Abstract
A high leaf vein density is both an essential feature of C4 photosynthesis and a foundation trait to C4 evolution, ensuring the optimal proportion and proximity of mesophyll and bundle sheath cells for permitting the rapid exchange of photosynthates. Two rice mutant populations, a deletion mutant library with a cv. IR64 background (12,470 lines) and a T-DNA insertion mutant library with a cv. Tainung 67 background (10,830 lines), were screened for increases in vein density. A high throughput method with handheld microscopes was developed and its accuracy was supported by more rigorous microscopy analysis. Eight lines with significantly increased leaf vein densities were identified to be used as genetic stock for the global C4 Rice Consortium. The candidate population was shown to include both shared and independent mutations and so more than one gene controlled the high vein density phenotype. The high vein density trait was found to be linked to a narrow leaf width trait but the linkage was incomplete. The more genetically robust narrow leaf width trait was proposed to be used as a reliable phenotypic marker for finding high vein density variants in rice in future screens.
Highlights
The yield potential of rice (Oryza sativa L.) needs to be increased by at least 50% by 2050 to support the burgeoning human population, which can only be underpinned by improvements in rates of biomass production [1]
We investigated the close link of leaf vein density with leaf width, which was found in the high vein density mutant lines that had narrow leaf widths in [23]
Vein density screening The primary genetic resource was the International Rice Research Institute (IRRI) IR64 deletion mutant population derived from a single IR64 plant, IR64-21 [13]
Summary
The yield potential of rice (Oryza sativa L.) needs to be increased by at least 50% by 2050 to support the burgeoning human population, which can only be underpinned by improvements in rates of biomass production [1]. C4 photosynthesis is characterized by a CO2 concentrating mechanism involving the coordination of metabolism in two cell types, the mesophyll and bundle sheath It results in the elimination or substantial reduction in photorespiration and an enhancement in the capacity and quantum yield of photosynthesis at high temperatures [2] [3] [4]. It is needed to ensure the optimal ratio of mesophyll and bundle sheath cells with close contact permitting the rapid exchange of photosynthates. This is achieved via ‘Kranz’ anatomy which typically shows a single or double layer of mesophyll cells enclosing bundle sheath cells in a concentric fashion. A possible source of study for identification of rice genes regulating traits relevant to C4, like high leaf vein density, is mutagenized populations
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