Review for secondary proposal, titled “Phytophthora infestans effector AVR1 targets host proteins and manipulates plant immunity”
Michelle Guo
Summary:
The oomycete, phytophthora infestans , is the causal pathogen for the late blight of potato, the cause of the notorious Irish Potato famine from 1845-1861. Eleven R genes identified from
Solanum demissum (wild potato), indicating 11 Avr genes exist in phytophthora infestans . Avr3a can be recognized by R protein R3a, leading to ETI; it can also target and stabilize CMPG1, an
E3 uniqutin ligase, to block cell death. Avr2 can be recognized by R2 and also interact with
BSL1, indication of an indirect recognition by R2. Avrblb1 directly interacts with Rpi-blb1 to trigger HR. Avrblb2 activates Rpi-blb2, leading to host defense, and it also targets PLCP
(papain-like cysteine protease), prevents it from secreting to the apoplast, leading to virulence.
Avr1 and R1 are under studied. The goal of the proposal is to better understand Avr1 and R1, and to develop better strategies to fight p. infestans in potato.
Hypothesis : In addition to triggering plant defense upon recognition by R1 protein, the effector
Avr1 also interacts with host proteins to suppress plant immunity.
The goal is to identify Avr1-interacting proteins involved in immune suppression in the host.
Approaches:
1. The PI proposed to identify Avr1-interacting proteins by Y2H-screen (study 1), to confirm the interactions through GST pulldown and BiFC (studies 2 and 3), to carry out structural and functional predictions (study 4), to map interaction domains by deletion and Y2H (study 5).
2. The PI proposed to examine Avr1 suppression of HR induced by 35 S-PtoY20 7D,
35S-INF1, 35S-CRN2 and 35S-AvrBs3 in N. benthamiana (study 1), to map interaction amino acids in Avr1 and Avr1-IP by mutagenesis of candidates residues followed by Y2H and transient expression (study 2), to examine if Avr1-induced HR suppression is affected by silencing Avr1-
IP (study 3), to determine if Avr1 recognition by R1 requires Avr1-IP through Y2H and N. benthamiana transient system (study 4).
3. The PI proposed to test Avr1 translocation by mutagenesis in RxLR motif and then fusion with GusA (study 1), and to examine Avr1 dimerization by Y2H (study 2).
4. The PI proposed to study the mode of action of Avr1 by mutagenesis (study 1), and to examine the influence of mutations on virulence by Avr1-IP knockdown (study 2) and overexpression (study 3).
Strength:
1. Potato is an important crop and proposed work could potentially contribute to the disease control;
2. The work plan is reasonable although objective 1 and 2 are a bit too ambitious;
3. The proposal is well presented regarding to personnel involved and delegation of the workload.
Weakness :
1. The title is too general, should be more specific to reflect the proposal;
2. From objectives 1, many candidate Avr1-interacting proteins could be identified, more analysis needs to be focused on prioritizing the candidates to be studied;
3. Study 3 from objective 2 is confusing (The effect of gene silence induced by
TRV/AVR1-IP is assayed through monitoring the decrease of AVR1-IP transcripts but not of its orthologs AVR2, AVR3a, AVR3b, AVR4
4. Most of the proposed scenarios are referred to Avr3a and the PI proposed a rather generic and open-ended approach for the study.
There is a good potential for the proposed study to be productive, by balancing out the four objectives and prioritizing the Avr1-interacting proteins, and employing more innovative approaches. I give it a rating of “very good”.