Poster: Regulation of gene expression

Abs # 747: Maintenance of a functional proteome.

Presenter:	Xu, Qilong , qxu2@uky.edu
Authors	Xu, Qilong  (A)   Villa, Sarah T. (B)   Belcastro, Marissa  (A)   Dinkins, Randy  (A)   Clarke, Steven  (B)   Downie, Bruce  (A)
Affiliations:	(A): University of Kentucky (B): University of California, Los Angeles

Conversion of aspartate and asparagine residues to isoaspartate is a prevalent covalent protein modification in cells. These deleterious conversions can lead to impaired enzyme function and the recognition, tagging, and destruction of the altered peptides, requiring that they be resynthesized de novo. Fortunately, protein repair processes exist that mitigate the injurious effects of aging. Protein L-isoaspartyl methyltransferases (PIMT) iteratively methylate abnormal isoaspartyl residues leading to conversion to L-aspartate. The model plant Arabidopsis thaliana is unique among eukaryotes studied to date in that it possesses two genes encoding PIMT. The second PIMT exhibits a complex transcriptional control involving different transcriptional start sites and 5'- and 3'-alternative splice site selection in the first intron. Varying the transcriptional start site results in alternative targeting of the PIMT2 proteins thus produced to: 1) the nucleus, 2) the mitochondria and plastids, or 3) the cytoplasm. Multiplex RT-PCR was used to establish PIMT1 and PIMT2 transcript presence and abundance, relative to β-TUBULIN, in various tissues and under a variety of stresses imposed on seeds and seedlings. PIMT1 transcript is constitutively present but can increase, along with PIMT2, in developing seeds presumably in response to increasing endogenous ABA. Transcript from PIMT2 also increases in establishing seedlings due to exogenous ABA or applied stress presumably through an ABA-dependent pathway. Furthermore, Cleaved Amplified Polymorphic Sequence analysis of the PIMT2 amplicons has shown that the ratio among the splicing variants alters upon ABA application, implicating a role for the spliceosome in orchestrating the plant's response to stress.