-1. The double mutant jar1-1/axr1-3 was more resistant to inhibition of root growth by MeJA and was more susceptible to P. irregulare infection than either single mutant, suggesting these genes might act in independent response pathways. In contrast, resistance to IAA in the double mutant was not different from axr1-3. Northern-blot analysis showed that IAA induced the jasmonate-responsive lipoxygenase 2, AOS, and AtVSP gene transcripts and induction was strongly impaired in axr1-3. However, transcript induction by MeJA was only minimally affected in axr1-3. This study demonstrates that in addition to auxin signaling, the AXR1 locus is involved in MeJA response, providing a mechanistic link between jasmonate and auxin-signaling pathways.

Jasmonic acid (JA) and related cyclopentanones are critical plant signaling molecules, but their mode of action at the molecular level is unclear. A map-based approach was used to identify the defective gene in the Arabidopsis JA response mutant jar1-1. JAR1 is 1 of 19 closely related Arabidopsis genes that are similar to the auxin-induced soybean GH3 gene. Analysis of fold predictions for this protein family suggested that JAR1 might belong to the acyl adenylate-forming firefly luciferase superfamily. These enzymes activate the carboxyl groups of a variety of substrates for their subsequent biochemical modification. An ATP-PPi isotope exchange assay was used to demonstrate adenylation activity in a glutathione S-transferase-JAR1 fusion protein. Activity was specific for JA, suggesting that covalent modification of JA is important for its function. Six other Arabidopsis genes were specifically active on indole-3-acetic acid (IAA), and one was active on both IAA and salicylic acid. These findings suggest that the JAR1 gene family is involved in multiple important plant signaling pathways.