Planta (1988)174:551 560 Planta 9 Springer-Verlag 1988 Hormonal regulation of gene expression in barley aleurone layers Induction and suppression of specific genes Randall C. Nolan* and Tuan-Hua David Ho ** Department of Biology and Plant Biology Program, Division of Biology and Biomedical Sciences, Washington University, St. Louis, MO 63130, USA Abstract. As part of our investigation of the mode of action of plant hormones in barley (Hordeum vulgate L.) aleurone layers, we have studied the expression of five identified and three unidentified mRNA species in the presence of exogenous gib- berellic acid (GA3) and abscisic acid. Three of the mRNAs are GA3-inducible, three are suppressed by GA3, and two are constitutive. The extent of the GA3 effect differs considerably for both induc- ible and suppressible mRNAs. For example, a ten- fold higher concentration of GA3 (10 -8 M) is re- quired for full induction of the high-pI group e- amylase mRNA than is required for the low-pI e-amylase mRNA (10-9 M). Temporal regulation of mRNA abundance also varies between the two e-amylase isoenzyme groups. The three GA3-sup- pressible mRNA species studied, alcohol dehy- drogenase (ADH1), a probable amylase and pro- tease inhibitor, and an unidentified barley mRNA species also varied in response to GA3. The ADH1 mRNA decreased drastically within 8 h of GA3 treatment, whereas the other two began to decrease in abundance only after 12-16 h of GA3 treatment. Abscisic-acid treatment counteracted the GA3 ef- fects for both the inducible and suppressible mRNA species. Comparison of e-amylase-mRNA levels and e-amylase-synthesis rates showed a strong correlation between the two parameters, the only exception being a lack of e-amylase synthesis in the presence of e-amylase mRNA at low GA3 concentrations. Therefore, the expression of e- amylase seems to be regulated primarily by its mRNA levels. * Present address: Department of Biology, Indiana University, Bloomington, IN 47401, USA ** To whom correspondence should be addressed Abbreviations:ABA = abscisic acid; ADH1 = alcohol dehy- drogenase 1; eDNA=copy DNA; GA3=gibberellic acid; PAPI = probable amylase/protease inhibitor Key words: Abscisic acid and gene expression - Aleurone - e-Amylase - Gene expression (barley aleurone) - Gibberellin and gene expression - Hor- deum (gene expression). Introduction Barley aleurone layers have provided a model sys- tem for the study of the regulation of gene expres- sion by plant hormones. Gibberellic acid (GA3), synthesized in the germinating barley embryo, dif- fuses to the aleurone layer cells, where it triggers the synthesis and secretion of several hydrolytic enzymes. These hydrolases then break down stor- age materials in the endosperm into smaller com- ponents, which are used by the seedling to main- tain growth until photosynthesis commences. In isolated aleurone layers, GA3 has been shown to induce synthesis of e-amylase isoenzymes (EC 3.2.1.1), proteases, nuclease (EC 3.1.30.2), fl- 1,3; 1,4-glucanases (EC 3.2.1.73), and other hydro- lases (Jacobsen and Higgins 1982; Callis and Ho 1983; Hammerton and Ho 1986; Brown and Ho 1986; Stuart et al. 1986). The mRNA for e-amy- lase, fl-1,3 ; 1,4-glucanase, and a putative thiol pro- tease, aleurain, have also been shown to be induced by GA3, (Rogers 1985; Muthukrishnan et al. 1983; Chandler et al. 1984; Stuart et al. 1986; Rogers et al. 1985). Jacobsen and Beach (1985) have dem- onstrated a tenfold stimulation of transcription of e-amylase genes by run-on transcription studies using nuclei from GA3-responsive aleurone proto- plasts. Abscisic acid (ABA) blocks this stimulation of e-amylase transcription. In fact, ABA has been found to antagonize GA3 action in all of the events investigated thus far in barley aleurone layers (Ho 1983).