Lipid metabolism is differentially modulated by salicylic acid and heptanoyl salicylic acid during the induction of resistance in wheat against powdery mildew

Heptanoyl salicylic acid (HSA) is a salicylic acid (SA) derivative obtained by esterification of 2-OH benzoic acid with heptanoic acid. In wheat, the protection levels obtained against Blumeria graminis f. sp. tritici (Bgt) increased from 50% with SA to 95% with HSA. Using molecular, biochemical and cytological approaches, we investigated here how wheat lipid metabolism is differentially activated by SA and HSA in both infectious and non-infectious conditions, and how Bgt infectious process is altered by both inducers. First, in the absence of Bgt, continuous lipoxygenase (LOX)-encoding gene expression and corresponding activity were specifically induced by HSA. Moreover, compared to SA, HSA treatment resulted in earlier up-regulations of the phospholipase C2-encoding gene expression and it specifically affected the expression of a lipid transfer protein-encoding gene. In infectious context, both HSA and SA sprayings impaired penetration events and therefore haustorium formation, leading to less frequent fungal colonies. While this alteration only slowed down the evolution of Bgt infectious process in SA-sprayed leaves, it completely impaired the establishment of successful infectious events in HSA-sprayed leaves. In addition, HSA induced continuous increases of a LOX-encoding gene expression and of the corresponding LOX activity when compared to SA-sprayed leaves. Lipid metabolism is therefore overall highly responsive to HSA spraying and could represent effective defence mechanism triggered during the induction of resistance in wheat toward Bgt. The concepts of priming and energy costs of the defences induced by SA and HSA are also discussed.     

Systemic acquired resistance in Cavendish banana induced by infection with an incompatible strain of Fusarium oxysporum f. sp. cubense

Fusarium wilt of banana is caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). The fact that there are no economically viable biological, chemical, or cultural measures of controlling the disease in an infected field leads to search for alternative strategies involving activation of the plant's innate defense system. The mechanisms underlying systemic acquired resistance (SAR) are much less understood in monocots than in dicots. Since systemic protection of plants by attenuated or avirulent pathogens is a typical SAR response, the establishment of a biologically induced SAR model in banana is helpful to investigate the mechanism of SAR to Fusarium wilt. This paper described one such model using incompatible Foc race 1 to induce resistance against Foc tropical race 4 in an in vitro pathosystem. Consistent with the observation that the SAR provided the highest level of protection when the time interval between primary infection and challenge inoculation was 10 d, the activities of defense-related enzymes such as phenylalanine ammonia lyase (PAL, EC 4.3.1.5), peroxidase (POD, EC 1.11.1.7), polyphenol oxidase (PPO, EC 1.14.18.1), and superoxide dismutase (SOD, EC 1.15.1.1) in systemic tissues also reached the maximum level and were 2.00–2.43 times higher than that of the corresponding controls on the tenth day. The total salicylic acid (SA) content in roots of banana plantlets increased from about 1 to more than 5 μg g⁻¹ FW after the second leaf being inoculated with Foc race 1. The systemic up-regulation of MaNPR1A and MaNPR1B was followed by the second up-regulation of PR-1 and PR-3. Although SA and jasmonic acid (JA)/ethylene (ET) signaling are mostly antagonistic, systemic expression of PR genes regulated by different signaling pathways were simultaneously up-regulated after primary infection, indicating that both pathways are involved in the activation of the SAR.     

BTH和SA处理及白粉菌接种对甜瓜叶片光合特性的影响

以抗病品种Tam Dew和感病品种卡拉克赛为材料,研究了BTH和SA处理及白粉菌接种对甜瓜叶片叶面积、叶绿素含量、净光合速率、气孔导度、胞间CO2浓度的影响.结果表明,BTH和SA处理及白粉菌接种对甜瓜苗期叶面积扩展无显著影响;BTH和SA处理植株的叶片(第3叶)和新生叶片(第5叶)的净光合速率、叶绿素含量和气孔导度显著高于对照;白粉菌接种后,2个甜瓜叶片的叶绿素含量、净光合速率和气孔导度显著降低,而BTH和SA处理能缓解由白粉菌接种带来的叶绿素含量、净光合速率和气孔导度的下降趋势.说明BTH和SA处理能延长甜瓜叶片的光合寿命,延缓甜瓜叶片的叶绿素含量、净光合速率和气孔导度的下降趋势.     

