Trichoderma virens and Pseudomonas chlororaphis Differentially Regulate Maize Resistance to Anthracnose Leaf Blight and Insect Herbivores When Grown in Sterile versus Non-Sterile Soils.

Soil-borne Trichoderma spp. have been extensively studied for their biocontrol activities against pathogens and growth promotion ability in plants. However, the beneficial effect of Trichoderma on inducing resistance against insect herbivores has been underexplored. Among diverse Trichoderma species, consistent with previous reports, we showed that root colonization by T. virens triggered induced systemic resistance (ISR) to the leaf-infecting hemibiotrophic fungal pathogens Colletotrichum graminicola. Whether T. virens induces ISR to insect pests has not been tested before. In this study, we investigated whether T. virens affects jasmonic acid (JA) biosynthesis and defense against fall armyworm (FAW) and western corn rootworm (WCR). Unexpectedly, the results showed that T. virens colonization of maize seedlings grown in autoclaved soil suppressed wound-induced production of JA, resulting in reduced resistance to FAW. Similarly, the bacterial endophyte Pseudomonas chlororaphis 30-84 was found to suppress systemic resistance to FAW due to reduced JA. Further comparative analyses of the systemic effects of these endophytes when applied in sterile or non-sterile field soil showed that both T. virens and P. chlororaphis 30-84 triggered ISR against C. graminicola in both soil conditions, but only suppressed JA production and resistance to FAW in sterile soil, while no significant impact was observed when applied in non-sterile soil. In contrast to the effect on FAW defense, T. virens colonization of maize roots suppressed WCR larvae survival and weight gain. This is the first report suggesting the potential role of T. virens as a biocontrol agent against WCR.

Duplicated Copy Number Variant of the Maize 9-Lipoxygenase ZmLOX5 Improves 9,10-KODA-Mediated Resistance to Fall Armyworms.

Extensive genome structure variations, such as copy number variations (CNVs) and presence/absence variations, are the basis for the remarkable genetic diversity of maize; however, the effect of CNVs on maize herbivory defense remains largely underexplored. Here, we report that the naturally occurring duplication of the maize 9-lipoxygenase gene ZmLOX5 leads to increased resistance of maize to herbivory by fall armyworms (FAWs). Previously, we showed that ZmLOX5-derived oxylipins are required for defense against chewing insect herbivores and identified several inbred lines, including Yu796, that contained duplicated CNVs of ZmLOX5, referred to as Yu796-2×LOX5. To test whether introgression of the Yu796-2×LOX5 locus into a herbivore-susceptible B73 background that contains a single ZmLOX5 gene is a feasible approach to increase resistance, we generated a series of near-isogenic lines that contained either two, one, or zero copies of the Yu796-2×LOX5 locus in the B73 background via six backcrosses (BC6). Droplet digital PCR (ddPCR) confirmed the successful introgression of the Yu796-2×LOX5 locus in B73. The resulting B73-2×LOX5 inbred line displayed increased resistance against FAW, associated with increased expression of ZmLOX5, increased wound-induced production of its primary oxylipin product, the α-ketol, 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (9,10-KODA), and the downstream defense hormones regulated by this molecule, 12-oxo-phytodienoic acid (12-OPDA) and abscisic acid (ABA). Surprisingly, wound-induced JA-Ile production was not increased in B73-2×LOX5, resulting from the increased JA catabolism. Furthermore, B73-2×LOX5 displayed reduced water loss in response to drought stress, likely due to increased ABA and 12-OPDA content. Taken together, this study revealed that the duplicated CNV of ZmLOX5 quantitively contributes to maize antiherbivore defense and presents proof-of-concept evidence that the introgression of naturally occurring duplicated CNVs of a defensive gene into productive but susceptible crop varieties is a feasible breeding approach for enhancing plant resistance to herbivory and tolerance to abiotic stress.

Maize OPR2 and LOX10 Mediate Defense against Fall Armyworm and Western Corn Rootworm by Tissue-Specific Regulation of Jasmonic Acid and Ketol Metabolism.

