Molecular evidence of the avocado defense response to Fusarium kuroshium infection: a deep transcriptome analysis using RNA-Seq

Abstract

Fusarium kuroshium is a novel member of the Ambrosia Fusarium Clade (AFC) that has been recognized as one of the symbionts of the invasive Kuroshio shot hole borer, an Asian ambrosia beetle. This complex is considered the causal agent of Fusarium dieback, a disease that has severely threatened natural forests, landscape trees, and avocado orchards in the last 8 years. Despite the interest in this species, the molecular responses of both the host and F. kuroshium during the infection process and disease establishment remain unknown. In this work, we established an in vitro pathosystem using Hass avocado stems inoculated with F. kuroshium to investigate differential gene expression at 1, 4, 7 and 14 days post-inoculation. RNA-seq technology allowed us to obtain data from both the plant and the fungus, and the sequences obtained from both organisms were analyzed independently. The pathosystem established was able to mimic Fusarium dieback symptoms, such as carbohydrate exudation, necrosis, and vascular tissue discoloration. The results provide interesting evidence regarding the genes that may play roles in the avocado defense response to Fusarium dieback disease. The avocado data set comprised a coding sequence collection of 51,379 UniGenes, from which 2,403 (4.67%) were identified as differentially expressed. The global expression analysis showed that F. kuroshium responsive UniGenes can be clustered into six groups according to their expression profiles. The biologically relevant functional categories that were identified included photosynthesis as well as responses to stress, hormones, abscisic acid, and water deprivation. Additionally, processes such as oxidation-reduction, organization and biogenesis of the cell wall and polysaccharide metabolism were detected. Moreover, we identified orthologues of nucleotide-binding leucine-rich receptors, and their possible action mode was analyzed. In F. kuroshium, we identified 57 differentially expressed genes. Interestingly, the alcohol metabolic process biological category had the highest number of upregulated genes, and the enzyme group in this category may play an important role in the mechanisms of secondary metabolite detoxification. Hydrolytic enzymes, such as endoglucanases and a pectate lyase, were also identified, as well as some proteases. In conclusion, our research was conducted mainly to explain how the vascular tissue of a recognized host of the ambrosia complex responds during F. kuroshium infection since Fusarium dieback is an ambrosia beetle-vectored disease and many variables facilitate its establishment.

Partially Resistant Avocado Rootstock Dusa® Shows Prolonged Upregulation of Nucleotide Binding-Leucine Rich Repeat Genes in Response to Phytophthora cinnamomi Infection

“…BLASTp analysis was performed on the entire set of P. americana protein sequences and no additional PaNLR sequences could be identified. Furthermore, an independent study found only one TNL gene being expressed in Hass avocado stems during F. kuroshium infection ( Pérez-Torres et al, 2021 ). This validated that no TNL motifs were missed during PaNLR identification using the RGAugury program and WI genome.…”

“…To date, 49 complete putative NLR genes have been identified in avocado using microarray and RNA-sequencing analysis ( Van den Berg et al, 2018 ; Pérez-Torres et al, 2021 ). In the study done by Pérez-Torres et al (2021) , Hass avocado stems were infected with Fusarium kuroshium , which causes Fusarium dieback disease in avocado. However, only four NLR genes were differentially expressed after F. kuroshium infection.…”

Pathogenesis-related protein 10 in resistance to biotic stress: progress in elucidating functions, regulation and modes of action

“…A PR-10 of the MLP (major latex protein) type was also identified, negatively regulating plant defense, and two other MLPs that were repressed in plants subjected to biotic stressors ( Wang et al., 2017 ; He et al., 2020 ; Pérez-Torres et al., 2021 ). Two fungal pathogens inhibited MLP expression.…”

A successful defense of the narrow-leafed lupin against anthracnose involves quick and orchestrated reprogramming of oxidation–reduction, photosynthesis and pathogenesis-related genes

“…Significant downregulation of an MLP-like 423 gene was observed during avocado defense response to Fusarium kuroshium infection as well as during apple infections with Botryosphaeria berengeriana f. sp. piricola and Alternaria alternata apple pathotype 58 , 59 . Moreover, apple calli overexpressing an MLP-like 423 gene had lower expression of resistance-related genes, and were more sensitive to fungal infections 59 .…”