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Role of Auxin in Phytophthora Root Rot Disease Development in Soft Fruit


Project Description

Brief Introduction: Phytophthora species that infect soft fruit are currently poorly understood and understudied pathogens. They cause significant economic and environmental impact on soft fruit production in the UK. Phytophthora rubi in particular, is decimating soil based plantations and forcing farmers to adopt pot-based systems with almost annual replenishment of the plants. Plant based resistance is the only way forward but this requires knowledge of the effector arsenal by which this pathogen will be recognised by the plant. Raspberry cultivars with resistance to Raspberry Root Rot (PRR) disease have a stronger, more branched root system compared to susceptible cultivars. Auxin is a phytohormone which is known to control root elongation, lateral root formation and can indirectly modulate defences through crosstalk with plant defense pathways. Our research question is “What role might auxin play in plants challenged with Phytophthora and how can this knowledge be applied to combat Raspberry root rot disease”.

Preliminary results
There is significant expertise at the James Hutton Institute in the study of oomycete pathogens that infect crops and trees. The James Hutton Institute also has a strong history in soft fruit breeding and possess an historical collection of P. rubi and P. fragariae isolates and extensive expertise in the pathology of oomycetes. The mutual antagonism between growth and defense responses has been an area of study by EG for around 5 years. In particular, Turnbull et al., 2017 shows that another growth promoting pathway (controlled by the phytohormone Brassinosteroid) is antagonistic to early defense mechanisms in potato. In addition, an AHDB funded studenthip awarded to EG has already successfully developed a hydroponic system that allows raspberries to be grown easily, with easy access to the roots for clean and efficient infection assays. Furthermore, fluorescently labelled isolates of P. rubi have been generated, allowing infection steps to be easily traced in real-time thus enabling us to exploit the world-leading expertise at the James Hutton to monitor infection in planta in controlled environments.

Previous studies of raspberry cultivars Glen Moy (PRR susceptible) and Latham (PRR resistant) in the James Hutton Institute raspberry group found that root rot scores were negatively correlated with measures of root vigour. Strikingly, auxin responsive and root development genes are significantly induced during attempted PRR infection in PRR resistant Latham. Auxin is the dominant regulator of lateral root development in plants. Previous work at the James Hutton Institute by CS has shown that the Auxin responsive genes ABP19a and CTR1, map closely to the commercially important simple sequence repeat marker Rub118b 110 bp. This marker is highly correlated with PRR resistance and is the only marker linked to Latham PRR resistance that is unbroken.

ABP19 has been subject to further studies at the James Hutton Institute by EG through 2018 in resistance to P. infestans infection in the model plant N. benthamiana. Virus-induced gene silencing of NbABP19 resulted in phenotypes consistent with disrupted auxin physiology and, importantly, exhibited a negative impact on P. infestans leaf colonisation. Conversely, the exogenous application of auxin significantly increased the occurrence on P. infestans infection on leaves. Furthermore, we have preliminary evidence that the auxin transport inhibitor TIBA significantly perturbed P. infestans growth in vitro plate assays.

Funding Notes

The PhD position is a joint research project between the James Hutton Institute, and the University of Warwick where the student will be registered. The position is fully funded according to UKRI rates. Applicants should have a first-class honours degree in a relevant subject or a 2.1 honours degree plus Masters (or equivalent).

References

1. Graham J, Hackett CA, Smith K, Woodhead M, MacKenzie K, Tierney I, Cooke D, Bayer M, Jennings N. (2011) Towards an understanding of the nature of resistance to Phytophthora root rot in red raspberry. Theor Appl Genet. 123:585-601.
2. Ohmiya, A. 2002. Characterisation of ABP19/20, sequence homologues of germin-like protein in Prunus persica L. Plant Science, 163: 683-689
3. Turnbull D, Yang L, Naqvi S, Breen S, Welsh L, Stephens J, Morris J, Boevink PC, Hedley PE, Zhan J, Birch PRJ, Gilroy EM.
(2017) RXLR Effector AVR2 Up-Regulates a Brassinosteroid-Responsive bHLH Transcription Factor to Suppress Immunity. Plant Physiol. 174:356-369.
4. Yang L, McLellan H, Naqvi S, He Q, Boevink PC, Armstrong M, Giuliani LM, Zhang W, Tian Z, Zhan J, Gilroy EM, Birch PR (2016) Potato NPH3/RPT2-Like Protein StNRL1, Targeted by a Phytophthora infestans RXLR Effector, Is a Susceptibility Factor. Plant Physiol. 171:645-57.
5. Eshraghi L, Anderson JP, Aryamanesh N, McComb JA, Shearer B, Hardy GS (2014) Suppression of the auxin response pathway enhances susceptibility to Phytophthora cinnamomi while phosphite-mediated resistance stimulates the auxin signalling pathway. BMC Plant Biol. 20;14:68.
6. Robert-Seilaniantz A, Grant M, Jones JD (2011) Hormone crosstalk in plant disease and defense: more than just jasmonate-salicylate antagonism. Annu Rev Phytopathol. 49:317-43.


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