Foliage-feeding fall armyworm (FAW; Spodoptera frugiperda) and root-feeding western corn rootworm (WCR; Diabrotica virgifera virgifera) are maize (Zea mays L.) pests that cause significant yield losses. Jasmonic acid (JA) plays a pivotal defense role against insects. 12-oxo-phytodienoic acid (12-OPDA) is converted into JA by peroxisome-localized OPDA reductases (OPR). However, little is known about the physiological functions of cytoplasmic OPRs. Here, we show that disruption of ZmOPR2 reduced wound-induced JA production and defense against FAW while accumulating more JA catabolites. Overexpression of ZmOPR2 in Arabidopsis enhanced JA production and defense against beet armyworm (BAW; Spodoptera exigua). In addition, lox10opr2 double mutants were more susceptible than either single mutant, suggesting that ZmOPR2 and ZmLOX10 uniquely and additively contributed to defense. In contrast to the defensive roles of ZmOPR2 and ZmLOX10 in leaves, single mutants did not display any alteration in root herbivory defense against WCR. Feeding on lox10opr2 double mutants resulted in increased WCR mortality associated with greater herbivory-induced production of insecticidal death acids and ketols. Thus, ZmOPR2 and ZmLOX10 cooperatively inhibit the synthesis of these metabolites during herbivory by WCR. We conclude that ZmOPR2 and ZmLOX10 regulate JA-mediated resistance in leaves against FAW while suppressing insecticidal oxylipin synthesis in roots during WCR infestation.

9,10-KODA, an α-ketol produced by the tonoplast-localized 9-lipoxygenase ZmLOX5, plays a signaling role in maize defense against insect herbivory.

13-Lipoxygenases (LOXs) initiate the synthesis of jasmonic acid (JA), the best-understood oxylipin hormone in herbivory defense. However, the roles of 9-LOX-derived oxylipins in insect resistance remain unclear. Here, we report a novel anti-herbivory mechanism mediated by a tonoplast-localized 9-LOX, ZmLOX5, and its linolenic acid-derived product, 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (9,10-KODA). Transposon-insertional disruption of ZmLOX5 resulted in the loss of resistance to insect herbivory. lox5 knockout mutants displayed greatly reduced wound-induced accumulation of multiple oxylipins and defense metabolites, including benzoxazinoids, abscisic acid (ABA), and JA-isoleucine (JA-Ile). However, exogenous JA-Ile failed to rescue insect defense in lox5 mutants, while applications of 1 µM 9,10-KODA or the JA precursor, 12-oxo-phytodienoic acid (12-OPDA), restored wild-type resistance levels. Metabolite profiling revealed that exogenous 9,10-KODA primed the plants for increased production of ABA and 12-OPDA, but not JA-Ile. While none of the 9-oxylipins were able to rescue JA-Ile induction, the lox5 mutant accumulated lower wound-induced levels of Ca2+, suggesting this as a potential explanation for lower wound-induced JA. Seedlings pretreated with 9,10-KODA exhibited rapid or more robust wound-induced defense gene expression. In addition, an artificial diet supplemented with 9,10-KODA arrested fall armyworm larvae growth. Finally, analysis of single and double lox5 and lox10 mutants showed that ZmLOX5 also contributed to insect defense by modulating ZmLOX10-mediated green leaf volatile signaling. Collectively, our study uncovered a previously unknown anti-herbivore defense and hormone-like signaling activity for a major 9-oxylipin α-ketol.

A non-JA producing oxophytodienoate reductase functions in salicylic acid-mediated antagonism with jasmonic acid during pathogen attack.

Peroxisome-localized oxo-phytodienoic acid (OPDA) reductases (OPR) are enzymes converting 12-OPDA into jasmonic acid (JA). However, the biochemical and physiological functions of the cytoplasmic non-JA producing OPRs remain largely unknown. Here, we generated Mutator-insertional mutants of the maize OPR2 gene and tested its role in resistance to pathogens with distinct lifestyles. Functional analyses showed that the opr2 mutants were more susceptible to the (hemi)biotrophic pathogens Colletotrichum graminicola and Ustilago maydis, but were more resistant to the necrotrophic fungus Cochliobolus heterostrophus. Hormone profiling revealed that increased susceptibility to C. graminicola was associated with decreased salicylic acid (SA) but increased JA levels. Mutation of the JA-producing lipoxygenase 10 (LOX10) reversed this phenotype in the opr2 mutant background, corroborating the notion that JA promotes susceptibility to this pathogen. Exogenous SA did not rescue normal resistance levels in opr2 mutants, suggesting that this SA-inducible gene is the key downstream component of the SA-mediated defences against C. graminicola. Disease assays of the single and double opr2 and lox10 mutants and the JA-deficient opr7opr8 mutants showed that OPR2 negatively regulates JA biosynthesis, and that JA is required for resistance against C. heterostrophus. Overall, this study uncovers a novel function of a non-JA producing OPR as a major negative regulator of JA biosynthesis during pathogen infection, a function that leads to its contrasting contribution to either resistance or susceptibility depending on pathogen lifestyle.

