Yield improvement of oilseed rape through genetic manipulation of rhizosphere exudation

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Healthy roots pass large amounts of C into soil as rhizodeposits. The function of some rhizodeposit components is known, but that of others is unclear. Rhizodeposits massively stimulate microbial populations in the rhizosphere. The aim of this work is to identify genes controlling rhizodeposition in oilseed rape (OSR) and the effect of developmental stage on rhizodeposition. We will then investigate how genetic control of rhizodeposition could be used as a tool to engineer rhizosphere microbiology to promote functions beneficial to crops.

Genetic variability in rhizodeposition between OSR genotypes at different developmental stages will be determined using 14C pulse-labelling. The chemistry of the major rhizodeposit pool and soluble exudates, will be determined by measuring the secreted metabolome, including organic acid, carbohydrate and amino acid pools using a range of techniques, including the cutting edge technique FTICR-MS which provides ultra-high resolution and accuracy of complex organic mixtures. Exudate chemistry will be analysed in mapping lines with parents shown to have maximum differences in rhizodeposit chemistry, to identify QTL controlling exudate characteristics. High throughput sequencing will be used to investigate the root transcriptome and identify genes associated with rhizodeposition. Using contrasting lines in which genes controlling exudation have been identified, we use cutting edge metagenomic techniques to study the impact of rhizodeposit characteristics on microbial community functioning. We will also investigate how those genetic regions we identify which control rhizodeposition influence crop yield in the field.

The work will identify genes which could be used by OSR breeders to alter rhizodeposition to increase yield, by altering C partitioning within the plant, changing rhizodeposit content to enhance nutrient uptake, or engineering rhizosphere microbes to promote functions beneficial to the plant.

The scientific objectives of this project are given in the case for support; the project also has the following objectives aimed at transferring material and knowledge to industrial members of the CIRC:

Lines possessing beneficial alleles at QTL for rhizodeposition traits (quality and quantity) will be identified for use in OSR breeding and released to breeding companies for crossing with elite lines (WP1 and 2; month 24)

The genetic markers flanking the QTL will be identified and released to breeding companies for use in marker assisted selection in breeding for rhizodeposition traits (WP2; month 24)

Knowledge will be made available as to whether variation in rhizodeposition impacts on yield either directly or via manipulation of the soil microbiota and its ability to make P available to the plant at industry levels currently used by OSR growers (WP 4 and 5; month 36)

Knowledge of the role of genotype x environment on rhizodeposition will be communicated to breeders to allow them to judge the value of breeding for the trait (WP4; month 36)

These objectives will be met by the work under WP1,2,4, and 5 described in the case for support. In addition, if work in WP3 identifies genes which appear to be associated with variation in rhizodeposition gene specific markers can be developed for use in marker assisted selection.

The reporting structure of the CIRC will provide regular fora for exchange of information to club members. In addition we have regular contact with the breeding company members of the club through the project advisory committee, our collaborations in the Oilseed Rape Genetic Improvement Network (OREGIN) and prior to submission of the full proposal have consulted with representatives regarding the commercialisation of the research outputs taking their views into account in writing the full proposal.

The results of the research will be communicated through additional routes to increase its impact, including publications in leading peer-reviewed journals specializing in plant science and soil and / or environmental microbiology, presentations at key scientific conferences (14th International Rapeseed Congress in (Saskatoon, 2015), and either the 20th World Congress of Soil Science (South Korea, 2014), Rhizosphere IV (2014) or the International Symposium of Microbial Ecology (2014)). Further publicity of the project and scientific progress will be made through dedicated project Web pages of the project's ost institutions, the OREGIN and Brassica.info websites and other media as deemed appropriate. Prior to publication of results permission will be sought from the CIRC as specified in the special conditions for this BBSRC initiative.

Although the OSR breeding industry will be the primary route for delivery of the applied outcomes of this research, the impact of the findings will have a much wider scope. For instance, farmers will benefit with improved profitability due to increased yields and more effective use of fertilizer applications. The environment will benefit through less fertilizer being wasted by the crop and possibly less fertilizer being applied. Increasing yield per acre of farmland also contributes to feeding the increasing population without extensive land use change. One of the outcomes may be an improvement in P use efficiency which will have implications for extending the utility of the finite resource of economically extractable mineral P.