Euphytica 119: 49–54, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 49 Molecular genetic studies on processing traits of wheat flour R. Appels, P. Gras, B.C. Clarke, R. Anderssen, I. Wesley & F. B´ ek´ es CSIRO Divisions of Plant Industry and Mathematical and Information Sciences Canberra, ACT, Australia 2601 Key words: Dough development, glutenins, seed storage, wheat flour Abstract Advances in the genetic mapping of wheat, the molecular interpretation of flour processing traits and large-scale sequencing of genes expressed in endosperm tissue are currently converging to define the genes that under-pin key quality traits. In order to achieve this, accurate definitions of a phenotype such as dough extensibility are essential and in this paper a molecular/genetic analysis of this trait is presented. Studies carried out on the small- scale Mixograph have provided the data to indicate that the mixing action in this system develops the dough through multiple elongate-rupture-relax cycles of the flour/water mixture. The measurement can be used to define a variable we refer to as ‘M-extensibility’, a measure very closely related to the traditional extensibility measurement and most likely a sub-component of this ‘classical’ assessment. Analyses based on molecular genetic maps have shown that both LMW and HMW glutenin loci most likely account for significant variation in M-extensibility. In addition, it is evident that genes on chromosome 2 also contribute and work is in progress to characterize these genes. The possibility will be discussed that new seed storage protein genes being discovered from the analysis of 5000 cDNA’s from endosperm tissue (8–12 days post anthesis) have a role to play in M-extensibility. Introduction The functional properties of flour reflect the devel- opment of the grain and the manner in which struc- tures such as starch granules and protein bodies have accumulated during the course of grain maturation. Classical studies have characterized endosperm devel- opment at the level of cell structure (Simmonds & O’Brien, 1981). Within endosperm cells, the structure and biosynthesis of starch granules in wheat is now also well understood (Morell et al, this volume) and comprises 60–70% of the final weight of the grain. Starch is deposited as insoluble granules in amylo- plasts (Briarty et al., 1979), specialised starch biosyn- thetic organelles derived from the same proplastids as chloroplasts, but containing no photosynthetic appar- atus. Although the precise molecular events that occur at the initiation of the starch granule remain obscure, it is clear that it occurs in two stages. One stage is in phase 1 of endosperm development when the large ‘A’ granules are initiated, and a second in phase 2 of endosperm development, when a much more pro- lific, period of granule initiation occurs. The second stage of granule initiation leads to the development of the small ‘B’ granule populations. A third burst of ‘C’ granule initiation has also been observed in wheat (Bechtel et al., 1990). The deposition of proteins into protein bodies (re- viewed in Shewry, 1996) begins in the period 6–10 days post anthesis of endosperm development. Com- pared to the information available for starch granules, the internal structure of the protein matrix still requires detailed definition. The addition of water to dry flour (J. Bernardin, unpublished observations) and light mi- croscopic observations on the wetting process show very long strands of polymeric material, with starch granules loosely attached, streaming away from the flour mass. These observations imply that during en- dosperm maturation the protein bodies accumulate at least some proteins in very large polymers, visible at relatively low magnification, when flour is rehydrated. Cereal chemistry has provided a detailed description of the components of flour as well as some indica- tion of the polymeric structures formed during flour