Transcriptome and Oxylipin Profiling Joint Analysis Reveals Opposite Roles of 9-Oxylipins and Jasmonic Acid in Maize Resistance to Gibberella Stalk Rot.

Gibberella stalk rot caused by Fusarium graminearum is one of the devastating diseases of maize that causes significant yield losses worldwide. The molecular mechanisms regulating defense against this pathogen remain poorly understood. According to recent studies, a major oxylipin hormone produced by 13-lipoxygenases (LOX) namely jasmonic acid (JA) has been associated with maize susceptibility to GSR. However, the specific roles of numerous 9-LOX-derived oxylipins in defense against Gibberella stalk rot (GSR) remain unexplained. In this study, we have shown that disruption of a 9-LOX gene, ZmLOX5, resulted in increased susceptibility to GSR, indicating its role in defense. To understand how ZmLOX5 regulates GSR resistance, we conducted transcriptome and oxylipin profiling using a zmlox5-3 mutant and near-isogenic wild type B73, upon infection with F. graminearum. The results showed that JA biosynthetic pathway genes were highly up-regulated, whereas multiple 9-LOX pathway genes were down-regulated in the infected zmlox5-3 mutant. Furthermore, oxylipin profiling of the mutant revealed significantly higher contents of several jasmonates but relatively lower levels of 9-oxylipins in zmlox5-3 upon infection. In contrast, B73 and W438, a more resistant inbred line, displayed relatively lower levels of JAs, but a considerable increase of 9-oxylipins. These results suggest antagonistic interaction between 9-oxylipins and JAs, wherein 9-oxylipins contribute to resistance while JAs facilitate susceptibility to F. graminearum.

Raman Spectroscopy as a Robust New Tool for Rapid and Accurate Evaluation of Drought Tolerance Levels in Both Genetically Diverse and Near-Isogenic Maize Lines.

Improving drought tolerance of crops has become crucial due to the current scenario of rapid climate change. In particular, development of new maize germplasm with increased drought tolerance is viewed as a major breeding goal to ensure sustainable food and feed production. Therefore, accurate rapid phenotyping techniques for selection of superior maize genotypes are required. The objectives of this study were to determine whether Raman microscopy technique can be applied for accurate assessment of drought-tolerance levels in both genetically diverse and near-isogenic maize lines that differ in their levels of drought-tolerance. Carotenoid degradation is known to be a direct stress response initiated by reactive oxygen species during osmotic stress such as drought. Using Raman mapping, we observed real-time changes in the rate of carotenoid degradation in chloroplasts that was dependent on the strength of osmotic stress. In addition, we showed that the rate of carotenoid degradation as measured by Raman spectroscopy correlates directly with drought tolerance levels of diverse maize genotypes. We conclude that Raman technique is a robust, biochemically selective and non-invasive phenotyping technique that accurately distinguishes drought tolerance levels in both genetically diverse and near-isogenic maize genotypes. We conclude that this technique can be further developed to render it suitable for field-based early assessment of breeding materials with superior drought-tolerance traits.

Genome-Wide Characterization of Jasmonates Signaling Components Reveals the Essential Role of ZmCOI1a-ZmJAZ15 Action Module in Regulating Maize Immunity to Gibberella Stalk Rot.

