Abstract
All grass leaves are strap-shaped with a series of parallel veins running from base to tip, but the distance between each pair of veins, and the cell-types that develop between them, differs depending on whether the plant performs C3 or C4 photosynthesis. As part of a multinational effort to introduce C4 traits into rice to boost crop yield, candidate regulators of C4 leaf anatomy were previously identified through an analysis of maize leaf transcriptomes. Here we tested the potential of 60 of those candidate genes to alter leaf anatomy in rice. In each case, transgenic rice lines were generated in which the maize gene was constitutively expressed. Lines grouped into three phenotypic classes: (1) indistinguishable from wild-type; (2) aberrant shoot and/or root growth indicating possible perturbations to hormone homeostasis; and (3) altered secondary cell wall formation. One of the genes in class 3 defines a novel monocot-specific family. None of the genes were individually sufficient to induce C4-like vein patterning or cell-type differentiation in rice. A better understanding of gene function in C4 plants is now needed to inform more sophisticated engineering attempts to alter leaf anatomy in C3 plants.
Highlights
More than 25 genes in this class encoded transcription factors which were expected to alter the expression of a number of downstream genes
The lack of phenotypic perturbation observed suggests either that plant developmental processes are buffered against changes in these particular transcriptional networks or that the maize genes cannot activate downstream targets in rice
One of the genes in this class is ZmSCARECROW1, a gene which when mutated in maize causes subtle defects in Kranz anatomy[1]
Summary
Peng Wang 1, Shanta Karki[2,8], Akshaya K. We tested the potential of 60 of those candidate genes to alter leaf anatomy in rice. Genes that regulate developmental processes have traditionally been identified through mutant screens for phenotypic defects. This approach has been enormously powerful for the elucidation of genetic pathways that underpin a large number of developmental mechanisms in model organisms across the phylogenetic range. Whereas C3 leaves develop 5–20 M cells between each pair of veins, C4 leaves develop concentric wreaths of BS and M cells around each vein (V) so that each pair of veins is normally separated by four cells in a V-BS-M-M-BS-V unit Correspondence and requests for materials should be addressed to J.A.L
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