Comparison of different constitutive and inducible promoters for the overexpression of transgenes in Arabidopsis thaliana

We compared the organ specificity and the strength of different constitutive (CaMV-35S, CaMV-35Somega, Arabidopsis ubiquitin UBQ1, and barley leaf thionin BTH6 promoter) and one inducible promoter (soybean heat-shock promoter Gmshp17.3) in stably transformed Arabidopsis thaliana plants. For this purpose we constructed a set of plant expression vectors equipped with the different promoters. Using the uidA reporter gene we could show that the CaMV-35S promoter has the highest expression level which was enhanced two-to threefold by the addition of a translational enhancer (TMV omega element) without altering the organ specificity of the promoter. The barley leaf thionin promoter was almost inactive in the majority of lines whereas the ubiquitin promoter exhibited an intermediate strength. The heat-shock promoter was inducible up to 18-fold but absolute levels were lower than in the case of the ubiquitin promoter. Conclusive quantitative results for different organs and developmental stages were obtained by the analysis of 24 stably transformed lines per promoter construct.     

Effects of divalent cations on bovine testicular hyaluronidase catalyzed transglycosylation of chondroitin sulfates

Glycosaminoglycans were prepared as salts of different divalent cations and tested as donors in bovine testicular hyaluronidase catalyzed transglycosylation reactions. All of the metal cations examined had similar binding efficiency of divalent cations to hyaluronan. However, cations bound with different efficiencies to chondroitin sulfate species and the differences were marked in the case of chondroitin 6-sulfate; the numbers of cations bound per disaccharide unit were estimated to be 0.075 for Mn, 1.231 for Ba, 0.144 for Zn, and 0.395 for Cu. While barium salt of chondroitin sulfates enhanced transglycosylation, the zinc salt of chondroitin sulfates inhibited transglycosylation. Therefore, by selecting the proper divalent cation salt of chondroitin sulfates as a donor in the transglycosylation reaction it is possible to improve the yields of the products.     

Enhanced disease resistance and hypersensitivity to BTH by introduction of an NH1/OsNPR1 paralog

Non‐expresser of pathogenesis‐related genes 1 (NPR1) is the master regulator of salicylic acid‐mediated systemic acquired resistance. Over‐expression of Arabidopsis NPR1 and rice NH1 (NPR1 homolog1)/OsNPR1 in rice results in enhanced resistance. While there are four rice NPR1 paralogs in the rice genome, none have been demonstrated to function in disease resistance. To study rice NPR1 paralog 3, we introduced constructs into rice and tested for effects on resistance to infection by Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial blight. While over‐expression of NH3 using the maize ubiquitin‐1 promoter failed to enhance resistance, introduction of an extra copy of NH3 driven by its own promoter (nNT‐NH3) resulted in clear, enhanced resistance. Progeny analysis confirms that the enhanced resistance phenotype, measured by Xoo‐induced lesion length, is associated with the NH3 transgene. Bacterial growth curve analysis indicates that bacterial population levels are reduced 10‐fold in nNT‐NH3 lines compared to control rice lines. The transgenic plants exhibit higher sensitivity to benzothiadiazole (BTH) and 2,6‐dichloroisonicotinic acid (INA) treatment as measured by increased cell death. Expression analysis of pathogenesis‐related (PR) genes showed that nNT‐NH3 plants display greatly enhanced induction of PR genes only after treatment with BTH. Our study demonstrates an alternative method to employ a regulatory protein to enhance plant defence. This approach avoids using undesirable constitutive, high‐level expression and may prove to be more practical for engineering resistance.     

Resistance and biomass in Arabidopsis: a new model for Salicylic Acid perception

Salicylic acid (SA) is an essential hormone for plant defence and development. SA perception is usually measured by counting the number of pathogens that grow in planta upon an exogenous application of the hormone. A biological SA perception model based on plant fresh weight reduction caused by disease resistance in Arabidopsis thaliana is proposed. This effect is more noticeable when a chemical analogue of SA is used, like Benzothiadiazole (BTH). By spraying BTH several times, a substantial difference in plant biomass is observed when compared with the mock treatment. Such difference is dose‐dependent and does not require pathogen inoculation. The model is robust and allows for the comparison of different Arabidopsis ecotypes, recombinant inbreed lines, and mutants. Our results show that two mutants, non‐expresser of pathogenesis‐related genes 1 (npr1) and auxin resistant 3 (axr3), fail to lose biomass when BTH is applied to them. Further experiments show that axr3 responds to SA and BTH in terms of defence induction. NPR1‐related genotypes also confirm the pivotal role of NPR1 in SA perception, and suggest an active program of depletion of resources in the infected tissues.