Evolution and Expression of the Meprin and TRAF Homology Domain-Containing Gene Family in Solanaceae.

Meprin and TRAF homology (MATH)-domain-containing proteins are pivotal in modulating plant development and environmental stress responses. To date, members of the MATH gene family have been identified only in a few plant species, including Arabidopsis thaliana, Brassica rapa, maize, and rice, and the functions of this gene family in other economically important crops, especially the Solanaceae family, remain unclear. The present study identified and analyzed 58 MATH genes from three Solanaceae species, including tomato (Solanum lycopersicum), potato (Solanum tuberosum), and pepper (Capsicum annuum). Phylogenetic analysis and domain organization classified these MATH genes into four groups, consistent with those based on motif organization and gene structure. Synteny analysis found that segmental and tandem duplication might have contributed to MATH gene expansion in the tomato and the potato, respectively. Collinearity analysis revealed high conservation among Solanaceae MATH genes. Further cis-regulatory element prediction and gene expression analysis showed that Solanaceae MATH genes play essential roles during development and stress response. These findings provide a theoretical basis for other functional studies on Solanaceae MATH genes.

Poaceae-specific ß-1,3;1,4-d-glucans link jasmonate signalling to OsLecRK1-mediated defence response during rice-brown planthopper interactions.

Brown planthopper (BPH, Nilaparvata lugens), a highly destructive insect pest, poses a serious threat to rice (Oryza sativa) production worldwide. Jasmonates are key phytohormones that regulate plant defences against BPH; however, the molecular link between jasmonates and BPH responses in rice remains largely unknown. Here, we discovered a Poaceae-specific metabolite, mixed-linkage ß-1,3;1,4-d-glucan (MLG), which contributes to jasmonate-mediated BPH resistance. MLG levels in rice significantly increased upon BPH attack. Overexpressing OsCslF6, which encodes a glucan synthase that catalyses MLG biosynthesis, significantly enhanced BPH resistance and cell wall thickness in vascular bundles, whereas knockout of OsCslF6 reduced BPH resistance and vascular wall thickness. OsMYC2, a master transcription factor of jasmonate signalling, directly controlled the upregulation of OsCslF6 in response to BPH feeding. The AT-rich domain of the OsCslF6 promoter varies in rice varieties from different locations and natural variants in this domain were associated with BPH resistance. MLG-derived oligosaccharides bound to the plasma membrane-anchored LECTIN RECEPTOR KINASE1 OsLecRK1 and modulated its activity. Thus, our findings suggest that the OsMYC2-OsCslF6 module regulates pest resistance by modulating MLG production to enhance vascular wall thickness and OsLecRK1-mediated defence signalling during rice-BPH interactions.

Oxalic Acid Inhibits Feeding Behavior of the Brown Planthopper via Binding to Gustatory Receptor Gr23a.

Plants produce diverse secondary compounds as natural protection against microbial and insect attack. Most of these compounds, including bitters and acids, are sensed by insect gustatory receptors (Grs). Although some organic acids are attractive at low or moderate levels, most acidic compounds are potentially toxic to insects and repress food consumption at high concentrations. At present, the majority of the reported sour receptors function in appetitive behaviors rather than aversive taste responses. Here, using two different heterologous expression systems, the insect Sf9 cell line and the mammalian HEK293T cell line, we started from crude extracts of rice (Oryza sativa) and successfully identified oxalic acid (OA) as a ligand of NlGr23a, a Gr in the brown planthopper Nilaparvata lugens that feeds solely on rice. The antifeedant effect of OA on the brown planthopper was dose dependent, and NlGr23a mediated the repulsive responses to OA in both rice plants and artificial diets. To our knowledge, OA is the first identified ligand of Grs starting from plant crude extracts. These findings on rice-planthopper interactions will be of broad interest for pest control in agriculture and also for better understanding of how insects select host plants.

Overexpression of the Arabidopsis MACPF Protein AtMACP2 Promotes Pathogen Resistance by Activating SA Signaling.

