PtRTP1, an Effector of Puccinia triticina, Contributes to Virulence in Wheat

Effector proteins are key virulence factors of obligate parasitic fungi during infection. Wheat leaf rust by Puccinia triticina is a widespread destructive disease drastically limiting wheat production, while the biological role of its effector is still elusive. PtRTP1 is a homolog of Uf-RTP1p, one of the earliest effector proteins verified to localize at the host-pathogen interface. Clarifying PtRTP1 function helps uncover rust pathogenic mechanisms; hence, we cloned PtRTP1 from P. triticina. The gene has a 1453 bp DNA sequence and a 777 bp CDS, encoding a protein with a 23 aa signal peptide, nine cysteines and two N-glycosylation sites. PtRTP1 was differentially expressed during infection, peaking at 24 hpi. Its expression pattern was consistent across races, with higher levels in the highly virulent strain THTT. Analysis of the nucleotide-sequence polymorphism of PtRTP1 from nine physiological races of P. triticina revealed two polymorphic sites. Heterologous expression assays demonstrated that the PtRTP1 protein could suppress BAX-induced programmed cell death and functioned in the nucleus. Host-induced gene silencing revealed that silencing PtRTP1 weakened fungal pathogenicity, reducing pustules and infection areas in wheat lines TcLr15 and TcLr36. This indicates secreted PtRTP1 acts as a virulence factor.