Previously characterized Arabidopsis gl3 mutants have trichomes that are smaller, less branched and undergo fewer rounds of endoreplication than wild-type trichomes. A new gl3 mutant, called gl3-sst, has oddly shaped trichomes that over expand during early development, undergo more endoreduplication and that have a striking nuclear morphology. The mutant nuclei consist of many interconnected lobes; however, only a single set of polytenelike chromosomes reside in the mutant nuclei. The predicted gl3-sst polypeptide has a Leu to Phe substitution (codon 78) within a region responsible for protein-protein interaction. Yeast interaction assays comparing GL3 with gl3-sst proteins show that the mutant protein interaction with GL1 and TTG1 is decreased by 75% and 50%, respectively, but there is no difference in its interaction with TRY.Furthermore, TRY has the ability to prevent the GL1 GL3 interaction and the GL1 gl3-sst interaction is even more sensitive to TRY. Analysis of plants expressing functional GFP-tagged versions of GL1, GL3 and TRY show that the proteins are localized in trichome nuclei. These results have been used to model trichome initiation in terms of protein interactions and threshold levels of activator complex.Supplemental data available online

SummaryA screen of activation-tagged Arabidopsis lines resulted in the identification of At1g01380, which encodes a small R3 single repeat MYB gene, as a negative regulator of trichome initiation. Plants that overexpress this gene have fewer trichomes. The gene is closely related to the previously identified negative regulator TRY, and has a similar pattern of expression as TRY in developing leaves. As previously shown for TRY, At1g01380 protein can inhibit the interaction between the positive trichome regulators GL1 and GL3, and likely limits trichome initiation via this inhibition. While TRY and At1g01380 are closely related, they are not completely functionally equivalent. When placed under the transcriptional control of the TRY promoter, At1g01380 can only partially rescue the try mutant. Interestingly, Atg01380 is highly expressed in gl3-sst trichomes, while TRY expression is greatly reduced. The mutation in gl3-sst causes a reduced interaction between the GL1 and GL3 proteins and results in fewer leaf trichomes that develop in clusters. The differential expression of TRY and At1g01380 in this mutant can be used to explain how its altered trichome pattern in gl2-sst is generated.

Propionic acidemia (PA) is a recessive genetic disease that results in an inability to metabolize certain amino acids and odd-chain fatty acids. Current treatment involves restricting consumption of these substrates or liver transplantation. Deletion of the Pcca gene in mice mimics the most severe forms of the human disease. Pcca(-) mice die within 36 hours of birth, making it difficult to test intravenous systemic therapies in them. We generated an adult hypomorphic model of PA in Pcca(-) mice using a transgene bearing an A138T mutant of the human PCCA protein. Pcca(-/-)(A138T) mice have 2% of wild-type PCC activity, survive to adulthood, and have elevations in propionyl-carnitine, methylcitrate, glycine, alanine, lysine, ammonia, and markers associated with cardiomyopathy similar to those in patients with PA. This adult model allowed gene therapy testing by intravenous injection with adenovirus serotype 5 (Ad5) and adeno-associated virus 2/8 (AAV8) vectors. Ad5-mediated more rapid increases in PCCA protein and propionyl-CoA carboxylase (PCC) activity in the liver than AAV8 and both vectors reduced propionylcarnitine and methylcitrate levels. Phenotypic correction was transient with first generation Ad whereas AAV8-mediated long-lasting effects. These data suggest that this PA model may be a useful platform for optimizing systemic intravenous therapies for PA.

No abstract