Search Results (5)

Strawberry fruit is highly appreciated worldwide for its organoleptic and healthy properties. However, this plant is attacked by many pathogenic fungi, which significantly affect fruit production and quality at pre- and post-harvest stages, making chemical applications the most effective but undesirable strategy to control diseases that has been found so far. Alternatively, genetic manipulation, employing plant key genes involved in defense, such as members of the NPR-like gene family, has been successful in many crops to improve resistance. The identification and use of the endogenous counterpart genes in the plant of interest (as it is the case of strawberry) is desirable as it would increase the favorable outcome and requires prior knowledge of their defense-related function. Using RNAi technology in strawberry, transient silencing of Fragaria ananassa NPR3 members in fruit significantly reduced tissue damage after Colletotrichum acutatum infection, whereas the ectopic expression of either FaNPR3.1 or FaNPR3.2 did not have an apparent effect. Furthermore, the ectopic expression of FaNPR3.2 in Arabidopsis thaliana double-mutant npr3npr4 reverted the disease resistance phenotype to Pseudomonas syringe to wild-type levels. Therefore, the results revealed that members of the strawberry FaNPR3 clade negatively regulate the defense response to pathogens, as do their Arabidopsis AtNPR3/AtNPR4 orthologs. Also, evidence was found showing that FaNPR3 members act in strawberry (F. ananassa) as positive regulators of WRKY genes, FaWRKY19 and FaWRKY24; additionally, in Arabidopsis, FaNPR3.2 negatively regulates its orthologous genes AtNPR3/AtNPR4. We report for the first time the functional characterization of FaNPR3 members in F. ananassa, which provides a relevant molecular basis for the improvement of resistance in this species through new breeding technologies. Full article

The salicylic acid receptor NPR1 (nonexpressor of pathogenesis-related genes) and its paralogues NPR3 and NPR4 are master regulators of plant immunity. Commercial strawberry (Fragaria × ananassa) is a highly valued crop vulnerable to various pathogens. Historic confusions regarding the identity of NPR-like genes have hindered research in strawberry resistance. In this study, the comprehensive identification and phylogenic analysis unraveled this family, harboring 6, 6, 5, and 23 members in F. vesca, F. viridis, F. iinumae, and F. × ananassa, respectively. These genes were clustered into three clades, with each diploid member matching three to five homoalleles in F. × ananassa. Despite the high conservation in terms of gene structure, protein module, and functional residues/motifs/domains, substantial divergence was observed, hinting strawberry NPR proteins probably function in ways somewhat different from Arabidopsis. RT-PCR and RNAseq analysis evidenced the transcriptional responses of FveNPR1 and FxaNPR1a to Colletotrichum fructicola. Extended expression analysis for strawberry NPR-likes helped to us understand how strawberry orchestrate the NPRs-centered defense system against C. fructicola. The cThe current work supports that FveNPR1 and FxaNPR1a, as well as FveNPR31 and FxaNPR31a-c, were putative functional orthologues of AtNPR1 and AtNPR3/4, respectively. These findings set a solid basis for the molecular dissection of biological functions of strawberry NPR-like genes for improving disease resistance. Full article

Proteins with conserved SET domain play a critical role in plant immunity. However, the means of organization and functions of these proteins are unclear, particularly in non-model plants such as pepper (Capsicum annum L.). Herein, we functionally characterized CaASHH3, a member of class II (the ASH1 homologs H3K36) proteins in pepper immunity against Ralstonia solanacearum and Pseudomonas syringae pv tomato DC3000 (Pst DC3000). The CaASHH3 was localized in the nucleus, and its transcript levels were significantly enhanced by R. solanacearum inoculation (RSI) and exogenous application of salicylic acid (SA), methyl jasmonate (MeJA), ethephon (ETH), and abscisic acid (ABA). Knockdown of CaASHH3 by virus-induced gene silencing (VIGS) compromised peppers’ resistance to RSI. Furthermore, silencing of CaASHH3 impaired hypersensitive-response (HR)-like cell death response due to RSI and downregulated defense-associated marker genes, including CaPR1, CaNPR1, and CaABR1. The CaASHH3 protein was revealed to affect the promoters of CaNPR1, CaPR1, and CaHSP24. Transiently over-expression of CaASHH3 in pepper leaves elicited HR-like cell death and upregulated immunity-related marker genes. To further study the role of CaASHH3 in plant defense in vivo, CaASHH3 transgenic plants were generated in Arabidopsis. Overexpression of CaASHH3 in transgenic Arabidopsis thaliana enhanced innate immunity against Pst DC3000. Furthermore, CaASHH3 over-expressing transgenic A. thaliana plants exhibited upregulated transcriptional levels of immunity-associated marker genes, such as AtNPR1, AtPR1, and AtPR2. These results collectively confirm the role of CaASHH3 as a positive regulator of plant cell death and pepper immunity against bacterial pathogens, which is regulated by signaling synergistically mediated by SA, JA, ET, and ABA. Full article

Squamosa promoter binding protein (SBP)-box genes are plant-specific transcription factors involved in plant growth and development, morphogenesis and biotic and abiotic stress responses. However, these genes have been understudied in pepper, especially with respect to defense responses to Phytophthora capsici infection. CaSBP11 is a SBP-box family gene in pepper that was identified in our previous research. Silencing CaSBP11 enhanced the defense response of pepper plants to Phytophthora capsici. Without treatment, the expression of defense-related genes (CaBPR1, CaPO1, CaSAR8.2 and CaDEF1) increased in CaSBP11-silenced plants. However, the expression levels of these genes were inhibited under transient CaSBP11 expression. CaSBP11 overexpression in transgenic Nicotiana benthamiana decreased defense responses, while in Arabidopsis, it induced or inhibited the expression of genes in the salicylic acid and jasmonic acid signaling pathways. CaSBP11 overexpression in sid2-2 mutants induced AtNPR1, AtNPR3, AtNPR4, AtPAD4, AtEDS1, AtEDS5, AtMPK4 and AtNDR1 expression, while AtSARD1 and AtTGA6 expression was inhibited. CaSBP11 overexpression in coi1-21 and coi1-22 mutants, respectively, inhibited AtPDF1.2 expression and induced AtPR1 expression. These results indicate CaSBP11 has a negative regulatory effect on defense responses to Phytophthora capsici. Moreover, it may participate in the defense response of pepper to Phytophthora capsici by regulating defense-related genes and the salicylic and jasmonic acid-mediated disease resistance signaling pathways. Full article

Huanglongbing (HLB), a bacterial disease caused by Candidatus Liberibacter asiaticus (CLas), is a major threat to the citrus industry. In a previous study conducted by our laboratory, several citrus transgenic trees expressing the Arabidopsis thaliana NPR1 (AtNPR1) gene remained HLB-free when grown in a field site under high HLB disease pressure. To determine the molecular mechanisms behind AtNPR1-mediated tolerance to HLB, a transcriptome analysis was performed using AtNPR1 overexpressing transgenic trees and non-transgenic trees as control, from which we identified 57 differentially expressed genes (DEGs). Data mining revealed the enhanced transcription of genes encoding pathogen-associated molecular patterns (PAMPs), transcription factors, leucine-rich repeat receptor kinases (LRR-RKs), and putative ankyrin repeat-containing proteins. These proteins were highly upregulated in the AtNPR1 transgenic line compared to the control plant. Furthermore, analysis of protein–protein interactions indicated that AtNPR1 interacts with CsNPR3 and CsTGA5 in the nucleus. Our results suggest that AtNPR1 positively regulates the innate defense mechanisms in citrus thereby boosting resistance and effectively protecting the plant against HLB. Full article