Poster: Protein Targeting & Vesicular Trafficking

Abs # 1195: The role of ADP-ribosylation factor in hormone-stimulated secretion in barley aleurone

Presenter:	MacCleery, Scott , sam324@psu.edu
Authors	MacCleery, Scott  (A)   McCubbin, Andrew  (B)   Gilroy, Simon  (A)
Affiliations:	(A): Penn State University (B): Washington State University

Cereal grain germination requires that a great amount of energy and nutrients be made available for the growing embryo, but also precise control over its timing. The aleurone layer of the grain enables this mobilization by synthesizing and secreting hydrolytic enzymes (primarily a-amylases) into the starchy endosperm of the grain, thus providing an ideal model of hormonal response and secretion. Fine control is maintained by the aleurone’s opposing responses to gibberellic acid (GA) and abscisic acid (ABA). ADP-ribosylation factors (ARFs) are members of a protein family that is potentially involved in both responses. ARFs are monomeric GTP-binding protein in the RAS 'superfamily' that have been shown to be involved in protein-trafficking/vesicle formation in yeast and animals. In plants, ARF has been shown to be involved in xylem formation, Golgi morphology in Arabidopsis mesophyll cells, and indirectly in embryonic positioning of an auxin efflux carrier in Arabidopsis embryos. We have found that ARFs are expressed in barley aleurone and the toxin brefeldin A (BFA), which inhibits ARF, reversibly reduces the amylase secretion from these cells implying a role in GA response. We have cloned an ARF from barley (HvARF) To test the functional similarity with those ARFs currently described we have successfully complimented a yeast ARF1 deletion mutant with HvARF. To further explore HvARFs role in barley aleurone we have constructed a dominant negative and dominant positive HvARFs (GTP-bound and GDP-bound) to test its effects on hormone stimulation and secretion. These mutants are being used to define HvARF’s role(s) in hormone stimulated secretion. This work was supported by the USDA and NSF.