Immune response in plants is tightly regulated by the coordination of the cell surface and intracellular receptors. In animals, the membrane attack complex/perforin-like (MACPF) protein superfamily creates oligomeric pore structures on the cell surface during pathogen infection. However, the function and molecular mechanism of MACPF proteins in plant pathogen responses remain largely unclear. In this study, we identified an Arabidopsis MACP2 and investigated the responsiveness of this protein during both bacterial and fungal pathogens. We suggest that MACP2 induces programmed cell death, bacterial pathogen resistance, and necrotrophic fungal pathogen sensitivity by activating the biosynthesis of tryptophan-derived indole glucosinolates and the salicylic acid signaling pathway dependent on the activity of enhanced disease susceptibility 1 (EDS1). Moreover, the response of MACP2 mRNA isoforms upon pathogen attack is differentially regulated by a posttranscriptional mechanism: alternative splicing. In comparison to previously reported MACPFs in Arabidopsis, MACP2 shares a redundant but nonoverlapping role in plant immunity. Thus, our findings provide novel insights and genetic tools for the MACPF family in maintaining SA accumulation in response to pathogens in Arabidopsis.

Phloem unloading via the apoplastic pathway is essential for shoot distribution of root-synthesized cytokinins.

Root-synthesized cytokinins are transported to the shoot and regulate the growth, development, and stress responses of aerial tissues. Previous studies have demonstrated that Arabidopsis (Arabidopsis thaliana) ATP binding cassette (ABC) transporter G family member 14 (AtABCG14) participates in xylem loading of root-synthesized cytokinins. However, the mechanism by which these root-derived cytokinins are distributed in the shoot remains unclear. Here, we revealed that AtABCG14-mediated phloem unloading through the apoplastic pathway is required for the appropriate shoot distribution of root-synthesized cytokinins in Arabidopsis. Wild-type rootstocks grafted to atabcg14 scions successfully restored trans-zeatin xylem loading. However, only low levels of root-synthesized cytokinins and induced shoot signaling were rescued. Reciprocal grafting and tissue-specific genetic complementation demonstrated that AtABCG14 disruption in the shoot considerably increased the retention of root-synthesized cytokinins in the phloem and substantially impaired their distribution in the leaf apoplast. The translocation of root-synthesized cytokinins from the xylem to the phloem and the subsequent unloading from the phloem is required for the shoot distribution and long-distance shootward transport of root-synthesized cytokinins. This study revealed a mechanism by which the phloem regulates systemic signaling of xylem-mediated transport of root-synthesized cytokinins from the root to the shoot.

Identification and Expression of the Multidrug and Toxic Compound Extrusion (MATE) Gene Family in Capsicum annuum and Solanum tuberosum.

Multidrug and Toxic Compound Extrusion (MATE) proteins are essential transporters that extrude metabolites and participate in plant development and the detoxification of toxins. Little is known about the MATE gene family in the Solanaceae, which includes species that produce a broad range of specialized metabolites. Here, we identified and analyzed the complement of MATE genes in pepper (Capsicum annuum) and potato (Solanum tuberosum). We classified all MATE genes into five groups based on their phylogenetic relationships and their gene and protein structures. Moreover, we discovered that tandem duplication contributed significantly to the expansion of the pepper MATE family, while both tandem and segmental duplications contributed to the expansion of the potato MATE family, indicating that MATEs took distinct evolutionary paths in these two Solanaceous species. Analysis of ω values showed that all potato and pepper MATE genes experienced purifying selection during evolution. In addition, collinearity analysis showed that MATE genes were highly conserved between pepper and potato. Analysis of cis-elements in MATE promoters and MATE expression patterns revealed that MATE proteins likely function in many stages of plant development, especially during fruit ripening, and when exposed to multiple stresses, consistent with the existence of functional differentiation between duplicated MATE genes. Together, our results lay the foundation for further characterization of pepper and potato MATE gene family members.

Evolution and Expression of the Membrane Attack Complex and Perforin Gene Family in the Poaceae.