Gibberella stalk rot (GSR) by Fusarium graminearum causes significant losses of maize production worldwide. Jasmonates (JAs) have been broadly known in regulating defense against pathogens through the homeostasis of active JAs and COI-JAZ-MYC function module. However, the functions of different molecular species of JAs and COI-JAZ-MYC module in maize interactions with Fusarium graminearum and regulation of diverse metabolites remain unknown. In this study, we found that exogenous application of MeJA strongly enhanced resistance to GSR. RNA-seq analysis showed that MeJA activated multiple genes in JA pathways, which prompted us to perform a genome-wide screening of key JA signaling components in maize. Yeast Two-Hybrid, Split-Luciferase, and Pull-down assays revealed that the JA functional and structural mimic coronatine (COR) functions as an essential ligand to trigger the interaction between ZmCOIa and ZmJAZ15. By deploying CRISPR-cas9 knockout and Mutator insertional mutants, we demonstrated that coi1a mutant is more resistant, whereas jaz15 mutant is more susceptible to GSR. Moreover, JA-deficient opr7-5opr8-2 mutant displayed enhanced resistance to GSR compared to wild type. Together, these results provide strong evidence that ZmJAZ15 plays a pivotal role, whereas ZmCOIa and endogenous JA itself might function as susceptibility factors, in maize immunity to GSR.

Trichoderma virens colonization of maize roots triggers rapid accumulation of 12-oxophytodienoate and two ᵧ-ketols in leaves as priming agents of induced systemic resistance.

Two oxylipins 12-OPDA (12-Oxo-10(Z),15(Z)-phytodienoic acid) and an ᵧ-ketol, 9,10-KODA (10-oxo-9-hydroxy-12(Z), 15(Z)-octadecadienoic acid) were recently identified as important long-distance-induced systemic resistance (ISR) signals in Trichoderma virens-treated maize. On the other hand, jasmonic acid (JA), long believed to be a major signal of ISR, was not involved, as the JA-deficient mutant, opr7 opr8, retained the capacity for T. virens-triggered ISR. In order to further understand the biochemical basis for ISR priming in maize leaves, diverse oxylipins and phytohormones in the leaves of wild-type maize or ISR-deficient lox10-3 mutants treated with T. virens were quantified. This analysis revealed that 12-OPDA and two novel ᵧ-ketols, 9,12-KOMA (12-Oxo-9-hydroxy-10(E)-octadecenoic acid) and 9,12-KODA (12-Oxo-9-hydroxy-10(E),15(Z)-octadecadienoic acid), accumulated at high levels in ISR-positive plants. In support of the notion that 12-OPDA serves as a priming agent for ISR in addition to being a xylem-mobile signal, leaf pretreatment with this JA precursor resulted in increased resistance to Colletotrichum graminicola. Furthermore, the injection of 9,12-KODA or 9,12-KOMA in wild-type plants enhanced resistance against C. graminicola infection, suggesting that they play roles in ISR priming.

Relative contribution of LOX10, green leaf volatiles and JA to wound-induced local and systemic oxylipin and hormone signature in Zea mays (maize).

Green leaf volatiles (GLVs) and jasmonates (JAs) are the best-characterized groups of fatty acid-derived oxylipin signals that regulate wound-associated defenses. Beyond these two major groups of defense signals, plants produce an array of oxylipins in response to wounding, which possess potent signaling and/or insecticidal activities. In this study, we assessed the relative contribution of JAs and GLVs to wound-induced systemic signaling and the associated regulation of oxylipins in local and systemic tissues of maize (Zea mays). For this, we utilized GLV- and JA-deficient mutants, lox10 single and opr7opr8 double mutants, respectively, and profiled oxylipins in untreated leaves and roots, and in locally wounded and systemic leaves. In contrast to the studies in dicots, no systemic induction of JAs was observed in maize. Instead, a JA precursor, 12-OPDA, as well as ketols and C12/13 oxo-acids derived from 13-lipoxygenases (LOXs), were preferentially induced in both locally wounded and systemic unwounded leaves. Several 9-LOX-derived oxylipins (9-oxylipins) including hydroxides and ketones were also significantly induced locally. JA and JA-isoleucine (JA-Ile) were rapidly induced within 0.5 h, and were followed by a second increase in local tissue 4 h after wounding. GLV-deficient lox10 mutants displayed reduced levels of most 13-oxylipins, and elevated levels of several 9-oxylipins and the a-dioxygenase (DOX) product, 2-HOD. lox10 mutants were completely devoid of C6 volatiles and their C12 counterparts, and greatly decreased in C5 volatiles and their C13 oxo-acid counterparts. Thus, in addition to being the sole LOX isoform providing substrate for GLV synthesis, LOX10 is a major 13-LOX that provides substrate to several LOX branches that produce an array of 13-oxylipin products, including C5 volatiles. Interestingly, the rapid JA and JA-Ile increase at 0.5-2 h post-wounding was only moderately affected by the LOX10 mutation, while significantly reduced levels were observed at 4 h post-wounding. Combined with the previous findings that GLVs activate JA biosynthesis, these results suggest that both LOX10-derived substrates and/or GLVs are involved in the large second phase of JA synthesis proximal to the wound. Analyses of opr7opr8 mutants revealed that wound-induced oxylipin responses were positively regulated by JA signaling. The local and systemic accumulation of SA was not altered in the two mutants. Collectively, our results identified a subset of oxylipins strongly induced in wounded and systemic leaves, but their impact on insect defenses remain elusive. The lack of systemic induction of JAs points to substantial difference between systemic wound responses in studied dicots and maize. Our results show that GLV-deficiency and reduced JA in lox10 mutants had a greater impact on wound-induced local and systemic tissue oxylipin responses compared to the solely JA-deficient opr7opr8 double mutants. This suggests that GLVs or other LOX10-derived products heavily contribute to overall basal and wound-induced oxylipin responses. The specific roles of the GLV- and/or JA-dependent oxylipins in wound responses and defense remain to be further investigated by a combination of multiple orders of oxylipin-deficient mutants.

