Difference between revisions of "IC4R005-Phenomics-2009-11089458"

Revision as of 15:55, 28 July 2016

There is now strong evidence that yield potential in rice (Oryza sativa L.) is becoming limited by ‘source’ capacity, i.e. photosynthetic capacity or efficiency, and hence the ability to fill the large number of grain ‘sinks’ produced in modern varieties. One solution to this problem is to introduce a more efficient, higher capacity photosynthetic mechanism to rice, theC4 pathway.Amajor challenge is identifying and engineering the genes necessary to installC4 photosynthesis in rice. Recently, an international research consortium was established to achieve this aim. Central to the aims of this project is phenotyping large populations of rice and sorghum (Sorghum bicolor L.) mutants for ‘C4-ness’ to identifyC3 plants that have acquired C4 characteristics or revertant C4 plants that have lost them. This paper describes a variety of plant phenomics approaches to identify these plants and the genes responsible, based on the detailed physiological knowledge of C4 photosynthesis.

Genetic modification of rice to have C4 traits (functioning as a C3–C4 intermediate or C4 plant) is a challenging goal, requiring both anatomical and biochemical specialisation and compartmentation within chlorenchyma cells (Fig. 1). In C4 plants, spatial separation of the capture of atmospheric CO2 from its delivery to Rubisco is required. It has been suggested that evolution of C4 has occurred multiple times by a stepwise progression of structural and biochemical changes that were induced by CO2-limiting conditions (Sage 2004 and references therein). The occurrence of ‘intermediates’ between C3 and C4 plants has provided a basis for suggesting how C4 may have evolved from C3, to intermediates that reduce photorespiration without a C4 cycle, to intermediates having a partially functioning C4 cycle, to full development of C4 (Fig. 2).

Fig. 1. A simplified scheme of the C4 pathway (adapted from von Caemmerer 2000).

Fig. 2. A simplified scheme of the C3–C4 intermediate photosynthetic pathway (adapted from von Caemmerer 2000).

A useful high throughput diagnostic tool that can be employed both to discover C4 anatomical revertants and C4-like rice anatomical mutants is to screen for vein spacing, easily achieved with a hand-held microscope and in more detail using laser confocal microscopy (Figs 3, 4). Figure 3a, b illustrate a high throughput technique to estimate vein spacing in intact C3 and C4 leaves using low magnification light micrographs of live rice and maize leaves, respectively, imaged from above the epidermis. Figure 3c, d shows higher resolution measurements of fluorescent dyes in transverse sections of rice and maize leaves imaged using epifluorescence microscopy, which clearly illustrate the number of cells separating the vascular bundles by outlining cells.

CSIRO Plant Industry and High Resolution Plant Phenomics Centre, GPO Box 1600, Canberra, ACT 2601, Australia.
Research School of Biology, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.

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 [[File:IC4R005-Phenomics-2009-11089458-f2.png |center |thumb |800px |'''Fig. 2. A simplified scheme of the C3–C4 intermediate photosynthetic pathway (adapted from von Caemmerer 2000).''']]
+* A useful high throughput diagnostic tool that can be employed both to discover C4 anatomical revertants and C4-like rice anatomical mutants is to screen for vein spacing, easily achieved with a hand-held microscope and in more detail using laser confocal microscopy (Figs 3, 4). Figure 3a, b illustrate a high throughput technique to estimate vein spacing in intact C3 and C4 leaves using low magnification light micrographs of live rice and maize leaves, respectively, imaged from above the epidermis. Figure 3c, d shows higher resolution measurements of fluorescent dyes in transverse sections of rice and maize leaves imaged using epifluorescence microscopy, which clearly illustrate the number of cells separating the vascular bundles by outlining cells.
 ==Labs working on this Project==