Effector proteins play important roles in the infection by pathogenic oomycetes and fungi or the colonization by endophytic and mycorrhizal fungi. They are either translocated into the host plant cells via specific translocation mechanisms and function in the host's cytoplasm or nucleus, or they reside in the apoplast of the plant cells and act at the extracellular host-microbe interface. Many effector proteins possess conserved motifs (such as the RXLR, CRN, LysM, RGD, DELD, EAR, RYWT, Y/F/WXC or CFEM motifs) localized in their N-or C-terminal regions. Analysis of the functions of effector proteins, especially so-called "core effectors", is crucial for the understanding of pathogenicity/symbiosis mechanisms and plant defense strategies, and helps to develop breeding strategies for pathogen-resistant cultivars, and to increase crop yield and quality as well as abiotic stress resistance. This review summarizes current knowledge about these effector proteins with the conversed motifs and their involvement in pathogenic or mutualistic plant/fungal interactions.
Studies on population genetics of Villosiclava virens are limited because of the lack of polymorphic markers. Based on a draft genome sequence of isolate HWD‐2 produced in this study, 20 of 403 potential simple sequence repeats (SSR) loci showed polymorphisms in preliminary screening using eight diverse V. virens isolates. Among polymorphic loci, most of them with tetra‐ to hexanucleotide unit motifs showed higher levels of polymorphism than loci with smaller motifs. After testing with 20 polymorphic SSR markers, the 87 isolates of V. virens from eight populations in China showed a high level of genetic diversity, with each as a unique haplotype. This differs from some previous findings showing little to no genetic variation based on random amplified polymorphic DNA and amplified fragment length polymorphism analyses. Among eight populations from major rice production areas of China, the population from Guangxi province in south China showed the highest levels of polymorphism, which led to the speculation that it might be closer to the centre of origin of this pathogen. The northern, central and eastern populations (Jilin, Liaoning, Hubei, Hunan, Jiangxi and Zhejiang), when considered together as a group, showed significant molecular variation compared to the southern populations (Fujian and Guangxi) (ΦPT = 0·043, P = 0·037). A significant relationship (Mantel test, P = 0·027) but with low correlation (R2 = 0·23) was also found between geographic distance and genetic distance. The 20 polymorphic SSR primer pairs designed in this study provide a tool for further research on the population diversity of this emerging fungal pathogen of rice.
Ustilaginoidea virens is a fungal pathogen that causes the false smut disease in rice and reduces the yield and quantity of the grains. A nested polymerase chain reaction (PCR)-based assay was developed to detect U. virens using genes of U. virens as specific targets. Ninety-six candidate genes of U. virens were found through first-round homology screening against a local database comprising 46 genomes of fungi, bacteria, and plants, with a second-round comparison with the GenBank NR database to further identify genes unique to U. virens. Among 96 remaining candidate genes, 20 of them (GenBank accessions KY617806 to KY617825) were randomly selected for further testing and, eventually, six sets of nested PCR primers were developed after further sensitivity, specificity, and detection tests. All six sets could detect DNA of U. virens at as little as 1 to 10 fg/μl from field or lab samples. These primers may be used to detect infection by U. virens at early stages, for use in research toward mitigating disease spread, as well as for studying the ecology of U. virens. This study also serves to illustrate that a comparative genomics method may allow for selection and development of highly specific primers once draft or complete genomes are available.
