Transposable elements (TEs) are a dominant feature of most flowering plant genomes. Together with other accepted facilitators of evolution, accumulating data indicate that TEs can explain much about their rapid evolution and diversification. Genome size in angiosperms is highly correlated with TE content and the overwhelming bulk (>80%) of large genomes can be composed of TEs. Among retro-TEs, long terminal repeats (LTRs) are abundant, whereas DNA-TEs, which are often less abundant than retro-TEs, are more active. Much adaptive or evolutionary potential in angiosperms is due to the activity of TEs (active TE-Thrust), resulting in an extraordinary array of genetic changes, including gene modifications, duplications, altered expression patterns, and exaptation to create novel genes, with occasional gene disruption. TEs implicated in the earliest origins of the angiosperms include the exapted Mustang, Sleeper, and Fhy3/Far1 gene families. Passive TE-Thrust can create a high degree of adaptive or evolutionary potential by engendering ectopic recombination events resulting in deletions, duplications, and karyotypic changes. TE activity can also alter epigenetic patterning, including that governing endosperm development, thus promoting reproductive isolation. Continuing evolution of long-lived resprouter angiosperms, together with genetic variation in their multiple meristems, indicates that TEs can facilitate somatic evolution in addition to germ line evolution. Critical to their success, angiosperms have a high frequency of polyploidy and hybridization, with resultant increased TE activity and introgression, and beneficial gene duplication. Together with traditional explanations, the enhanced genomic plasticity facilitated by TE-Thrust, suggests a more complete and satisfactory explanation for Darwin’s “abominable mystery”: the spectacular success of the angiosperms.

This paper describes the effect of phosphite (Phi), a systemic chemical, on the induction of defence responses in Phytophthora cinnamomi-infected Arabidopsis thaliana accessions Ler and Col-0. Application of Phi to non-inoculated A. thaliana seedlings of accession Ler elevated transcription of defence genes in the salicylic acid (PR1 and PR5) and jasmonic acid ⁄ ethylene (THI2.1 and PDF1.2) pathways. Furthermore, a systemic increase in the expression of the PR1 gene was demonstrated in Phi-treated seedlings using the transgenic line PR1::GUS in the presence ⁄ absence of the pathogen by 72 h after inoculation. The cells of Phi-treated A. thaliana Ler leaves responded to P. cinnamomi zoospore inoculation with a rapid increase in callose deposition and hydrogen peroxide (H 2 O 2 ) production. Phi treatment resulted in the production of callose papillae 6 h earlier than in non-Phi-treated inoculated seedlings and enhanced the production of H 2 O 2 in the leaves of A. thaliana at the site of hyphal penetration and in cells away from the inoculation point. By 24 h after infection, clear differences in the amount of H 2 O 2 production were observed between the Phi-treated and non-Phi-treated plants. These rapid host responses did not occur in non-Phi-treated inoculated seedlings. There was also a significant (P < 0AE001) decrease in lesion size in Phi-treated plants. These results indicate that Phi primes the plant for a rapid and intense response to infection involving heightened activation of a range of defence responses.

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Phosphite, an analog of phosphate is used to control oomycete diseases on a wide range of horticultural crops and in native ecosystems. In this study, we investigated morphological and transcriptional changes induced in Phytophthora cinnamomi by phosphite. Cytological observations revealed that phosphite caused hyphal distortions and lysis of cell walls and had an adverse effect on hyphal growth. At the molecular level, the expression levels of 43 transcripts were changed. Many of these encoded proteins involved in cell wall synthesis, or cytoskeleton functioning. The results of both the microscopic and molecular investigations are consistent with phosphite inhibiting the function of the cytoskeleton and cell wall synthesis.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT RESEARCH HIGHLIGHTS• P. cinnamomi survival propagules in annuals/herbaceous perennials in nature • Formation of stromata by Phytophthora cinnamomi, novel for the species • Dense oospore clusters of P. cinnamomi, forming viable colonies in new hosts • Thick walled chlamydospores inside naturally infected roots • Presence of haustoria suggest a biotrophic mode in asymptomatic host species M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT ABSTRACTStudies were conducted to determine how Phytophthora cinnamomi survives during hot and dry Mediterranean summers in areas with limited surviving susceptible hosts.Two Western Australian herbaceous perennials Chamaescilla corymbosa and Stylidium diuroides and one Western Australian annual Trachymene pilosa were collected weekly from a naturally infested site from the Eucalyptus marginata (jarrah) forest from winter to spring and less frequently during summer 2011/12. Selfed oospores, thick walled chlamydospores and stromata of P. cinnamomi were observed in each species. Oospores and thick-walled chlamydospores germinated in planta confirming their viability. This is the first report of autogamy by P. cinnamomi in naturally infected plants. Stromata, reported for the first time for P. cinnamomi, were densely aggregated inside host cells, and germinated in planta with multiple germ tubes with hyphae capable of producing oospores and chlamydospores.Trachymene pilosa was completely asymptomatic, S. diuroides did not develop root lesions but some plants wilted, whilst C. corymbosa remained asymptomatic above ground but lesions developed on some tubers. The presence of haustoria suggests that P. cinnamomi grows biotrophically in some hosts. Asymptomatic, biotrophic growth of P. cinnamomi in some annual and herbaceous perennials and the production of a range of survival structures have implications for pathogen persistence over summer and its management. KEYWORDSPhytophthora cinnamomi, survival structures, life cycle, facultative homothallic, biotrophic growth, endophyte, haustoria M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 2 INTRODUCTIONPhytophthora cinnamomi is a soil-borne root pathogen with a broad host range and necrotrophic mode of infection (Cahill et al. 2008; Zentmyer 1980) and results in the death of many susceptible plant species and the degradation of ecosystems worldwide including 15 global biodiversity hotspots (Dunstan et al. 2010). Phylogenetically and taxonomically, this pathogen belongs to the class Oomycetes in which swimming zoos...

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