12-Oxo-Phytodienoic Acid Acts as a Regulator of Maize Defense against Corn Leaf Aphid.

The corn leaf aphid (CLA; Rhopalosiphum maidis) is a phloem sap-sucking insect that attacks many cereal crops, including maize (Zea mays). We previously showed that the maize inbred line Mp708, which was developed by classical plant breeding, provides enhanced resistance to CLA. Here, using electrophysiological monitoring of aphid feeding behavior, we demonstrate that Mp708 provides phloem-mediated resistance to CLA. Furthermore, feeding by CLA on Mp708 plants enhanced callose deposition, a potential defense mechanism utilized by plants to limit aphid feeding and subsequent colonization. In maize, benzoxazinoids (BX) or BX-derived metabolites contribute to enhanced callose deposition by providing heightened resistance to CLA. However, BX and BX-derived metabolites were not significantly altered in CLA-infested Mp708 plants, indicating BX-independent defense against CLA. Evidence presented here suggests that the constitutively higher levels of 12-oxo-phytodienoic acid (OPDA) in Mp708 plants contributed to enhanced callose accumulation and heightened CLA resistance. OPDA enhanced the expression of ethylene biosynthesis and receptor genes, and the synergistic interactions of OPDA and CLA feeding significantly induced the expression of the transcripts encoding Maize insect resistance1-Cysteine Protease, a key defensive protein against insect pests, in Mp708 plants. Furthermore, exogenous application of OPDA on maize jasmonic acid-deficient plants caused enhanced callose accumulation and heightened resistance to CLA, suggesting that the OPDA-mediated resistance to CLA is independent of the jasmonic acid pathway. We further demonstrate that the signaling function of OPDA, rather than a direct toxic effect, contributes to enhanced CLA resistance in Mp708.

Genome wide association study for drought, aflatoxin resistance, and important agronomic traits of maize hybrids in the sub-tropics.

The primary maize (Zea mays L.) production areas are in temperate regions throughout the world and this is where most maize breeding is focused. Important but lower yielding maize growing regions such as the sub-tropics experience unique challenges, the greatest of which are drought stress and aflatoxin contamination. Here we used a diversity panel consisting of 346 maize inbred lines originating in temperate, sub-tropical and tropical areas testcrossed to stiff-stalk line Tx714 to investigate these traits. Testcross hybrids were evaluated under irrigated and non-irrigated trials for yield, plant height, ear height, days to anthesis, days to silking and other agronomic traits. Irrigated trials were also inoculated with Aspergillus flavus and evaluated for aflatoxin content. Diverse maize testcrosses out-yielded commercial checks in most trials, which indicated the potential for genetic diversity to improve sub-tropical breeding programs. To identify genomic regions associated with yield, aflatoxin resistance and other important agronomic traits, a genome wide association analysis was performed. Using 60,000 SNPs, this study found 10 quantitative trait variants for grain yield, plant and ear height, and flowering time after stringent multiple test corrections, and after fitting different models. Three of these variants explained 5-10% of the variation in grain yield under both water conditions. Multiple identified SNPs co-localized with previously reported QTL, which narrows the possible location of causal polymorphisms. Novel significant SNPs were also identified. This study demonstrated the potential to use genome wide association studies to identify major variants of quantitative and complex traits such as yield under drought that are still segregating between elite inbred lines.

