Plant Molecular Biology 16: 797-805, 1991. © 1991 Kluwer Academic Publishers. Printed in Belgium. 797 Differential expression of -amylase genes in germinating rice and barley seeds Erik E. Karrer, James C. Litts and Raymond L. Rodriguez* The Department of Genetics, University of California at Davis, Davis, CA 95616, USA (*author for correspondence) Received 21 May 1990; accepted 3 January 1991 Key words: alevrone, embryo, multigene family, northern blotting, intact germinating seeds Abstract Steady-state levels ofmRNA from individual a-amylase genes were measured in the embryo and aleurone tissues office (Oryza sativa) and two varieties of barley (Hordeum vulgare L. cv. Himalaya and cv. Klages) during germination. Each member of the c~-amylase multigene families office and barley was differentially expressed in each tissue. In rice, ct-amylase genes displayed tissue-specific expression in which genes RAmy3B, RAmy3C, and RAmy3E were preferentially expressed in the aleurone layer, genes RAmylA, RAmylB and RAmy3D were expressed in both the embryo and aleurone, and genes RAmy3A and RAmy2A were not expressed in either tissue. Whenever two or more genes were expressed in any tissue, the rate of mRNA accumulation from each gene was unique. In contrast to rice, barley a-amylase gene expression was not tissue-specific. Messenger RNAs encoding low- and high-pI or-amylase isozymes were detectable in both the embryo and aleurone and accumulated at different rates in each tissue. In particular, peak levels of mRNA encoding high-pI a-amylases always preceded those encoding low-pI a-amylases. Two distinct differences in a-amylase gene expression were observed between the two barley varieties. Levels of high-pI a-amylase mRNA peaked two days earlier in Klages embryos than in Himalaya embryos. Throughout six days of germination, Klages produced three times as much high-pI a-amylase mRNA and nearly four times as much low-pI a-amylase mRNA than the slower-germinating Himalaya variety. Introduction The hydrolytic enzyme a-amylase (EC 3.2.1.1) acts during the course of cereal germination to convert the starchy endosperm of the seed into nutrients that support the growing seedling [ 1, 4, 11 ]. Alpha-amylase gene expression is regu- lated at the level of transcription by the positive action of gibberellic acid (GA) and the negative action of abscisic acid (ABA) [15]. In cereals, total a-amylase activity is due to the combined action of separate isozymes encoded by multigene families. Rice or-amylases consist of four distinct isozymes [7] although two cDNA clones [22] and thirty genomic clones [14] have been iso- lated. An analysis of these genomic clones revealed ten distinct genes that fall into five hybridization groups [ 14]. DNA sequence analy- sis has allowed these genes to be consolidated into three subfamilies [13]. The relationship