Membrane Attack Complex and Perforin (MACPF) proteins play crucial roles in plant development and plant responses to environmental stresses. To date, only four MACPF genes have been identified in Arabidopsis thaliana, and the functions of the MACPF gene family members in other plants, especially in important crop plants, such as the Poaceae family, remain largely unknown. In this study, we identified and analyzed 42 MACPF genes from six completely sequenced and well annotated species representing the major Poaceae clades. A phylogenetic analysis of MACPF genes resolved four groups, characterized by shared motif organizations and gene structures within each group. MACPF genes were unevenly distributed along the Poaceae chromosomes. Moreover, segmental duplications and dispersed duplication events may have played significant roles during MACPF gene family expansion and functional diversification in the Poaceae. In addition, phylogenomic synteny analysis revealed a high degree of conservation among the Poaceae MACPF genes. In particular, Group I, II, and III MACPF genes were exposed to strong purifying selection with different evolutionary rates. Temporal and spatial expression analyses suggested that Group III MACPF genes were highly expressed relative to the other groups. In addition, most MACPF genes were highly expressed in vegetative tissues and up-regulated by several biotic and abiotic stresses. Taken together, these findings provide valuable information for further functional characterization and phenotypic validation of the Poaceae MACPF gene family.

Brassinosteroids Antagonize Jasmonate-Activated Plant Defense Responses through BRI1-EMS-SUPPRESSOR1 (BES1).

Brassinosteroids (BRs) and jasmonates (JAs) regulate plant growth, development, and defense responses, but how these phytohormones mediate the growth-defense tradeoff is unclear. Here, we identified the Arabidopsis (Arabidopsis thaliana) dwarf at early stages1 (dwe1) mutant, which exhibits enhanced expression of defensin genes PLANT DEFENSIN1.2a (PDF1.2a) and PDF1.2b The dwe1 mutant showed increased resistance to herbivory by beet armyworms (Spodoptera exigua) and infection by botrytis (Botrytis cinerea). DWE1 encodes ROTUNDIFOLIA3, a cytochrome P450 protein essential for BR biosynthesis. The JA-inducible transcription of PDF1.2a and PDF1.2b was significantly reduced in the BRASSINOSTEROID INSENSITIVE1-ETHYL METHANESULFONATE-SUPPRESSOR1 (BES1) gain-of-function mutant bes1- D, which was highly susceptible to S. exigua and B. cinerea BES1 directly targeted the terminator regions of PDF1.2a/PDF1.2b and suppressed their expression. PDF1.2a overexpression diminished the enhanced susceptibility of bes1- D to B. cinerea but did not improve resistance of bes1- D to S. exigua In response to S. exigua herbivory, BES1 inhibited biosynthesis of the JA-induced insect defense-related metabolite indolic glucosinolate by interacting with transcription factors MYB DOMAIN PROTEIN34 (MYB34), MYB51, and MYB122 and suppressing expression of genes encoding CYTOCHROME P450 FAMILY79 SUBFAMILY B POLYPEPTIDE3 (CYP79B3) and UDP-GLUCOSYL TRANSFERASE 74B1 (UGT74B1). Thus, BR contributes to the growth-defense tradeoff by suppressing expression of defensin and glucosinolate biosynthesis genes.

Autophagy regulates glucose-mediated root meristem activity by modulating ROS production in Arabidopsis.

Glucose produced from photosynthesis is a key nutrient signal regulating root meristem activity in plants; however, the underlying mechanisms remain poorly understood. Here, we show that, by modulating reactive oxygen species (ROS) levels, the conserved macroautophagy/autophagy degradation pathway contributes to glucose-regulated root meristem maintenance. In Arabidopsis thaliana roots, a short exposure to elevated glucose temporarily suppresses constitutive autophagosome formation. The autophagy-defective autophagy-related gene (atg) mutants have enhanced tolerance to glucose, established downstream of the glucose sensors, and accumulate less glucose-induced ROS in the root tips. Moreover, the enhanced root meristem activities in the atg mutants are associated with improved auxin gradients and auxin responses. By acting with AT4G39850/ABCD1 (ATP-binding cassette D1; Formerly PXA1/peroxisomal ABC transporter 1), autophagy plays an indispensable role in the glucose-promoted degradation of root peroxisomes, and the atg mutant phenotype is partially rescued by the overexpression of ABCD1. Together, our findings suggest that autophagy is an essential mechanism for glucose-mediated maintenance of the root meristem. Abbreviation: ABA: abscisic acid; ABCD1: ATP-binding cassette D1; ABO: ABA overly sensitive; AsA: ascorbic acid; ATG: autophagy related; CFP: cyan fluorescent protein; Co-IP: co-immunoprecipitation; DAB: 3',3'-diaininobenzidine; DCFH-DA: 2',7'-dichlorodihydrofluorescin diacetate; DR5: a synthetic auxin response element consists of tandem direct repeats of 11 bp that included the auxin-responsive TGTCTC element; DZ: differentiation zone; EZ, elongation zone; GFP, green fluorescent protein; GSH, glutathione; GUS: ß-glucuronidase; HXK1: hexokinase 1; H2O2: hydrogen peroxide; IAA: indole-3-acetic acid; IBA: indole-3-butyric acid; KIN10/11: SNF1 kinase homolog 10/11; MDC: monodansylcadaverine; MS: Murashige and Skoog; MZ: meristem zone; NBT: nitroblue tetrazolium; NPA: 1-N-naphtylphthalamic acid; OxIAA: 2-oxindole-3-acetic acid; PIN: PIN-FORMED; PLT: PLETHORA; QC: quiescent center; RGS1: Regulator of G-protein signaling 1; ROS: reactive oxygen species; SCR: SCARECROW; SHR, SHORT-ROOT; SKL: Ser-Lys-Leu; SnRK1: SNF1-related kinase 1; TOR: target of rapamycin; UPB1: UPBEAT1; WOX5: WUSCHEL related homeobox 5; Y2H: yeast two-hybrid; YFP: yellow fluorescent protein.

