Advances in Understanding Defense Mechanisms in Persea americana Against Phytophthora cinnamomi

Abstract

Avocado (Persea americana) is an economically important fruit crop world-wide, the production of which is challenged by notable root pathogens such as Phytophthora cinnamomi and Rosellinia necatrix. Arguably the most prevalent, P. cinnamomi, is a hemibiotrophic oomycete which causes Phytophthora root rot, leading to reduced yields and eventual tree death. Despite its’ importance, the development of molecular tools and resources have been historically limited, prohibiting significant progress toward understanding this important host-pathogen interaction. The development of a nested qPCR assay capable of quantifying P. cinnamomi during avocado infection has enabled us to distinguish avocado rootstocks as either resistant or tolerant - an important distinction when unraveling the defense response. This review will provide an overview of our current knowledge on the molecular defense pathways utilized in resistant avocado rootstock against P. cinnamomi. Notably, avocado demonstrates a biphasic phytohormone profile in response to P. cinnamomi infection which allows for the timely expression of pathogenesis-related genes via the NPR1 defense response pathway. Cell wall modification via callose deposition and lignification have also been implicated in the resistant response. Recent advances such as composite plant transformation, single nucleotide polymorphism (SNP) analyses as well as genomics and transcriptomics will complement existing molecular, histological, and biochemical assay studies and further elucidate avocado defense mechanisms.

Differing Responses to Phytophthora cinnamomi Infection in Susceptible and Partially Resistant Persea americana (Mill.) Rootstocks: A Case for the Role of Receptor-Like Kinases and Apoplastic Proteases

“…The molecular basis of P. cinnamomi resistance in avocado has been the topic of a recent discussion (van den Berg et al, 2021 ). This review provided an up-to-date justification and classification of avocado rootstocks as resistant, partially resistant, tolerant, or susceptible to P. cinnamomi .…”

“…In recent years, avocados have gained popularity because of their nutritional profile coupled with numerous health benefits associated with their consumption (Hurtado-Fernández et al, 2018 ). However, the production of avocado is severely threatened by the persistence of several pathogens in major avocado-growing regions of the world (van den Berg et al, 2021 ).…”

“…To augment the use of partially resistant rootstocks as a control measure for future management of PhRR, a comprehensive understanding of the P. americana-P. cinnamomi interaction is essential (van den Berg et al, 2021 ). One way of understanding host-pathogen interactions is quantifying gene expression in both the pathogen and the host during infection.…”

Warming Scenarios and Phytophthora cinnamomi Infection in Chestnut (Castanea sativa Mill.)

“…Phenolic compounds also participate in the lignification of cell walls, an additional defensive response to pathogens [ 37 ]. Lignin enrichment of root cell walls has been reported as a plant-defensive response in the early stages (hours) after infection, although, in susceptible plants, it is not sufficient to stop pathogen hyphae from penetrating into the roots [ 70 , 71 ]. It has been reported that coniferyl aldehyde is used by plants for the hydroxylation of the enzyme ferulate-5-hydroxylase as a downstream substrate in the lignin pathway [ 72 , 73 ].…”

Differences in the Proteomic and Metabolomic Response of Quercus suber and Quercus variabilis During the Early Stages of Phytophthora cinnamomi Infection

“…Phytophthora cinnamomi is one of the most aggressive tree pathogens in the world, and as such it is usually able to penetrate and colonize the roots of more than 5,000 host plant species, regardless of their level of susceptibility ( Shearer et al, 2007 ; Allardyce et al, 2012 ; Hardham and Blackman, 2018 ; Camisón et al, 2019 ). Plant defense response in tolerant tree species tends to be based on stopping the progress of the pathogen within the host’s tissues and/or replacing the dead roots fast enough ( Moreira and Martins, 2005 ; van den Berg et al, 2021 ). In agreement with these reports, within 36 hpi, the roots of both Q. suber and Q. variabilis developed necrotic tissue ( Figure 1C ).…”