Gene expression analysis largely improves our understanding of the molecular basis underpinning various plant biological processes. Stable reference genes play a foundational role during the normalization of gene expression levels. However, until now, there have been few reference genes suitable for ginger reverse transcription-quantitative PCR (RT-qPCR) research. In this study, 29 candidate reference genes with stable expression patterns across multiple ginger tissues and 13 commonly used reference genes were selected to design RT-qPCR primers. After amplification specificity validation, 32 candidates were selected and further evaluated by RT-qPCR using samples from various organs subjected to NaCl, drought, heat, waterlogging, and chilling stress. Four strategies, including delta-CT, BestKeeper, geNorm, and NormFinder, were used to rank the stability of reference genes, and the ranks produced by these four strategies were comprehensively evaluated by RefFinder to determine the final rank. Overall, the top three stability reference genes indicated by RefFinder were RBP > ATPase > 40S_S3. Their expression pattern correlation analysis showed that the coefficients among each pair of RBP, ATPase, and 40S_S3 were larger than 0.96, revealing consistent and stable expression patterns under various treatments. Then, the expression of three pathogenesis-related (PR) genes and seven MYB genes in rhizomes during postharvest storage and subjected to pathogen infection was normalized by RBP, ATPase, 40S_S3, RBP and ATPase, ATPase and 40S-S3, and RBP and 40S-S3. The results showed that PR and MYB genes were induced by postharvest deterioration and pathogen infection. The correlation coefficients of RBP/ATPase, RBP/40S_S3, ATPase/40S_S3, RBP and ATPase/ATPase and 40S-S3, RBP and ATPase/RBP and 40S-S3, and ATPase and 40S-S3/RBP and 40S-S3 were 0.99, 0.96, 0.99, 0.99, 1.00, and 1.00, respectively, which confirmed the stability of these three reference genes in postharvest biology studies of ginger. In summary, this study identified appropriate reference genes for RT-qPCR in ginger and facilitated gene expression studies under biotic and abiotic stress conditions.
Silica nanoparticles (SiNPs) offer an ecofriendly and environmentally safe alternative for plant disease management. However, the mechanisms of SiNPs-induced disease resistance are largely unknown. This research evaluated the application of SiNPs in controlling the postharvest decay of ginger rhizomes inoculated with Fusarium solani. In vitro study showed that SiNP had little inhibitory effect on mycelial growth and spore germination of F. solani and did not significantly change mycelium’s MDA content and SDH activity. In vivo analysis indicated that SiNPs decreased the degree of decay around the wounds and decreased the accumulation of H2O2 after long-term pathogenic infection through potentiating the activities of antioxidant enzymes such as SOD, APX, PPO, and CAT. SiNP150 increased the CHI, PAL, and GLU activity at the onset of the experiment. Moreover, SiNP150 treatment increased total phenolics contents by 1.3, 1.5, and 1.2-times after 3, 5, and 7 days of treatment, and increased total flavonoids content throughout the experiment by 9.3%, 62.4%, 26.9%, 12.8%, and 60.8%, respectively. Furthermore, the expression of selected phenylpropanoid pathway-related genes was generally enhanced by SiNPs when subjected to F. solani inoculation. Together, SiNPs can effectively reduce the fungal disease of ginger rhizome through both physical and biochemical defense mechanisms.
Botanical pesticides have gradually become accepted for use in the control of agricultural pests. In order to clarify the active compounds of the ginger (Zingiber officinale) shoot extract (GSE) and its inhibitory effect on the growth of sorghum aphids (Melanaphis sorghi). In this study, LC-MS/MS was used to determine the major active compounds of the GSE, and leaf disc method was used to explore the insecticidal effect of the active compounds of ginger on sorghum aphids and the response mechanism of sorghum aphids. The results showed that phenolic acids were identified as the main active compounds, followed by flavonoids. The aphidicidal activity test using the above compounds found that 6-gingerol, and quercetin-3-O-rutinoside exhibited aphidicidal activity (GSE > quercetin-3-O-rutinoside > 6-gingerol). The growth of sorghum aphid was evaluated by using different concentrations of the GSE. It was found that with the increase of concentration and treatment time, the litter size, longevity and molting of aphids significantly decreased, and the mortality of aphids increased. The enzyme activity of aphids treated with 15 mg·mL−1 GSE was determined, and it was found that the GSE could significantly inhibit the activities of pepsin, lipase and α-amylase of aphids, while the activity of superoxide dismutase (SOD) was significantly activated. The activities of peroxidase (POD) and catalase (CAT) increased at first and then decreased. In detoxification enzymes, the carboxylesterase (CarE) activity was significantly activated, the acetylcholinesterase (AChE) activity was significantly inhibited, and the glutathione S-transferase (GST) activity increased at first and then decreased. The above results indicated that the GSE may become a botanical pesticide for aphid control and provide new resources for the development of aphid biological agents.
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