Jasmonate Regulates Plant Responses to Postsubmergence Reoxygenation through Transcriptional Activation of Antioxidant Synthesis.

Submergence induces hypoxia in plants; exposure to oxygen following submergence, termed reoxygenation, produces a burst of reactive oxygen species. The mechanisms of hypoxia sensing and signaling in plants have been well studied, but how plants respond to reoxygenation remains unclear. Here, we show that reoxygenation in Arabidopsis (Arabidopsis thaliana) involves rapid accumulation of jasmonates (JAs) and increased transcript levels of JA biosynthesis genes. Application of exogenous methyl jasmonate improved tolerance to reoxygenation in wild-type Arabidopsis; also, mutants deficient in JA biosynthesis and signaling were very sensitive to reoxygenation. Moreover, overexpression of the transcription factor gene MYC2 enhanced tolerance to posthypoxic stress, and myc2 knockout mutants showed increased sensitivity to reoxygenation, indicating that MYC2 functions as a key regulator in the JA-mediated reoxygenation response. MYC2 transcriptionally activates members of the VITAMIN C DEFECTIVE (VTC) and GLUTATHIONE SYNTHETASE (GSH) gene families, which encode rate-limiting enzymes in the ascorbate and glutathione synthesis pathways. Overexpression of VTC1 and GSH1 in the myc2-2 mutant suppressed the posthypoxic hypersensitive phenotype. The JA-inducible accumulation of antioxidants may alleviate oxidative damage caused by reoxygenation, improving plant survival after submergence. Taken together, our findings demonstrate that JA signaling interacts with the antioxidant pathway to regulate reoxygenation responses in Arabidopsis.

Jasmonate complements the function of Arabidopsis lipoxygenase3 in salinity stress response.

The functions of jasmonic acid (JA) in various stress responses have been uncovered in details, but its role in salt tolerance remains unclear. Here, we characterize the function of Arabidopsis lipoxygenase3 (LOX3), an enzyme involved in JA synthesis, in salt stress response. The transcriptional analysis indicated that LOX3 was dramatically induced under salt treatment. Compared with wild type, the lox3 mutant exhibited hypersensitivity to salt stress in germination and different developmental stages. Interestingly, methyl jasmonate (MeJA) rescued the salt sensitivity phenotypes of the lox3 mutant, suggesting the impairment of salinity response in the mutant may be mediated by JA. Furthermore, the lateral root number of the lox3 mutant was similar with that in wild type under normal condition, but less than that in wild type during salt treatment, and this lateral root sensitivity phenotype was also complemented by exogenous MeJA. In addition, the measurement of oxylipins in the lox3 mutant and the analysis on germination of the JA receptor coi1 mutant under salt stress supported that JA may regulate the early response to salinity. In conclusion, we characterized the novel function of LOX3 in salinity stress response, and found that the salt hypersensitivity of the lox3 mutant can be complemented by MeJA, providing new evidence for the association between JA and salt tolerance.