322:	ABA regulates the posttranslational processing and subcellular localization of aleurain in barley aleurone.

Authors:	Fath , Angelika(A)Bethke , Paul, C.(A)Zhang, Juan(A)Jennifer, Lonsdale, E.(A)Jones, Russell, L.(A)
Affiliations:	(A): Department of Plant and Microbial Biology, University of California, Berkeley CA 94720
Presenter:	Fath , Angelika , afath@nature.berkeley.edu

Abscisic acid (ABA) inhibits many gibberellin (GA)-induced processes in the barley aleurone, including the synthesis and secretion of hydrolases and cell death. ABA has a profound effect on the synthesis, processing and localization of the cysteine protease aleurain. Aleurain, a homologue of the mammalian lysosomal enzyme cathepsin H, is synthesized as a 42 kD precursor (proaleurain) and is processed to 32 kD mature aleurain. The accumulation of mature aleurain in aleurone cells is prevented by ABA. RNA blotting showed that proaleurain mRNA accumulated in aleurone layers without hormone treatment and its level was weakly upregulated by GA, but strongly down-regulated by ABA. Protein blotting showed that proaleurain was processed to aleurain in the absence of added hormones or in GA-treated cells, but only proaleurain accumulated in cells incubated in ABA. Immunocytochemistry and protein blotting of isolated organelle fractions was used to localize proaleurain and aleurain. These approaches showed that proaleurain was located in small organelles (2 um, diameter) which did not immunolabel with a-TIP and were distinct from protein storage vacuoles and secondary vacuoles. Mature aleurain, on the other hand, was located in protein storage vacuoles. We propose that GA promotes the post-translational processing and relocalization of aleurain in barley aleurone and that ABA prevents these processes.