Improving radiation use efficiency in tropical rice

Transcription

1 Improving radiation use efficiency in tropical rice Erik Murchie Agricultural & Environmental Sciences

2 This talk 1. Radiation use efficiency (RUE) in tropical rice 2. Photosynthesis and RUE in the field. 3. Improvement of RUE: ways forward Transcriptomics of light-responses Transgenic rice Mutant screening

3 Rice farming is the single largest use of land for food 90 % of this is in Asia Only 6 7 % of all rice is exported from country of origin Rice forms around 60 % of daily calories for half the world s population It is the single largest source of food, employment and income for the world s poor IRRI estimate % increase in grain yields ha -1 in next 30 years. Large part of this must come from irrigated rice in Asia, if water supplies are maintained. Genome sequenced. Rice Almanac (2002): IRRI, CIAT, FAO

4 Stagnation of rice yield potential in the tropics Year World rice Asian irrigated rice production production area yield Tg Tg t ha Difference : Yield potential of IR8 was 9-10 t ha : Yield potential of IR72 is 9-10 t ha -1 Peng et al (1999) Crop Science 39,1552

5 Radiation use efficiency Biomass produced per unit radiation intercepted or absorbed Bambara groundnut 2006 Accumulated AG Dry weight Cumulative intercepted radiation Vegetative growth is proportional to intercepted radiation (Monteith 1977) RUE is critical in situations where biomass production is limiting yield.

6 Radiation use efficiency as a target for yield potential improvement Radiation Max. Grain Yield (t ha -1 ) Conversion Factor Tropics 110d Temperate (g dry matter MJ -1 ) 2.2 (rice) 10.0 (12.3) (wheat) (maize) Mitchell, Sheehy, Woodward (1998) IRRI discussion paper 32

7 Radiation use efficiency g DM MJ -1 intercepted PAR Mitchell et al (1998) Growth stage Above ground and below ground Absorbed radiation or intercepted radiation?

8 Radiation use efficiency Why does this ceiling (12.5 t ha -1 ) occur for tropical rice? Combination of leaf and canopy factors 15 t ha -1 impossible with current C3 photosynthesis Is rice efficient at capturing light energy and converting it into biomass? What are the routes forward for improvement of radiation use efficiency?

9 Leaf factors Eliminating photorespiration in tropical rice would improve RUE by 31 % Rice with C4 characteristics (IRRI priority) Kranz anatomy or single cell? Rubisco engineering Improvement of photosynthetic capacity Rice already has one of the highest of any C3 species (30-40 μmol CO 2 m -2 s -1 ) Improvement of dynamic responses of photosynthesis

10 Diurnal variation in light-saturated photosynthesis 60 days CO 2 Assimilation(μmols m -2 s -1 ) g (mols m -2 s -1 ) Time of day (hours) Time of day (hours) Mid-day depression of photosynthesis (light-saturated photosynthetic rate) Dry season, optimal conditions (irrigated, fertilised etc) Murchie et al (1999) Plant Physiology, 119,

11 Mid-day depression of photosynthesis in five cultivars of rice at two locations in the Philippines Photosynthesis (μmol CO 2 m -2 s -1 ) Light intensity (μmol m -2 s -1 ) Causes: Stomatal closure due to e.g. high vapour pressure deficit Photoinhibitory damage / down-regulation of light reactions Carbohydrate accumulation and feedback

12 Radiation capture and use in rice : leaf and canopy processes 1000 μmol m -2 s Rate of Excitation in leaf or canopy PPFD Un-used excitation Rate of Photosynthesis in leaf or canopy Used excitation Time of Day (hrs) Light Intensity

13 Light-saturation and photoinhibition of photosynthesis in the field φpsii Fv/Fm Time of day (hrs) Murchie et al (1999) Plant Physiology, 119,

14 Can the slow recovery of φco 2 affect canopy photosynthesis? photosynthesis Photoinhibition (slow recovering φco 2 ) light intensity Modelling using ray-tracing algorithms at a temperature of 30 o C predicts a reduction in canopy photosynthesis of 17 %. (Zhu, Ort, Whitmarsh, Long (2004), Journal of Experimental Botany 55, )

