Abstract
Phytophthora spp. cause serious damage to plants by exploiting a large number of effector proteins and small RNAs (sRNAs). Several reports have described modulation of host RNA biogenesis and defence gene expression. Here, we analysed Phytophthora infestans Argonaute (Ago) 1 associated small RNAs during potato leaf infection. Small RNAs were co-immunoprecipitated, deep sequenced and analysed against the P. infestans and potato genomes, followed by transcript analyses and transgenic assays on a predicted target. Extensive targeting of potato and pathogen-derived sRNAs to a range of mRNAs was observed, including 638 sequences coding for resistance (R) proteins in the host genome. The single miRNA encoded by P. infestans (miR8788) was found to target a potato alpha/beta hydrolase-type encoding gene (StABH1), a protein localized to the plasma membrane. Analyses of stable transgenic potato lines harbouring overexpressed StABH1 or artificial miRNA gene constructs demonstrated the importance of StABH1 during infection by P. infestans. miR8788 knock-down strains showed reduced growth on potato, and elevated StABH1 expression levels were observed when plants were inoculated with the two knock-down strains compared to the wild-type strain 88069. The findings of our study suggest that sRNA encoded by P. infestans can affect potato mRNA, thereby expanding our knowledge of the multifaceted strategies this species uses to facilitate infection.
Highlights
Noncoding small RNAs are known to be important regulators of gene expression
We infected potato leaves with the P. infestans PiAgo1-green fluorescent protein (GFP) strain, and included as controls leaves infected with a strain containing pHAM34:GFP (Avrova et al, 2008) (Fig. S1) and mycelia from the two strains grown on plates
Computational processing (Fig. S2) resulted in six small RNAs (sRNAs) datasets comprising 26 123 643 sRNA reads from P. infestans and 3 090 568 potato sRNA reads
Summary
Noncoding small RNAs (sRNAs) are known to be important regulators of gene expression. They have been studied extensively in several eukaryotic model species, including Arabidopsis, because they are involved in numerous processes, such as development, maintenance of genome integrity, and stress responses (Axtell, 2013). 21–24 nucleotide (nt) sRNAs are processed from RNA polymerase II-transcribed primary RNAs (microRNAs or miRNAs) or generated from dsRNA. Among the latter group, secondary small interfering RNAs (siRNAs) such as phasiRNA and tasiRNAs can be formed. Additional proteins take part in transcriptional and post-transcriptional gene silencing events that
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