Exploring knowledge of gene function to combat pod shatter in oilseed rape

Successful domestication of seed crops depends on the plant's ability to hold on to its progeny until harvest. The problem of seed dispersal control in cereals was solved thousands of years ago through simple selective breeding, but remains a serious issue for oilseed rape. The average annual loss experienced by farmers due to premature fruit opening, known as pod shatter is >10%. This loss can exceed >70% under particularly windy conditions, when wet weather delays harvest or if a hailstorm hits the field when the crop is ripe. With an expanding human population and dramatic changes in climate patterns, the challenge to global food production has never been bigger, and to meet the demands it is essential that performance of our major crops be improved. However, the potential yield gain from such efforts cannot be fully realised if the farmer looses a significant part of his crop even before going out to harvest. Fruits from oilseed rape dry out at maturity and open to allow their seeds to be dispersed in a process known as pod shatter. Unfortunately, all the fruits in the field do not dry out at the same time making it difficult for oilseed rape farmers to time their harvest and obtain all the seeds. In addition to a significant yield loss, the prematurely released seeds fall to the ground and germinate to become weeds (volunteers) and contaminate the harvest of the following year. This severely inhibits the crop rotation practice used by many farmers and is therefore also damaging to the environment. Arabidopsis is a small, weedy plant that has been used as a laboratory model system to elucidate a wide range of aspects related to plant growth and development. Despite a dramatic size difference, fruits from Arabidopsis are remarkably similar to fruits from oilseed rape. In the past decade some of the key genetic regulators of fruit opening in Arabidopsis have been identified, and we have shown that these factors also function in species that are closely related to oilseed rape. In the proposed research project, we will exploit our knowledge to control pod shatter directly in high-yielding UK-elite oilseed rape varieties. Specifically we will manipulate and adjust the activity of a particular gene by the isolation of mutant plants and assessment of their performance in pod shatter-resistance tests. We will furthermore use mutated lines to expand our knowledge about the mechanism of fruit opening to enable us to fine-tune the pod shatter trait in future varieties. Particular strengths of this project are our genetic resources and our expertise in all the required technologies to successfully fulfill our objectives. In conclusion, we believe that the presented project will provide substantial benefits for both farmers and consumers, as well as for the environment.

The aim of this project is to introduce pod shatter resistance into modern oilseed rape varieties by modification of two paralogous genes. We have previously described how the INDEHISCENT (IND) gene regulates shattering in the model plant Arabidopsis and how this knowledge can be transferred to Brassica species such as B. rapa and B. oleracea. Here, resistant lines will be identified via TILLING (Targeting Induced Local Lesions IN Genomes) for mutations in the two B. napus IND genes. Single and double mutants will be characterised for their ability to fine-tune the shattering process and will be backcrossed to elite varieties for immediate use in breeding programmes. In addition to the significant commercial and environmental value of such lines, the experiments that we have planned will expand our knowledge on the molecular mechanism by which IND mediates its function. To this end, we will take advantage of a large allelic series of point mutations in the IND gene in B. rapa (BraA.IND). IND regulates hormone balance at the valve margin, and the mutant lines will be tested for their ability to create an auxin minimum and direct expression of the GA biosynthesis gene GA4. We have previously shown that IND can form homodimers in yeast and heterodimers with a related transcription factor, SPATULA. We will create site-directed mutants in the BraA.IND gene corresponding to those identified in the allelic series to map the domains required for these protein-protein interactions. In this way, the proposed project will drastically reduce and possibly eliminate pod shatter in oilseed rape and will advance our knowledge on fruit tissue-specification while developing tools for further fine-tuning of pod shatter resistance in future varieties.

Who will benefit from this research and how? Oilseed rape makes a considerable contribution to UK agriculture; currently ~20% to the total crop output per year is devoted to its production (information from The International Agri-Technology Centre). Production is increasing each year with an area of 581,000 ha of oilseed rape sown in 2009 producing 2.0 million tones (compared to 1.5 million tones in 2002). Still the UK imports more than 150,000 tonnes oilseed per year. The yield could be significantly improved by inhibiting premature pod shatter, which leads to annual losses of 15-20% on average but can exceed 70% under adverse weather conditions (see supporting letter from organic farmer, Philip Taylor). Besides resulting in an estimated loss of ~£60 million in the UK per year, the prematurely released seeds fall to the ground and germinate to become weeds (volunteers) and contaminate the harvest of the following year. This severely inhibits the crop rotation practice used by many farmers and is therefore also damaging to the environment. The output of this research will therefore be of value to all industries with interest in crop improvement. The agricultural industry/agronomists: The industry will benefit from the development of technologies to minimise seed loss due to unsynchronised seed dispersal. IP-free pre-breeding material will be made available for the industry with first-hand access to industrial members of CIRC. Farmers: Reduction in seed loss will increase the farmer's yield. The ~10% losses is an estimated average that hides the occasional disasters when strong winds or a hailstorm can cause >70% loss of yield. Importantly, the research proposed here will not only lead to increased yields, but the protection against the effect of adverse weather conditions will also make the yield more predictable. Public: The public would benefit from greater predictability of yields, through greater stability in production costs, which would impact on prices in the shops. There are also obvious environmental benefits using the technology described here. Oilseed rape has emerged as the second largest oilseed crop with an annual worldwide production of 38 million tons of oil and demand is increasing. For this to be sustainable, seed yield needs to be dramatically increased through more efficient breeding programmes while at the same time minimising the amount of fertiliser input in order to protect the environment. I believe the strategy adopted here will contribute significantly towards such a goal. What will be done to ensure that they have the opportunity to benefit from this research? Publications: Results will be published in high-impact scientific journals and the breeding/farming press in a timely fashion. It will also be presented at national and international conferences and trade shows. Collaborations: The PI has strong connections to the breeding industry and Brassica crop improvement programmes. The data and pre-breeding material that we obtain will be of immediate use to these interest groups for example via CIRC dissemination meetings and the Defra-funded Oilseed Rape Genetic Improvement Network (OREGIN) which brings together academic researchers and breeding companies to generate pre-breeding material. Commercialisation: Contacts with industrialists, biotechnologists and related umbrella organisations will be made through CIRC and OREGIN as soon as any exploitable results/materials are generated. The strategy we adopt will allow the IP-free pre-breeding material to be tested both at JIC and by our industry contacts at their sites. We will enquire with the breeding companies about suitable elite lines for backcrossing to facilitate the route to exploitation.