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Nucleotide-binding domain and leucine-rich repeat (NLR) proteins make up the largest immune receptor family in plants. Although many studies have put effort into revealing the working mechanism of NLRs, the activation details of plant NLRs still remain obscure. Recently, two remarkable works resolved the structures of a plant NLR protein, the Arabidopsis thalianaHOPZ-ACTIVATED RESISTANCE1 (ZAR1), both in resting and activation states. The activated ZAR1 with its partner proteins form a wheel-like pentamer called resistosome that is thought to be able to trigger cell death by perturbing plasma membrane integrity. These findings greatly further our understanding of plant immune system.

The stepwise activation and proposed working model of ZAR1.

Plant diseases cause dramatic economic loss, posing a major challenge to modern agriculture. Plant pathogenic organisms secret effectors that utilize fascinating and intricate stratagems to facilitate infection. The consequences of plant-pathogen interactions are largely determined by effectors. The effector research has made great strides since its inception in the 1990s and the importance of effectors is increasingly noticed. Molecular investigation of effectors has provided critical insights into how plant pathogens manipulate their hosts to cause diseases. Thus far, numerous excellent reviews concerning effectors have focused on their targeting host pathways, recognition by host receptors, and evasion mechanisms, but few have ever summarized all known effector action modes. Here, we distinguish ten different stratagems of effector function from all types of pathogens, including damage, inhibition, hijacking, promotion, subversion, mimicry, reprogramming, evasion, decoying, and adaption. Furthermore, we discuss examples of these ten stratagems, refine the effector definition, and propose future directions of phytopathogenic effector research.

Potato late blight caused by Phytophthora infestansis one of the most destructive plant diseases that threaten global food security. Early and effective diagnosis of P. infestansis required before disease management decisions are made. Here, we developed a quick protocol to detect P. infestansbased on a loop-mediated isothermal amplification (LAMP) assay. The P. infestansspecific multiple copy DNA sequences (PiSMC), a transposon-like element, provides an ideal target for molecular detection of this pathogen. We designed highly specific and sensitive primers allowing effective LAMP detection of the pathogen at 64°C in 70 min. In the validation assay, all 15 P. infestansisolates collected from China, Europe and South America could be positively detected, but results of the other 9 Phytophthoraspecies infecting different plants, fungal and bacterial plant pathogens tested were negative. The detection limit of this assay is 1 pg P. infestansDNA. Moreover, the LAMP-PiSMCassay is able to detect P. infestansfrom infected leaves, tubers and soil. Taken together, this study reports the development of a specific and sensitive LAMP-PiSMCassay for early diagnosis of potato late blight.

Filamentous plant pathogen genomes often display a bipartite architecture with gene-sparse, repeat-rich compartments serving as a cradle for adaptive evolution. The extent to which this two-speed genome architecture is associated with genome-wide DNA modifications is unknown. We show that the oomycetes Phytophthora infestansand Phytophthora sojaepossess functional adenine N6-methylation (6mA) methyltransferases that modulate patterns of 6mA marks across the genome. In contrast, 5-methylcytosine could not be detected in these species. Methylated DNA IP sequencing (MeDIP-seq) of each species reveals 6mA is depleted around the transcription start sites (TSSs) and is associated with lowly expressed genes, particularly transposable elements. Genes occupying the gene-sparse regions have higher levels of 6mA in both genomes, possibly implicating the methylome in adaptive evolution. All six putative adenine methyltransferases from P. infestansand P. sojae, except PsDAMT2, display robust enzymatic activities. Surprisingly, single knockouts in P. sojaesignificantly reduce in vivo 6mA levels, indicating that the three enzymes are not fully redundant. MeDIP-seq of the psdamt3mutant reveals uneven 6mA methylation reduction across genes, suggesting that PsDAMT3 may have a preference for gene body methylation after the TSS. Furthermore, transposable elements such as DNA elements are more active in the psdamt3mutant. A large number of genes, particularly those from the adaptive genomic compartment, are differentially expressed. Our findings provide evidence that 6mA modification is potentially an epigenetic mark in Phytophthoragenomes, and complex patterns of 6mA methylation may be associated with adaptive evolution in these important plant pathogens.

In many eukaryotic organisms, Cdc14 phosphatase regulates multiple biological events during anaphase and is essential for mitosis. It has been shown that Cdc14 is required for sporulation in the potato blight pathogen Phytophthora infestans; however, the role that the Cdc14 homolog (PsCdc14) plays in the soil-borne soybean root rot pathogen P. sojaeremains ambiguous. PsCdc14is highly expressed in sporulation, zoospore, and cyst life stages, but not in vegetative mycelia and infection stages, suggesting that it contributes to asexual reproduction and thus the spread of the disease. Double-stranded RNA (dsRNA) mediates gene silencing, a post-transcriptional and highly conserved process in eukaryotes, involving specific gene silencing through degradation of target mRNA. We combined in vitrodsRNA synthesis and a polyethylene glycol-mediated transformation system to construct a dsRNA-mediated transient gene silencing system; and then performed a functional analysis of PsCdc14 in P. sojae. PsCdc14mRNA was dramatically reduced in transformants after protoplasts were exposed in in vitrosynthesized PsCdc14dsRNA, resulting in low sporangial production and abnormal development in P. sojaesilencing lines. Furthermore, dsRNA-mediated transient gene silencing could enable elucidation of P. sojaerapid gene function, facilitating our understanding of the development and pathogenicity mechanisms of this oomycete fungus.

Immune receptors at the plant cell surface can recognize invading microbes. The perceived microbial molecules are typically widely conserved and therefore the matching surface receptors can detect a broad spectrum of pathogens. Here we describe a family of Phytophthorasmall extracellular proteins that consists of conserved subfamilies that are widely recognized by solanaceous plants. Remarkably, one subclass of SCR74 proteins is highly diverse, restricted to the late blight pathogen Phytophthora infestansand is specifically detected in wild potato plants. The diversification of this subfamily exhibits signatures of a coevolutionary arms race with surface receptors in potato. Insights into the molecular interaction between these potato-specific receptors and the recognized Phytophthoraproteins are expected to contribute to disease resistance breeding in potato.