Skip to main content
Premium Trial:

Request an Annual Quote

UC Riverside Team Reports Details of Small RNA Suppression in Plants by Key Pathogens

NEW YORK (GenomeWeb) – While the suppression of a plant's RNA silencing mechanisms is a well-known strategy for the highly destructive and widespread Phytophthora pathogens, the molecular interactions between these pathogens and their hosts is not fully understood.

But new research published this week by a team from the University of California, Riverside revealed that Phytophthora pathogens have evolved effectors capable of binding to an evolutionarily conserved plant protein that regulates the biogenesis and processing of both microRNAs and siRNAs, resulting in hypersusceptibility to infection.

Many Phytophthora pathogens are responsible some of the most economically important diseases in agriculture, affecting trees, ornamental plants, beans, and more. They are known to associate with host plants through infection structures called haustoria, through which cytoplasmic effectors are secreted and taken up by plant cells through a host-targeting motif.

Each Phytophthora species is believed to encode more than 1,000 of these cytoplasmic effectors, the majority of which contain the consensus RxLR motif, the UC Riverside team wrote in a paper appearing in the Proceedings of the National Academy of Sciences.

Much research has been conducted on identifying the virulence targets of Phytophthora effectors and it is known that a variety of plant processes are disrupted during Phytophthora infection.

In a previous study, for example, the UC Riverside investigators demonstrated that two P. sojae RxLR effectors, dubbed Phytophthora suppressors of RNA silencing 1 and 2 (PSR1 and PSR2, respectively), can suppress RNA silencing — a key viral defense system — in plants. The scientists also showed that transgenic plants expressing either PSR1 exhibited decreased abundances of miRNAs and siRNAs, leading to serious developmental defects.

Still, the host targets of PSR1 and the mechanisms by which it suppresses small RNA accumulation remained unclear. In a series of experiments in Arabidopsis detailed in PNAS, however, the investigators found that the effector directly interacts with a nuclear protein containing the aspartate-glutamate-alanine-histidine-box RNA helicase domain in the plant.

This protein, called PSR1-interacting protein 1 (PINP1), was further shown to be required for the accumulation of small RNAs and to be important to miRNA and siRNA biogenesis and processing in the plant, at least in part by influencing the assembly of dicing complexes.

Silencing of PINP1 resulted in developmental and immunity defects in Arabidopsis, with similar effects observed in Nicotiana benthamiana.

Taken together, the study results reveal PINP1 as a previously unidentified component of RNA silencing that can regulate different classes of small RNAs in plants, the researchers wrote in their paper. They also provide new insights into the pathogenic mechanisms of Phytophthora diseases.