Molecular characterisation of the broad-spectrum resistance to powdery mildew conferred by the Stpk-V gene from the wild species Haynaldia villosa

Phylogenetic Analysis of Wall-Associated Kinase Genes in Triticum Species and Characterization of TaWAK7 Involved in Wheat Powdery Mildew Resistance

Wall-associated kinases (WAKs), a group of receptor-like kinases, have been found to play important roles in defending against pathogens and in various developmental processes. However, the importance of this family in wheat remains largely unknown. Wheat powdery mildew is caused by Blumeria graminis f. sp. tritici (Bgt), which initiates infection on the cell surface and forms haustoria inside the cell; therefore, the defense to Bgt involves extracellular and subsequently intracellular signals. In this study, WAKs were identified genome-wide and analyzed phylogenetically, and then a transmembrane WAK gene that putatively participated in pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity to Bgt was functionally and evolutionarily investigated. In total, 1,193 WAKs were identified from wheat and its Gramineae relatives. Phylogenetic analysis indicated that WAKs expanded through tandem duplication or segment duplication. TaWAK7, from chromosome 2A, was identified as a Bgt-inducible gene both in susceptible and resistant materials, but it showed distinct responsive patterns. Functional analysis showed that TaWAK7 was involved in both the basal and resistance gene-mediated resistances. The specific gene structures and protein characteristics of TaWAK7, along with its orthologs, were characterized both in subgenomes of Triticum spp. and in the A genome of multiple wheat accessions, which revealed that TaWAK7 orthologs underwent complex evolution with frequent gene fusion and domain deletion. In addition, three cytoplasmic proteins interacting with TaWAK7 were indicated by yeast two-hybrid and bimolecular fluorescence complementation assays. Binding of TaWAK7 with these proteins could change its subcellular localization from the plasma membrane to the cytoplasm. This study provides a better understanding of the evolution of WAKs at the genomic level and TaWAK7 at the gene level and provides useful clues for further investigation of how WAKs transmit the extracellular signals to the cytoplasm to activate defense responses.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

NAC Transcription Factors as Positive or Negative Regulators during Ongoing Battle between Pathogens and Our Food Crops

The NAC (NAM, ATAF1/2, and CUC2) family of proteins is one of the largest plant-specific transcription factor (TF) families and its members play varied roles in plant growth, development, and stress responses. In recent years, NAC TFs have been demonstrated to participate in crop-pathogen interactions, as positive or negative regulators of the downstream defense-related genes. NAC TFs link signaling pathways between plant hormones, including salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA), or other signals, such as reactive oxygen species (ROS), to regulate the resistance against pathogens. Remarkably, NAC TFs can also contribute to hypersensitive response and stomatal immunity or can be hijacked as virulence targets of pathogen effectors. Here, we review recent progress in understanding the structure, biological functions and signaling networks of NAC TFs in response to pathogens in several main food crops, such as rice, wheat, barley, and tomato, and explore the directions needed to further elucidate the function and mechanisms of these key signaling molecules.

Evaluating responses of nitrification and denitrification to the co-selective pressure of divalent zinc and tetracycline based on resistance genes changes

The responses of nitrification and denitrification to the divalent zinc (Zn(II)) and tetracycline (TC) co-selective pressure were evaluated in a sequencing batch reactor (SBR). The removal rates of organics and nitrogen, nitrifying and denitrifying enzymatic activity, and microbial diversity and richness at the Zn(II) and TC co-selective pressure were higher than those at the alone Zn(II) selective pressure, while were lower than those at the individual TC selective pressure. The Zn(II) and TC co-selective pressure induced the TC resistance genes abundance increase and the Zn(II) resistance genes levels decrease, and enhanced bacterial enzymatic modification resistance to TC and bacterial outer membrane resistance to Zn(II). The network analysis showed that the genera Nitrospira and Nitrosomonas of nitrifiers and the genera Ferruginibacter, Dechloromonas, Acidovorax, Rhodobacter, Thauera, Cloacibacterium, Zoogloea and Flavobacterium of denitrifiers were the potential hosts of antibiotics resistance genes (ARGs) and/or heavy metals resistance genes (HMRGs).

Exploiting Broad-Spectrum Disease Resistance in Crops: From Molecular Dissection to Breeding

Plant diseases reduce crop yields and threaten global food security, making the selection of disease-resistant cultivars a major goal of crop breeding. Broad-spectrum resistance (BSR) is a desirable trait because it confers resistance against more than one pathogen species or against the majority of races or strains of the same pathogen. Many BSR genes have been cloned in plants and have been found to encode pattern recognition receptors, nucleotide-binding and leucine-rich repeat receptors, and defense-signaling and pathogenesis-related proteins. In addition, the BSR genes that underlie quantitative trait loci, loss of susceptibility and nonhost resistance have been characterized. Here, we comprehensively review the advances made in the identification and characterization of BSR genes in various species and examine their application in crop breeding. We also discuss the challenges and their solutions for the use of BSR genes in the breeding of disease-resistant crops.

TaNAC6s are involved in the basal and broad-spectrum resistance to powdery mildew in wheat

NACs are important transcriptional factors involved in growth and development as well as responses to abiotic and biotic stresses in plants. In this study, TaNAC6 was identified as a differentially expressed gene between two lines with broad-spectrum resistance to powdery mildew, NAU9918 and OE_Stpk-V, and their corresponding susceptible isogenic lines, SM-1 and Yangmai158, after Bgt inoculation by transcriptome analysis. Then, three homoeologous genes of TaNAC6 were cloned and named as TaNAC6-A, TaNAC6-B and TaNAC6-D, respectively. Each member of TaNAC6s was subcellular localized to the nucleus and displayed the transcriptional activation activity. However, the responses of them to pathogens and phytohormones were different. Transient overexpression of each TaNAC6 reduced the haustorium index of Yangmai158, and stable transformation of TaNAC6-A enhanced its resistance against Bgt, implying that TaNAC6s play important roles in basal resistance. Silencing of TaNAC6s compromised the resistance of OE_Stpk-V and NAU9918 suggesting that TaNAC6s play positive roles in the broad-spectrum resistance against Bgt. TaNAC6s might be induced by JA and then feedback regulate the JA pathway leading to improved resistance to Bgt. The role of TaNAC6s and their orthologous genes HvNAC6 and ATAF1 in the powdery mildew resistance implied these NAC6 genes share a common signal pathway across species.