Poster: Hormones

Abs # 643: Global expression patterns in rice and barley aleurone provide clues to hormone signaling and metabolic regulation.

Presenter:	Jones, Russell , Rjones@nature.berkeley.edu
Authors	Jones, Russell  (A)   Hwang, Yong-sic  (A)   Holappa, Lynn  (A)   Bethke, Paul  (A)   Magnani, Enrico  (A)   Zhu, Tong  (B)
Affiliations:	(A): University of California (B): Syngenta, RTP

Activities in the aleurone layer of rice and barley are hormonally controlled. The transcription of genes for secreted hydrolases, the mobilization of protein and lipid reserves, and the programmed death of aleurone cells are initiated by gibberellins (GA) and inhibited by abscisic acid (ABA). In order to uncover novel aspects of transcriptional regulation and metabolic control we have examined transcript profiles of rice and barley aleurone treated with GA or ABA. Of the ~20,000 genes represented on the Syngenta oligonucleotide microarray, ~1,500 are hormonally regulated in both rice and barley. Surprisingly, ABA increases the transcript abundance for as many genes as GA, and comparable numbers of genes are down- and up-regulated by GA. Self organizing maps were used to describe the data and to show that genes with similar function are often coordinately regulated. This analysis also shows that genes regulated specifically by ABA are rare. An examination of key metabolic pathways shows that specific enzymes involved in lipid and protein breakdown are up-regulated by GA. These include lipase, acyl CoA oxidase and cysteine proteases. In contrast, oleosins and protease inhibitors are up-regulated by ABA. ABA also up-regulates a 1-carbon metabolic pathway centered on S-adenosyl methionine. Putative GA signaling components have been identified and one of these, a GA-induced calcineurin B-like gene, has been cloned. To further dissect the GA signaling pathway we compared expression patterns in wild type and d1 mutant rice aleurone. The d1 mutant lacks the alpha subunit of heterotrimeric G-protein and has a dwarf phenotype. Comparisons between transcript abundance at low and high concentrations of GA show that D1 affects the sensitivity of transcription to GA.