Pathogens and plants are in a constant battle with one another, the result of which is either the restriction of pathogen growth via constitutive or induced plant defense responses or the pathogen colonization of plant cells and tissues that cause disease. Elicitins are a group of highly conserved proteins produced by certain oomycete species, and their sterol binding ability is recognized as an important feature in sterol–auxotrophic oomycetes. Elicitins also orchestrate other aspects of the interactions of oomycetes with their plant hosts. The function of elicitins as avirulence or virulence factors is controversial and is dependent on the host species, and despite several decades of research, the function of these proteins remains elusive. We summarize here our current understanding of elicitins as either defense-promoting or defense-suppressing agents and propose that more recent approaches such as the use of ‘omics’ and gene editing can be used to unravel the role of elicitins in host–pathogen interactions. A better understanding of the role of elicitins is required and deciphering their role in host–pathogen interactions will expand the strategies that can be adopted to improve disease resistance and reduce crop losses.

Phytophthora cinnamomi is an oomycete plant pathogen with a host range of almost 5000 plant species worldwide and therefore poses a serious threat to biodiversity. Omics technology has provided significant progress in our understanding of oomycete biology, however, transformation studies of Phytophthora for gene functionalisation are still in their infancy. Only a limited number of Phytophthora species have been successfully transformed and gene edited to elucidate the role of particular genes. There is a need to escalate our efforts to understand molecular processes, gene regulation and infection mechanisms of the pathogen to enable us to develop new disease management strategies. The primary obstacle hindering the advancement of transformation studies in Phytophthora is their challenging and unique nature, coupled with our limited comprehension of why they remain such an intractable system to work with. In this study, we have identified some of the key factors associated with the recalcitrant nature of P. cinnamomi. We have incorporated fluorescence microscopy and flow cytometry along with the organelle-specific dyes, fluorescein diacetate, Hoechst 33342 and MitoTracker™ Red CMXRos, to assess P. cinnamomi-derived protoplast populations. This approach has also provided valuable insights into the broader cell biology of Phytophthora. Furthermore, we have optimized the crucial steps that allow transformation of P. cinnamomi and have generated transformed isolates that express a cyan fluorescent protein, with a transformation efficiency of 19.5%. We therefore provide a platform for these methodologies to be applied for the transformation of other Phytophthora species and pave the way for future gene functionalisation studies.

Phytophthora cinnamomi is a globally destructive pathogen causing disease in over 5000 plant species. As sterol auxotrophs, Phytophthora species rely on host-derived phytosterols for reproduction, yet the effects of pathogen infection on plant sterol biosynthesis remains unclear. We utilised a soil-free plant growth system to analyze the impacts of P. cinnamomi on Nicotiana benthamiana roots, a new model for studying P. cinnamomi–plant root interactions. Our results show that P. cinnamomi successfully infected all ecotypes tested, but infection was inhibited by the systemic chemical, phosphite. While phosphite is traditionally associated with the activation of plant defence mechanisms, we show that phosphite also modulates plant immune receptors and phytosterol biosynthesis. qPCR analyses revealed a two-fold upregulation of the N. benthamiana elicitin receptor, Responsive to Elicitins (REL), and its co-receptor, suppressor of BIR1-1 (SOBIR) during P. cinnamomi infection when compared with infected, phosphite-treated plants. Furthermore, key genes related to plant sterol biosynthesis were upregulated in their expression during pathogen infection but were suppressed in phosphite-treated and infected plants. Notably, the cytochrome P450 family 710 (CYP710A) gene encoding a C22-sterol desaturase, involved in stigmasterol production, a phytosterol known to be linked to plant susceptibility to pathogens, was downregulated in phosphite-treated plants, independent of infection status. These findings reveal novel insights into the role of phosphite in modulating plant immune responses and sterol metabolism, with potential in managing diseases caused by P. cinnamomi.

Graphical abstract showing activated carbon from municipal garden waste used in long-term column filtration of reservoir water, promoting biofilm formation and enhancing NOM removal, resulting in improved effluent quality across different carbon media. This is the first research to investigate the conversion potential of garden-waste-based activated carbon (SAC) into biological activated carbon (BAC) for water treatment. Five identical columns containing different carbon media were operated with reservoir water for eight months to compare the performance of natural organic matter (NOM) removal. Effluent chemistry was monitored regularly, and three distinct phases were observed across the operational period for all carbon media. From days 1 to ∼65, ∼65 to 146, and 146 onwards, phases can be defined as the development phase, the breakthrough phase, and the equilibrium phase, respectively. Conversion of activated carbon (AC) into BAC was demonstrated by the steady removal of dissolved organic carbon (DOC) during the equilibrium phase, biofilm formation on the AC media, and was visualized. Seeding with pre-established BAC did not enhance column stabilization time. Despite having lower initial DOC removal, SAC ultimately showed a similar removal efficiency (37.5%) to commercial AC by the end of the experiment, particularly for NOM with a molecular weight below 3,000 Da. Therefore, the results suggest SAC as an effective medium for biological filtration and this finding may open up a promising approach for water utilities to provide affordable services through the re-use of municipal garden waste.

Phytophthora cinnamomi is a major plant pathogen that affects economically important crops and natural ecosystems, posing a threat to global biodiversity. While gene editing has emerged as a powerful tool for functional genomics in various Phytophthora species, its application in P. cinnamomi remains underexplored. To address this gap, our study investigated the challenges of implementing CRISPR/Cas9-mediated gene editing in P. cinnamomi, with the insights gained applicable to other gene editing platforms. We designed guide RNAs (gRNAs) targeting β-cinnamomin, a highly basic elicitin expressed by the pathogen during early infection stages, known for its role in sterol recruitment. Using an “all-in-one” plasmid containing the gRNA, Cas9, and an antibiotic resistance gene as a selectable marker, we transformed P. cinnamomi protoplasts via PEG/CaCl₂-mediated methods. The successful integration of the nptII gene, which confers geneticin (G418) resistance, was confirmed in heterokaryotic regenerants. To isolate pure mutants and eliminate wild-type dominance, we derived homokaryotic colonies from nptII-positive transformants. Mutation screening was performed using mismatch detection assays, T7 endonuclease 1 (T7E1), and restriction fragment length polymorphism (RFLP), followed by Sanger sequencing. Despite the integration of the nptII gene, the β-cinnamomin sequence in the transformants remained identical to the wild-type sequence, indicating challenges in detecting and achieving targeted gene disruption. This study identifies critical steps for optimising mutagenesis in P. cinnamomi, highlighting the importance of thorough preliminary screening, effective separation of heterokaryotic populations, and the isolation of homokaryotic colonies.