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Multiprotein bridging factor 1 (MBF1) is a transcription coactivator that has a general defense response to pathogens. However, the regulatory mechanisms of MBF1 resistance bacterial wilt remain largely unknown. Here, the role of StMBF1c in potato resistance to Ralstonia solanacearum infection was characterized. qRT-PCR assays indicated that StMBF1c could was elicited by SA, MJ and ABA and the time-course expression pattern of the StMBF1c gene induced by R. solanacearum was found to be twice significant upregulated expression during the early and middle stages of bacterial wilt. Combined with the co-expression analysis of disease-resistant marker genes, gain-of-function and loss-of-function assays demonstrated that StMBF1c was associated with defence priming. Overexpression or silencing the MBF1c could enhance plants resistance or sensitivity to R. solanacearum through inducing or reducing NPR and PR genes related to SA signal pathway. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) experiment results confirmed the interaction of StMBF1c with StTPS5 which played a key role in ABA signal pathway in potato. It is speculated that by combining StTPS5 and resistance marker genes, StMBF1c is activated twice to participate in potato bacterial wilt resistance, in which EPI, PTI involved., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Bacterial wilt (BW) is a serious disease that affects potato (Solanum tuberosum L.) production. Although resistance to this disease has been reported, the underlying mechanism is unknown. In this study, we identified a NAC family transcription factor (StNACb4) from potato and characterised its structure, function, expression, its localisation at the tissue and its role in BW resistance. To this end, the transgenic Nicotiana benthamiana Domin lines were generated in which the expression of NACb4 was constitutively upregulated or suppressed using RNAi. Different tobacco mutants were stained after inoculating with Ralstonia solanacearum to observe the cell death and callose deposition. The results indicated that StNACb4 could be upregulated under the induction of R. solanacearum, and salicylic acid, abscisic acid and methyl jasmonate could also induce the expression of StNACb4. Tissue localisation analysis indicated that its expression was tissue specific, and it was mainly in the phloem of the vascular system of stems and leaves. NbNACb4 gene silencing can enhance the sensitivity of tobacco to R. solanacearum; on the contrary, StNACb4 gene overexpression can enhance the tolerance of tobacco to R. solanacearum. Meanwhile, StNACb4 gene overexpression can induce cell death and callose deposition in tobacco. The upregulated expression of StNACb4 can also activate the StPR10 gene expression. Our results provide important new insights into the regulatory mechanisms of bacterial wilt resistance in potato.

Although nonspecific lipid transfer proteins (nsLTPs) are widely expressed during plant defence responses to pathogens, their functions and regulation are not fully understood. In this article, we report the isolation of a cDNA for the new nsLTP, StLTPa7, from cultivated potato (Solanum tuberosum) infected with Ralstonia solanacearum. The cDNA was predicted to encode a type 1 nsLTP containing an N-terminal signal sequence and possessing the characteristic features of nsLTPs. A phylogenetic analysis showed that the encoded amino acid sequence of the nsLTP was similar to those of other previously reported plant nsLTPs, which contain a putative calmodulin-binding site consisting of approximately 12 highly conserved amino acid residues. The expression of the StLTPa7 gene was studied during the early stages of potato-R. solanacearum interaction using real-time quantitative polymerase chain reaction (qRT-PCR) and Northern analyses, and a complex calcium (Ca2+)-associated pattern of expression was observed with the following features: (i) transcripts of the StLTPa7 gene were systemically up-regulated by infection with R. solanacearum; (ii) the StLTPa7 gene was stimulated by salicylic acid, methyl jasmonate, abscisic acid and Ca2+; (iii) qRT-PCR showed that, during the early stage of R. solanacearum infection, nsLTP transcripts accumulated over a time course that paralleled that of Ca2+ accumulation, detected using environmental scanning electron microscopy and energy-dispersive X-ray (EDAX) spectrometry; and (iv) the Ca2+ channel blocker, ruthenium red, partially blocked R. solanacearum-induced StLTPa7 expression. This report represents the first use of EDAX analysis to establish a synchrony between Ca2+ accumulation and nsLTP expression in response to potato-R. solanacearum interactions. Collectively, these results suggest that StLTPa7 may be a pathogen- and Ca(2+)-responsive plant defence gene.

Cell wall glycine‐rich proteins (GRPs) play important roles in plant growth and development, as well as in the effective prevention of plant diseases. Although members of the GRP family have been identified in several plants, a comprehensive analysis of GRPs has not been reported in Solanaceae plants. In this study, 43 GRPs were identified from Solanum tuberosum (named StGRPs), Solanum lycopersicum, Capsicum annuum and Nicotiana attenuata. The comparative study of these GRPs showed that they were conservative in physical properties, structures of genes and motifs. The expression patterns of Solanum tuberosum StGRPs under biotic and abiotic stress were analysed and presented very diverse profiles in responding to ABA, IAA, GA3, high salinity, pathogen and heat stress. Some StGRPs were preferentially and specifically expressed during the development of petioles and tubers, in which the expression of StGRPs was more sensitive to ABA confirmed by qRT‐PCR analysis. The strongly up‐regulated expression of StGRP1 induced by Ralstonia solanacearum indicated the positive role involved in the resistance against the bacterial wilt pathogen. Tissue localization analyses by Digoxin/fluorescence in situ hybridization indicated that the expression of StGRP1 was vascular‐specific and associated with cell wall thickening in vascular bundles and interfascicular fibres after R. solanacearum inoculation. These findings may provide a new insight into the roles of GRPs in adaptation to diverse stresses and in resistance to R. solanacearum in potatoes. [ABSTRACT FROM AUTHOR]

Abstract: Plant root secretion can be regarded as signal molecules, which exerts impact on microorganisms in the rhizosphere ecological niche. We obtained gene expression profile of Ralstonia solanacearumPO41 under the root secretions environment of Solanum tuberosum at the time points of 8 hrs, 16 hrs and 24 hrs, respectively, after infection with RNA microarray technology. Bioinformatics tools of differential genes expression analysis, GO functional analysis, cluster analysis and pathway analysis were conducted to find out the pathogenic genes and other related genes. We found that the virulence factors of R. solanacearum mainly focused on the output pathways of toxic protein (Sec pathway, Tat pathway and type III secretion system (T3SS)), the aggregation and transfer of exopolysaccharides and the chemotactic movement and adhesion of flagellum in the potato root secretion ecological niche, while the virulence factors in the atypical output pathway mainly distributed in Sec (secB, secDF, yidc) and Tat (tatA, tatC) pathways to promote the output of folded and unfolded toxic proteins. The fliIATPase was obviously upregulated 8 hrs postinoculation, suggesting that type III secretion system was only active at the early stage of PO41 infection. The upregulated expression of phosphoglucomutase and epimerase showed that the virulence factor of exopolysaccharides (EPS) was synthesized at the early stage of R. solanacearum infection. Chemotactic receptor and motor protein were obviously upregulated within 24 hrs postinoculation. Our study revealed that R. solanacearumPO41 had already colonized to the roots within 24 hrs with the stimulating of root secretion. Some pathogenic genes were upregulated during this period. [ABSTRACT FROM AUTHOR]