15 Current approaches 1. Canopy level assessment using transgenic rice. Slow recovery of φco 2 ( photoinhibition ) and resilience to rapid temperature alterations Collaboration with Peter Horton and Syngenta 2. Screening of IR64 deletion mutant collection for altered photosynthetic properties. 3. Analysis of photosynthesis in historical IRRI cultivars

16 Rice transformants Arabidopsis ChyB Rice PsbS Rice Lhcb1 Rice Pgr5 Induced on response to high light treatment microarray studies RNAi rice ChyB RNAi rice PsbS RNAi rice Lhcb1 RNAi rice Pgr5

17 Manipulating light-harvesting and photoprotection in rice ChyB β-carotene Xanthophyll cycle pool Zeaxanthin Protection of membrane lipids NPQ PsbS Energy dissipation photoinhibition Lowered φco 2

18 Dynamic light use efficiency: the genes involved PsbS 22 kda thylakoid protein. A key regulator in the switch between light harvesting and the dissipation of excess (harmful) energy. Light harvesting state PsbS Dissipative state (reduced φco 2 ) Its not just a switch! The amount of dissipation and the kinetics of formation and relaxation are determined quantitatively by the level of PsbS protein.

19 1. Empirical determination of the effect of energy dissipation within rice canopies. irradiance depth 2. Manipulation of the dissipative state using rice plants with varying PsbS and ChyB levels and measure the effects on canopy photosynthesis (modelled and measured) hrs 3. The role of fluctuating and constant irradiance levels (A.thaliana).

20 Davison et al, Nature (2000) Overexpression of β-carotene hydroxylase (ChyB) in Arabidopsis thaliana β- carotene Violaxanthin LL ML LL ML LL ML LL ML C24 ChyB

21 Overexpression of ChyB in A.thaliana confers higher resistance to high temperature and high irradiance Multiple stress treatment : 14 days at 1000 μmol m -2 s -1, 35 o C / 18 o C (day / night) ChyB overexpressors WT

22 Overexpression of ChyB in A.thaliana confers higher resistance to low temperature and high irradiance schyb 8.31 schyb 8.29 WT Matt Johnson (Sheffield), Michel Havaux (Cadarache)

23 Luminescence imaging of lipid peroxidation in vivo Matt Johnson (Sheffield), Michel Havaux (Cadarache)

24 10 out of 14 lines show elevated (max x2) levels of violaxanthin compared to expected wt levels Work to date 14 lines of rice transformed with catbch (Arabidopsis ChyB) grown under typical rice conditions Analysed by HPLC for changes in violaxanthin/neoxanthin ratio PCR analysis for presence of selectable marker gene

25 Carotenoid composition of transformed rice Car/chl (rel) B-car lutein neoxanth XC Carotenoid OE ChyB wt RNAi ChyB

26 Screening of the IR64 deletion mutant collection Forward screening of rice mutant collections is difficult for practical reasons. The IR64 deletion mutant collection at IRRI has 50,000 independent lines at the M4 stage. We have identified 1300 lines from the iris.irri.org database which have altered leaf shape. We are screening these for a number of characters: leaf thickness leaf area mesophyll cell size and arrangement chloroplast number and size

27 IRRI has released over 40 cultivars since 1966 Pmax (μmol CO2 m -2 s -1 ) stomatal condictance (mol H20 m -2 s -1 ) Peng et al (1999) Crop Science 39,1552) IR8 IR20 IR22 IR40 IR42 IR45 IR54 IR68 IR72 NPT PSBRC2

28 Underlying trends in historical IRRI cultivars? s.s. -significant to 5 % l n.s. - not significant Pmax s.s. n.s. s.s. n.s Total Chlorophyll qp s.s. n.s. s.s. n.s Rubisco stomatal conductance s.s n.s. s.s. Year of Cultivar Release n.s Total protein

29 Acknowledgements IRRI Uni. of Sheffield ChyB Work Shaobing Peng Yizhu Chen John Sheehy Jianchang Yang Peter Horton Stella Hubbart Matt Johnson Sveta Solovieva Tong Zhu Paul Davison, Neil Hunter (Sheffield), M.Havaux (Cadarache)