Location: Plant Gene Expression Center2011 Annual Report
1a. Objectives (from AD-416)
We propose to identify genes that regulate cell walls in maize leaves in order to improve saccharification in grass species.
1b. Approach (from AD-416)
We cloned the Corngrass gene in maize that keeps the plant in a juvenile state. We determined that it is a microRNA that regulates SPL transcription factors. These transcription factors are thus responsible for the shift from juvenile to adult leaves and for the production of prop roots in maize. We will determine the genes that are regulated by each SPL gene using reverse genetics and a combination of biochemistry and histology. Documents Reimbursable with DOE. Log 34608. Formerly 5335-21000-028-05R (11/10).
3. Progress Report
MicroRNAs regulate genes by targeting degradation of their transcripts or proteins. Corngrass (Cg1) is a microRNA that targets Squamosa Promoter bind protein Like (SPL) genes. Since the target genes of Cg1 are conserved in many plant species, we hypothesized that it should be possible to transfer the biofuel properties of the maize Cg1 mutant into any crop of choice simply by overexpressing the Cg1 cDNA and downregulating its targets. This was tested in the model dicot Arabidopsis, the model tree system Populus in collaboration with scientists at Purude, the model grass system Brachypodium and the biofuel crop plant Panicum virgatum (switchgrass) in collaboration with ARS scientists in the Western Region Research Center. These lines were all confirmed as having reduced levels of SPL transcription factors. Increased vegetative branching and leaf initiation were seen in all transgenic lines, demonstrating the utility of this approach. In addition, histological analysis of these lines revealed numerous differences in cell number, morphology and identity. In general, these leaves had fewer cell layers, reduced leaf thickness, fewer hypodermal schlerenchyma cells (lignified support cells) and juvenile waxes, properties that mimic the juvenile phenotypes found in maize Cg1. The poplar transformants displayed up to a 30% reduction of lignin. We grew the switchgrass in field trials and found that they 1) never flowered, 2) had increased numbers of stems, 3) had increased levels of starch. The increase in starch improved their saccharification. Future experiments are aimed at expressing Cg1 with different promoters that are not expressed in roots.