We have demonstrated that expression of genes involved in starch and storage protein synthesis of the maize (Zea mays 1.) endosperm are coordinated. Genetic lesions altering synthetic events in one biosynthetic pathway affect expression of genes in both pathways. Initial studies focused on shrunken2 (sh2) and briffle2 (bf2) mutants because these genes encode subunits of the same enzyme, ADP-glucose pyrophosphorylase. Analysis of various sh2-and bf2-mutant alleles showed that the most severe mutations also conditioned the largest increase in transcripts. The analysis was extended by monitoring the transcripts of the genes, shrunken1 (shl, structural gene for Suc synthase), sh2, bf2, waxy1 (wxl, structural gene for starch synthase), and those of the large and small zeins in isogenic maize lines at 14, 22, and 30 d postpollination. Endosperms were wild type for all of these genes or contained shl-, sh2-, btl-, bt2-, opaque2 (02-), or amylose-extender7 (del-) dulll (dul-) wxl-mutations. Transcripts increased continually throughout kernel development in the mutants relative to the standard W64A used. Variation in the amount of SUC entering the developing seed also altered transcript amounts. The results indicate that starch and protein biosynthetic genes act in a concerted manner, and both are sensitive to mutationally induced differences.The maize (Zea mays L.) endosperm is a specialized tissue that provides a source of nutrients to the germinated embryo. The vast majority of carbon used in the early steps of seedling development is derived from starch and the storage proteins, the zeins. These storage products account for approximately 90% of the dry weight of a mature maize endosperm.Historically, mutants have provided the most insight into the pathways of starch and zein synthesis. Many endosperm mutations can be classified as affecting starch or zein biosynthesis. Mutations such as 02-, flou y2-, and 07-decrease zein content, and proteins in the other solubility classes increase in abundance (Mertz et al., 1964;Nelson et al., 1965;Ma and Nelson, 1975;Habben et al., 1993). 02 has been shown to encode a trans-acting regulatory protein involved in zein transcription (Schmidt et al., 1990). S and L zeins represent the 19-and 22-kD classes of zein polypeptides and an 02-mutation affects mainly the production of 22-kD zein proteins (Langridge et al., 1982).
Contribution from the Florida Agricultural Experiment Station Journal Series, No. R-03868.* Corresponding author; fax 1-904-392-6479.
3The majority of the enzymes known to be involved in the starch biosynthetic pathway follow similar developmental timing (Tsai et al., 1970). Ingle et al. (1965) found maximum endosperm sugar content at 22 dpp. This stage of development is also when the starch biosynthetic enzymes are most active (Tsai et al., 1970). Mutations in the genes shl (the structural gene for SUC synthase; Chourey and Nelson, 1976), btl (the structural gene for a membrane-bound, adenylate camer; Sullivan et al., 1991), and sh2 and bt2 (both structural genes ...