Elucidating the role of ROS in mediating self-incompatibility induced PCD

Lead Research Organisation: University of Exeter
Department Name: Biosciences


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Technical Summary

(A) Live-cell imaging of Arabidopsis SI lines expressing genetically encoded markers, including roGFP-Orp1 H2O2 sensors, in combination with markers/probes for various cellular organelles, will establish the intracellular sources of SI-induced ROS.

We will use the cell permeable sulfenic acid probe BCN-E-BCN, which traps sulfenic acids and, through linkage with Alexafluor dyes, allows for the fluorescence detection of sulfenylation in situ, to track the subcellular location of protein oxidation in pollen during SI.

(B) We will conduct 14C-glucose labelling assays to determine the SI-ROS induced changes in glycolytic metabolism in pollen tubes.

Using fluorometric and luminescence-based assays, we will determine if the activity of GAPDH and enolase, both subject to oxPTMs, are affected by SI-induced ROS. We will measure glycolytic/TCA cycle intermediates using LC-MS and GC-MS.

We will measure SI-induced changes in pollen energy charge using an ATP luminescence assay with luciferin. In addition, we will use a FRET-based biosensor for ATP, ATeam1.03-nD/nA, to monitor dynamics of ATP production in Arabidopsis pollen tubes and determine how this changes after SI.

We will use pharmacological inhibitors for ATP synthase, hexokinase and GAPDH, in combination with caspase-activity assays, to establish a link between reduced energy metabolism and PCD.

PM H+-ATPase (AHA7/8) T-DNA mutants in the Arabidopsis SI background will be used to evaluate their functional involvement in SI-PCD. The ratiometric pH sensor (phGFP) will be used to investigate a mechanistic link with SI-induced acidification.

We will determine SI-induced changes in the localization of GAPC in Arabidopsis "SI" plants by expressing an FP version.

(C) A series of biochemical assays with recombinant Papaver actin and ABPs, both containing oxidation resistant substitutions, will determine if oxidative modifications affect actin assembly/disassembly, and interactions with ABPs in vitro.

Planned Impact

Economic & Social Impact: Longer term, knowledge about self-incompatibility (SI), including understanding of how SI induced ROS are mechanistically involved in SI-PCD, may provide solutions to currently expensive F1 breeding systems. F1 hybrids are generally better and more productive than their parents, offering significant benefits to growers in terms of yield improvement, agronomic performance and consistency of end-use quality. Not surprisingly, hybrid seed comprises ~40% of global seed sales (worth billions p.a.). In the UK, for example, sugar beet, forage maize and many vegetable crops are all grown from F1 hybrid seed. Hybrid varieties also account for an increasing share of the rapeseed and winter barley market, and new hybrid wheat varieties have recently been introduced. Currently plant breeders have to hand-emasculate flowers to produce F1 hybrids. This is time-consuming and expensive. The introduction of the Papaver SI system to crops provides a potential route to produce F1 hybrids more easily and more economically. If a crop expresses the SI-PCD system it does not need to be emasculated, as all crosses will result in hybrid seed. The successful transfer of the Papaver SI system to Arabidopsis raises the possibility that a similar functional transfer is possible to other dicot crops, or even to the more distantly related grasses. This would mark a highly significant biotechnological break-through that could lead to a change in public-good and commercial breeding practises around the world. The ability to more effectively capture hybrid vigour in food crops would have profound food-security implications.
Another area through which knowledge about SI-PCD can potentially contribute to Economic and Social Impact is the development of new herbicides. Efficient herbicide systems for weed control are essential to safeguard crop yield. However, wWeeds are increasingly resistant to currently used herbicides. PCD constitutes a source of unexplored molecular targets for new herbicidal modes of action. Such new targets would avoid the use of toxic chemicals, benefiting the farmers, the agro-chemical industry, the environment and the wider public.
Fulfilling BBSRC strategic aims: This proposal sits firmly within the "Understanding the rules of life - promoting creative, curiosity-driven frontier bioscience to address fundamental questions in biology" remit of BBSRC described in the Forward Look for UK Bioscience document. While the science we propose is fundamental, there are potential applications for SI in the future (see above). Use of SI could impact on the BBSRC research priorities of "Sustainably enhancing agricultural production" and "Agriculture and food security". Providing enough food for the world is a major challenge. More economic ways to make F1 hybrid crops with better yields could provide an important contribution. Likewise, increasing our knowledge of PCD in plants can lead to the development of an innovative weed resistance management strategy. In addition, elements of the proposed research associate with "Systems approaches to the biosciences" and "Technology development for the biosciences". The proposal benefits from an "International partnership" with Shanjin Huang, Tsinghua University , Beijing, China.

The proposed research also aligns with the three themes highlighted in BBSRC's forward look for the UK bioscience: "Advancing the frontiers of bioscience discovery", "Tackling strategic challenges" (in particular "Bioscience for sustainable agriculture and food"), and "Building strong foundations".

The proposed collaborative project is novel, cutting edge, internationally competitive science and builds on well-established, high impact research, which underpins possible solutions to food security. Importantly, funding of this project is essential for the continuation of this high impact, and mostly BBSRC funded, research on plant cell signalling and PCD for the future.


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Description We have found new rapid responses in the self incompatibility response that prevents pollen germinating on its "own" stigma. We have used a genetically encoded hydrogen peroxide probe (roGFP-Orp1) directed to specific parts of the pollen tube cell to show rapid increases in hydrogen peroxide in mitochondria and plastids as well as cytoplasm. This is associated with a rapid decrease in respiration rate and activity of a respiratory enzyme (glyceraldehyde 3-phosphate dehydrogenase). These responses eventually result in programmed cell death of pollen tubes on the wrong stigma and thereby prevent self-fertilization.
Exploitation Route Understanding self incompatibility has potential for plant breeding
Sectors Agriculture, Food and Drink