Recently, the mbio Journal of American Society of Microbiology (ASM) published the paper "divergent evolution of PCF / scr74 effectors in oomycetes is associated with distinct recognition patterns in solanaceous" published by Dr. vivianne g. A. a. vleeshowers, plant breeding group of Wageningen ur University in the Netherlands Plants, for the first time, reported that PCF / scr74 effectors in oomycetes could have both PAMP and effector characteristics.
nearly 15 years have passed since nature published the plant immune system in 2006 (Jones and Dangl, 2006).
in this classic review, the plant immune system is divided into membrane receptor-mediated PTI (PAMP triggered immunity) and intracellular NLR receptor mediated ETI (effector triggered immunity), respectively.
however, with more and more new discoveries in the past 15 years, this binary classification can not describe all the conditions of plant immune system perfectly. For example, some immune receptors on the membrane recognize PAMP which is not pathogen, It is an extracellular effector. We should call the immune response mediated by PTI or ETI? According to the systematic summary in the two subsequent reviews, PAMP and effector can not be divided into two parts in many cases. Therefore, it is difficult to describe the plant immune system perfectly only with PTI and ETI, and an invasion model (thomma et al., 2011; cook et al., 2015) is proposed.
Phytophthora belongs to oomycete, including many important plant pathogenic microorganisms. Among them, the most famous Phytophthora infestans triggered the great famine in Ireland in 1845, causing more than one million deaths.
it can cause late blight on Solanaceae plants such as potatoes and tomatoes, and is still a major plant disease in the world.
other Phytophthora cactorum can cause strawberry root rot.
these Phytophthora pathogens can secrete some extracellular effectors, many of which are small cysteine rich proteins (SCR). PCF is identified from P. cactorum and can trigger cell necrosis in strawberry leaves. It was once considered as a toxin (orsomando et al., 2003).
however, the expression of scr74 was up-regulated in the process of P. infestans infection, and the scr74 family was strongly positive selection (Liu et al., 2005). However, the function of PCF / SCR proteins is still unknown.
in this study, the authors first discovered all small cystene rich (SCR) proteins containing PCF motif through public databases and published oomycete genomes.
after clustering by split network method, we found that PCF protein is relatively conservative, and homologous protein can be found in many oomycetes, while scr74 only exists in P. informatics.
through further analysis, we cloned PCF genes from different P. cactorum races in America and Europe, and found that their sequences are highly conserved, while the orthologous genes of PCF gene in different oomycetes have a collinear pattern.
however, scr74 is completely different. This family only exists in P. informatics. The sequence is very variable and is subject to positive selection (Liu et al., 2005).
from this point of view.
PCF is in line with the characteristics of PAMPS, while scr74 is more like an effector.
after that, in order to understand the recognition of these extracellular effectors in plants, the authors selected 13 scr74 family proteins, PCF proteins, and some other SCR proteins, using effector omics A total of 245 Solanaceae materials were screened with high-throughput functional screening strategy, including 206 wild potato, 23 tomato, 7 eggplant, 10 pepper and 8 tobacco genotypes.
we found that PCF can trigger cell necrosis in many different species, including wild potato, tomato, eggplant, pepper and tobacco, as well as strawberry (orsomando et al., 2003).
however, the identification of scr74 was limited to wild potatoes.
many proteins of scr74 family differ only in a few amino acids, but their recognition patterns in wild potatoes are quite different.
from the perspective of recognition, PCF is more like PAMP and can be widely recognized in plants of different families, while scr74 is more like an effector. It is speculated that the receptor of scr74 evolves independently in the wild potato population, and scr74 and potential potato receptors are undergoing "military competition" coevolution.
in another report this year, we developed RLP / RLK enrichment sequencing, and used this method to fine localize scr74-b3b receptor to a g-lecrk site in Solanum microdontum subsp. Gigantophyllum (gig362-6) (Lin et al., 2020).
in this study, the author sequenced another haplotype in gig362-6, and found that the copy number of g-lecrk gene in different haplotypes of gig362-6 was different. The author also analyzed the same site in other Solanaceae genome, and found that the copy number of this site in wild potato was higher than that in other Solanaceae species, and the copy number of these g-lecrk genes was very different Big.
therefore, the authors speculate that these g-lecrk proteins are probably receptors of scr74 effectors, and they are undergoing coevolution.
next, the functional verification of these g-lecrk proteins needs to continue.
therefore, this study reported for the first time that PCF / scr74 effectors in this kind of oomycetes could have the characteristics of PAMP or effector simultaneously. The idea of high-throughput screening plant populations by effector omics also laid the foundation for large-scale cloning of immune receptors on plant membrane.
the study was carried out by Dr. vivianne g.a.a. vleeshowers of the plant breeding group of Wageningen ur University in the Netherlands, Sophien kamoun team of the Sainsbury laboratory, and Paul birch team of James Hutton Institute and Dundee.
the first author is Dr. Xiao Lin of Wageningen University in the Netherlands and is now a postdoctoral fellow of the Sainsbury laboratory in the UK.
the study was funded and supported by the program of studying abroad sponsored by the National Council for study abroad, NWO, the Netherlands. References: cook, D.E., mesarich, C.H. and thomma, b.p.h.j. (2015) understanding plant immunity as a surveillance system to detect invasion. Annu. Rev. Polyphathol., 53, 541-563.jones, j.d.g. and Dangl, J.L. (2006) the plant immune system, nature, 444, 323-329-329.lin, X., Armstrong, M., Baker, K., Wolters, D., Visser, r.r.r.r.r., R.L. (2006) 2006) the plant immune system, nature, 444, 323 – 329.lin, X., Armstrong, M., M., Baker, K., Wolters, D., D., Visser, r.r.r.r.r.r.r., r.r.r., R.R., r.g.f., Wolters, P.J., Hein, I. and Vleeshouwers, V.G.A.A. (2020) RLP/K enrichment sequencing; a novel method to identify receptor-like protein (RLP) and receptor-like kinase (RLK) genes. New Phytol.Liu , Z., Bos, J.I.B., Armstrong, M., et al. (2005) Patterns of diversifying selection in the phytotoxin-like scr74 gene family of Phytophthora infestans. Mol Biol Evol, 22, 659–672.Orsomando, G., Lorenzi, M., Ferrari, E., de Chiara, C., Spisni, A. and Ruggieri, S. CMLS, cell. Mol. life SCI., 60, 1470 – 1476. Thomma, b.p.h.j., n ü rnberger, T. and Joosten, m.h.a.j. (2011) of PAMPS and effectors: the red pti-eti dichotomy. The plant cell, 23, 4 – 15. Thesis papers, papers, 23, 4 – 15.Link: