Review Pre-maturity a-amylase in wheat: The role of abscisic acid and gibberellins K.R. Kondhare a , A.D. Farrell b , P.S. Kettlewell c, * , P. Hedden d , J.M. Monaghan c a Indian Institute of Science Education and Research (IISER) Pune, Biology, Maharashtra 411008, India b The University of the West Indies, Department of Life Sciences, St. Augustine, Trinidad, West Indies c Harper Adams University, Department of Crop and Environment Sciences, Newport TF10 8NB, UK d Rothamsted Research, Department of Plant Biology and Crop Science, Harpenden AL5 2JQ, UK article info Article history: Received 30 January 2015 Received in revised form 12 March 2015 Accepted 15 March 2015 Available online 17 April 2015 Keywords: Abscisic acid Gibberellins Pre-maturity a-amylase Wheat grain abstract The occurrence of pre-maturity a-amylase (PMA) is a major cause of poor bread-making quality (low Hagberg Falling Number) in wheat grain. In susceptible genotypes, it involves the excessive accumulation of high isoelectric point (pI) a-amylase in mature grain prior to germination and in the absence of pre- harvest sprouting. Several factors regulate PMA formation in developing grain, including genotype, agronomy, and environmental conditions. In particular, a cold period during mid-grain development has been found to be a major stimulus for PMA induction. Although the factors affecting the PMA occurrence are well known, little is known about the molecular mechanism governing its induction. The plant hormones abscisic acid (ABA) and gibberellins (GAs) influence various aspects of grain development, and it has been suggested that PMA involves changes in the amount of these hormones or the sensitivity of the grain to these hormones. This review summarizes recent studies investigating the role of ABA and GAs in PMA induction and PMA occurrence. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Pre-maturity a-amylase (PMA) formation in susceptible geno- types involves an excessive synthesis of high isoelectric point (pI) a-amylase in the later stages of wheat grain ripening, prior to germination. This high level of a-amylase is retained in mature grain and renders it unsuitable for bread-making (Mares and Mrva, 2008). PMA appears to be the second major cause of a low Hagberg Falling Number (HFN), following pre-harvest sprouting (PHS) (Lunn et al., 2001a). PMA is also referred to as late maturity a-amylase or late maturity endosperm a-amylase (Lunn et al., 2001a). The occurrence of PMA is difficult to predict and difficult to detect as the PMA-affected grain retains a sound appearance. PMA has been reported in Australia, Canada, China, Germany, Japan, Mexico, South Africa, UK and USA (Mohler et al., 2014; Mares and Mrva, 2008). Most PMA studies have been carried out in Australia and in the UK and wheat breeders in many parts of the world are only just coming to the realization that it represents a source of low HFN in their germplasm. Several factors are involved in regulating PMA formation in developing grain, including genotype, agronomy, and environmental conditions (Barrero et al., 2013; Barnard and Smith, 2012; Farrell and Kettlewell, 2008, 2009; Mrva and Mares, 2006). Some genotypes are considered PMA-constitutive as they consis- tently produce affected grain, while in other genotypes the occur- rence of PMA is sporadic and influenced by growing conditions. In particular, a cold-shock applied approximately 26e30 days after anthesis (DAA) can induce PMA in susceptible genotypes. This has been termed the window of sensitivity for PMA induction (Farrell and Kettlewell, 2008; Mrva and Mares, 2001a). Thus, wheat geno- types can be divided into three categories: non-PMA, PMA-prone, or PMA-constitutive (Mares and Mrva, 2008). Abbreviations: ABA, abscisic acid; ABREs, ABA-responsive elements; CaM, calmodulin; DAA, days after anthesis; DELLA, growth repressor; DPA, dihy- drophaseic acid; GAs, gibberellins; GAi, gibberellin-insensitive; GAMYB, transcrip- tion factor for a-amylase promoter; GGPP, trans-geranylgeranyldiphosphate; GID1, GA-INSENSITIVE DWARF1; GA 3 , gibberellic acid (active GA produced by one branch of the biosynthetic pathway); HFN, Hagberg Falling Number; IPP, isopentenyl diphosphate; PA, phaseic acid; PB, paclobutrazol; pI, isoelectric point; PKABA1, ABA-inducible Ser/Thr protein kinase 1; PMA, pre-maturity a-amylase; PP2C, Group-A protein phosphatases 2C; PYL/PYR/RCAR, nuclear ABA receptor; QTL, quantitative trait locus; RH, relative humidity; Rht, reduced height genes; SnRK2, sucrose nonfermenting1-related protein kinases 2; UK, United Kingdom; USA, United States of America; 1B/1R, wheat-rye chromosome translocation where the short arm of the 1B chromosome in wheat is replaced by the short arm of the 1R chromosome from rye. * Corresponding author. Tel.: þ44 (0)1952 815299; fax: þ44 (0)1952 814783. E-mail address: pskettlewell@harper-adams.ac.uk (P.S. Kettlewell). Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs http://dx.doi.org/10.1016/j.jcs.2015.03.004 0733-5210/© 2015 Elsevier Ltd. All rights reserved. Journal of Cereal Science 63 (2015) 95e108