Enhancing Internal Phosphorus Use Efficiency in Crops

1. Enhancing internal phosphorus use efficiency in crops: concepts and approaches Terry Rose, Southern Cross Plant Science/Southern Cross GeoScience

2. Internal phosphorus use efficiency • Three main ways we examine it: • Molecular and physiological responses from P starved model plants (e.g. arabidopsis) • Investigate mechanisms in highly P-efficient non-crop species • Investigate and attempt to exploit genetic variation within a crop species

3. Definitions of Internal Phosphorus Use Efficiency • Grain yield per unit of P in above-ground tissue (g mg-1) - yield formation may be independent of P use - selects against genotypes with low grain yield potential • Biomass yield per unit of P in above-ground tissue (g mg-1) - inverse of tissue P concentration • Critical shoot P concentration for 90% maximum yield (mg g-1) - expensive when screening large numbers • Shoot biomass/shoot P concentration (g2 mg-1) www.scu.edu.au/scps/

4. Problem caused by differential P uptake 29 rice genotypes grown in low P soil for 50 d with four replicates www.scu.edu.au/scps/

5. Can screening at equal P uptake help? www.scu.edu.au/scps/

6. Screening large numbers in hydroponics GWAS study needed +P controls for two reasons: • Can remove any genotypes that grew poorly in +P from any analyses – poor growth at low-P not related to low P but other artefacts • Can map GWAS peaks under +P conditions to find loci related to ‘general vigour’ and not specifically related to P www.scu.edu.au/scps/

7. Genome-wide association study (GWAS) for PUE Main QTL on chromosomes 1 (indica) and 11 (aus) www.scu.edu.au/scps/

8. Does internal PUE ranking change with shoot P content? There is no presumption that high internal PUE lines will grow well in the field because they may lack P uptake genes: The aim is to find loci/gene(s) that can be ‘pyramided’ into elite lines in local breeding programs. www.scu.edu.au/scps/

9. What are the consequences of higher internal PUE ? These authors apply ‘The law of conservation of matter’ to nutrient use efficiency. www.scu.edu.au/scps/

10. What are the consequences of higher internal PUE ? Source: Rose et al. 2013 Frontiers in Plant Science www.scu.edu.au/scps/

11. What are the consequences of higher internal PUE ? • Obtained same biomass as the wild-type plants with a quarter of the P content in shoots, while seed yield was not reduced. • No seed P concentrations shown www.scu.edu.au/scps/

12. What are the consequences of lower seed P concentrations? • Grain quality – milling traits in rice, dough quality in wheat? • Human health 1. P deficiency in humans? Unlikely. 2. phytate - Some reports suggest it may have anti-cancer properties, recent review by Kumar et al. (2010) suggests that there is limited evidence for this - Strong evidence for its role in binding micronutrients, so reduction in phytate may be beneficial 3. phospholipids - play a role in grain quality and human health, but may be quite stable (Tong et al. 2014) www.scu.edu.au/scps/

13. What are the consequences of lower seed P concentrations? • Seedling germination and vigour Two lines of enquiry have led to the conclusion that reducing seed P is detrimental to seed germination and vigour. • Studies with low phytic acid (lpa) mutants - Low-phytic-acid mutants often have impaired germination and vigour BUT this is because whole genes are often knocked out - The only LPA mutant used in breeding programs (Barley lpa1-1; Bregitzer et al. 2007 Crop Science) has no impact on seedling vigour BUT this mutant has a 10-14% reduction in seed total P due to mutation of a putative sulfate transporter. www.scu.edu.au/scps/

14. Seed germination and seedling vigour 2. Studies with low-P seed from P-starved plants • Half a dozen studies with cereal crops where low-P seed have shown reduced germination and seedling vigour compared to high-P seed • These studies do NOT make fair comparisons because the low-P seed came from P-stressed parent plants • Most studies were not conducted with agricultural soils with a history of P fertilisation, so soils were typically highly P-deficient. www.scu.edu.au/scps/

15. Seed germination and seedling vigour 2. Studies with low-P seed from P-starved plants • Seeds from P-starved plants performed poorly in P-deficient soil but no yield difference in agricultural soil supplied with P fertiliser • Subsequent studies with seed lower in P from environmental effects found no difference in seedling vigour between high- and low-P seed on any soil • Further studies have been conducted and will be the focus of the presentation by Elke Vandamme www.scu.edu.au/scps/

16. High P input farming systems • If seedling vigour can be maintained with lower seed P, then perhaps we could breed for lower seed P concentrations regardless of internal PUE at the vegetative stage. Go for high P uptake and low translocation to grains. • May be a useful trait in high-input farming systems where the removal of P in grains is significant and drives the need for continual P fertiliser input World phosphate deposits: FAO data Australian deposits are < 1 % of world P resources. Over 70 % of resources are held by China and Morocco. www.scu.edu.au/scps/

17. High P input farming systems www.scu.edu.au/scps/

18. High P input farming systems www.scu.edu.au/scps/

19. High P input farming systems www.scu.edu.au/scps/

20. High P input farming systems www.scu.edu.au/scps/

21. High P input farming systems • In an average season in Australia, approximately 60, 000 tonnes of P (the equivalent of over half a million tonnes of super phosphate) is removed off-farm in wheat grain at harvest assuming grain contains 3 mg P/g. • Most is exported overseas while some is consumed domestically and contributes to high-P landfill and the pollution of water bodies in Australia. • A reduction in grain P concentrations to 2 mg P/g would save about $100 million being removed off farm each year at $5 per kg P. www.scu.edu.au/scps/

22. Current research project: • Global Rice Science Partnership (SCU, JIRCAS, IRRI, AfricaRice) project aims to reduce rice grain P by minimum 20% • Approaches for breeding crops with low grain phosphorus • Two approaches investigated in the project: • Exploiting genotypic variation • Molecular approach • Mutant approach – not investigated but may be an option later www.scu.edu.au/scps/

23. GRiSP project: Exploiting genotypic variation Multi-location trials with 20+ rice genotypes over a number of years to look at G x E interactions for grain P concentration 1. Need to identify a genetic component that is independent of grain yield (yield-dilution effect) 2. Need to make sure low grain P isn’t associated with low plant P uptake! Elke Vandamme will be presenting data on this www.scu.edu.au/scps/

24. GRiSP project: Molecular approach Identify P transporter(s) and use RNAi silencing to reduce gene expression in specific tissue at a specific time Understand regulatory pathway of genes involved in grain P loading and find targets for genetic manipulation www.scu.edu.au/scps/

25. Summary • We have investigated internal PUE at the vegetative stage using a method which screens at equal P uptake and have mapped loci for high internal PUE • The consequences of high internal PUE will likely be a reduction in grain P concentration • Reducing grain P concentration may be a good option by itself, particularly in high-input systems • Further work is needed to ensure lower grain P concentration does not adversely affect grain quality or seedling vigour www.scu.edu.au/scps/

26. Acknowledgements • Southern Cross University • Cecile Julia • Kwanho Jeong • Alicia Hidden • Rachel Wood • Japan International Research Centre for Agricultural Science • Matthias Wissuwa • Asako Mori • Juan Pariasca-Tanaka • Katsuhiko Kondo • Africa Rice • Elke Vandamme • Kazuki Saito • IRRI • Tobias Kretschmar • Funding Agencies • Global Rice Science Partnership • Japan Society for the Promotion of Science www.scu.edu.au/scps/