Pathogen Virulence Proteins Suppress Plant Immunity

VBI Professor Brett Tyler and members of his research group, along with researchers from Virginia Tech's Department of Plant Pathology, Physiology and Weed Science, Nanjing Agricultural University in China, and Wageningen University in The Netherlands, examined the function of the virulence (or effector) protein Avr1b in P. sojae and discovered that Avr1b is capable of suppressing an important process in plant immunity called programmed cell death.

Programmed cell death is an in-built suicide mechanism that kills infected plant tissue and fills it with toxins so the pathogen can no longer feed on it. The work appears in the advance online edition of The Plant Cell. ⁽¹⁾

P. sojae is an oomycete plant pathogen that causes severe damage to soybean crops, resulting in $1-2 million in annual losses for commercial farmers in the United States and much more worldwide. By changing key amino acid residues in the effector protein, the researchers were able to attribute the cause of the suppression of programmed cell death to the presence of two conserved sequences (dubbed W and Y motifs) at one particular end of the protein, the C-terminus. These amino acid sequences are also present in many other members of a huge virulence gene superfamily that Tyler's group found recently in oomycete pathogens. ⁽²⁾

According to VBI Professor Brett Tyler, "Our results suggest that, like many human viruses such as HIV, oomycete plant pathogens disable the immune systems of their victims as part of their infection strategy."

(1) Daolong D, Kale SD, Wang X, Chen Y, Wang Q, Wang X, Jiang RHY, Arredondo FD, Anderson RG, Thakur PB, McDowell JM, Wang Y, Tyler BM (2008) Conserved C-terminal motifs required for avirulence and suppression of cell death by Phytophthora sojae effector Avr1b. The Plant Cell Published on April 4, 2008; 10.1105/tpc.107.057067.

(2) Jiang R, Tripathy S, Govers F, Tyler BM (2008) RXLR effector reservoir in two Phytophthora species is dominated by a single rapidly evolving superfamily with more than 700 members. Proc. Natl Acad. Sci. USA 105(12): 4874-4879.

The research was supported by funding from the National Research Initiative of the United States Department of Agriculture's Cooperative State Research, Education and Extension Service, the National Science Foundation, the Government of China, and the Netherlands Genomics Initiative.