New perspectives into jasmonate roles in maize.

It is well-known from the model dicotyledonous plants, Arabidopsis and tomato, that jasmonates (JAs) act as defense hormones in planta due to their potent ability to mediate defensive responses against insect/pathogen attacks or harsh environmental conditions. JA is also required for various developmental processes such as male fertility, seed maturation, root extension, and leaf senescence. In our recently published Plant Cell paper, the multiple roles of JA in the monocotyledonous agro-economically important model plant, maize, were investigated by comprehensive analysis of JA-deficient double mutant disrupted in the two oxophytodienoate reductase genes, OPR7 and OPR8. These two genes are the closest orthologs of the Arabidopsis JA-producing OPR3 and are the only maize OPRs required for JA biosynthesis. With this mutant, we previously showed that JA is essential for both male and female reproductive development, and required for the regulation of brace root pigmentation, leaf senescence, and defense against oomycete Pythium aristosporum, and beet armyworm (Spodoptera exigua). In this addendum, we expanded the investigation into the function of JA in elongation of sheaths, leaves, and roots, and its involvement in photomorphogenesis of seedlings.

The novel monocot-specific 9-lipoxygenase ZmLOX12 is required to mount an effective jasmonate-mediated defense against Fusarium verticillioides in maize.

Fusarium verticillioides is a major limiting factor for maize production due to ear and stalk rot and the contamination of seed with the carcinogenic mycotoxin fumonisin. While lipoxygenase (LOX)-derived oxylipins have been implicated in defense against diverse pathogens, their function in maize resistance against F. verticillioides is poorly understood. Here, we functionally characterized a novel maize 9-LOX gene, ZmLOX12. This gene is distantly related to known dicot LOX genes, with closest homologs found exclusively in other monocot species. ZmLOX12 is predominantly expressed in mesocotyls in which it is strongly induced in response to F. verticillioides infection. The Mutator transposon-insertional lox12-1 mutant is more susceptible to F. verticillioides colonization of mesocotyls, stalks, and kernels. The infected mutant kernels accumulate a significantly greater amount of the mycotoxin fumonisin. Reduced resistance to the pathogen is accompanied by diminished levels of the jasmonic acid (JA) precursor 12-oxo phytodienoic acid, JA-isoleucine, and expression of jasmonate-biosynthetic genes. Supporting the strong defense role of jasmonates, the JA-deficient opr7 opr8 double mutant displayed complete lack of immunity to F. verticillioides. Unexpectedly, the more susceptible lox12 mutant accumulated higher levels of kauralexins, suggesting that F. verticillioides is tolerant to this group of antimicrobial phytoalexins. This study demonstrates that this unique monocot-specific 9-LOX plays a key role in defense against F. verticillioides in diverse maize tissues and provides genetic evidence that JA is the major defense hormone against this pathogen.

Transposon mutagenesis reveals differential pathogenesis of Ralstonia solanacearum on tomato and Arabidopsis.

Ralstonia solanacearum causes a deadly wilting disease on a wide range of crops. To elucidate pathogenesis of this bacterium in different host plants, we set out to identify R. solanacearum genes involved in pathogenesis by screening random transposon insertion mutants of a highly virulent strain, Pss190, on tomato and Arabidopsis thaliana. Mutants exhibiting various decreased virulence levels on these two hosts were identified. Sequence analysis showed that most, but not all, of the identified pathogenesis genes are conserved among distinct R. solanacearum strains. A few of the disrupted loci were not reported previously as being involved in R. solanacearum pathogenesis. Notably, a group of mutants exhibited differential pathogenesis on tomato and Arabidopsis. These results were confirmed by characterizing allelic mutants in one other R. solanacearum strain of the same phylotype. The significantly decreased mutants' colonization in Arabidopsis was found to be correlated with differential pathogenesis on these two plants. Differential requirement of virulence genes suggests adaptation of this bacterium in different host environments. Together, this study reveals commonalities and differences of R. solanacearum pathogenesis on single solanaceous and nonsolanaceous hosts, and provides important new insights into interactions between R. solanacearum and different host plants.