2010 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.
CONTROL OF MAIZE LEAF DIFFERENTIATION AND BIOMASS ACCUMULATION BY THE SPL TRANSCRIPTION FACTOR FAMILY
Of the seven SPL genes that are responsible for the Cg1 phenotype, loss of function mutations exist for six. In collaboration with UC Berkeley, Cold Spring Harbor, and Pioneer scientists, we recently published on the knockout phenotype of TC305894, now known as tasselsheath4 (tsh4). tsh4 is a repressor of leaf initiation within the floral phase, thus explaining why Cg1 mutations continuously initiate leaves within the inflorescence. Overall, these results suggest that maize Cg1 mutants possess increased biomass through excess leaf initation as a result of loss of SPL leaf repressors.
In order to demonstrate the usefulness of the Cg1 microRNA gene in enhancing biofuel properties, we have begun several collaborations to put the maize Cg1 gene into several potential biofuel crop plants and assay their digestibility properties. These transformed crops include Brachypodium, a model grass system, poplar, a model tree system, and switchgrass, a biofuel crop already in use. Cg1 transformants in all species display similar phenotypes, displaying increased biomass due to derepression of axillary buds, as well as increased leaf initiation. More detailed analysis has been done with the switchgrass tranformants. Analysis of the MIR spectra of this switchgrass biomass was done for us by the Joint Bioenergy Institue in Emeryville. Significant differences in lignin and cellulose levels were noticed in several greenhouse grown transformants. We recently received a field permit to grow these transformants at U.C. Berkeley and will repeat this analysis, as well as several other assays, to determine if this biomass is in fact superior to untransformed switchgrass.
Chuck, G., Whipple, C., Jackson, D., Hake, S.C. 2010. The maize SBP-box transcription factor encoded by tasselsheath4 regulates bract development and the establishment of meristem boundaries. Development. 137(8):1243-1250.