Hormonal regulation, processing, and secretion of cysteine proteinases in barley aleurone layers

Genes That Mediate Starch Metabolism in Developing and Germinated Barley Grain

Starch is synthesized in the endosperm of developing barley grain, where it functions as the primary source of stored carbohydrate. In germinated grain these starch reserves are hydrolyzed to small oligosaccharides and glucose, which are transported to the embryo to support the growth of the developing seedling. Some of the mobilized glucose is transiently stored as starch in the scutellum of germinated grain. These processes are crucial for early seedling vigor, which is a key determinant of crop productivity and global food security. Several starch synthases (SS), starch-branching enzymes (SBEs), and starch debranching enzymes (isoamylases, ISA), together with a limit dextrinase (LD), have been implicated in starch synthesis from nucleotide-sugar precursors. Starch synthesis occurs both in the developing endosperm and in the scutellum of germinated grain. For the complete depolymerization of starch to glucose, α-amylase (Amy), β-amylase (Bmy), isoamylase (ISA), limit dextrinase (LD), and α-glucosidase (AGL) are required. Most of these enzymes are encoded by gene families of up to 10 or more members. Here RNA-seq transcription data from isolated tissues of intact developing and germinated barley grain have allowed us to identify the most important, specific gene family members for each of these processes in vivo and, at the same time, we have defined in detail the spatio-temporal coordination of gene expression in different tissues of the grain. A transcript dataset for 81,280 genes is publicly available as a resource for investigations into other cellular and biochemical processes that occur in the developing grain from 6 days after pollination.

Quantitative Proteomics Analysis of Barley-Based Liquid Feed and the Effect of Protease Inhibitors and NADPH-Dependent Thioredoxin Reductase/Thioredoxin (NTR/Trx) System

Liquid feeding strategies have been devised with the aim of enhancing grain nutrient availability for livestock. It is characterized by a steeping/soaking period that softens the grains and initiates mobilization of seed storage reserves. The present study uses 2D gel-based proteomics to investigate the role of proteolysis and reduction by thioredoxins over a 48 h steeping period by monitoring protein abundance dynamics in barley-based liquid feed samples supplemented with either protease inhibitors or NADPH-dependent thioredoxin reductase/thioredoxin (NTR/Trx). Several full-length storage proteins were only identified in the water-extractable fraction of feed containing protease inhibitors, illustrating significant inhibition of proteolytic activities arising during the steeping period. Application of functional NTR/Trx to liquid feed reductively increased the solubility of known and potentially new Trx-target proteins, e.g., outer membrane protein X, and their susceptibility to proteolysis. Thus, the NTR/Trx system exhibits important potential as a feed additive to enhance nutrient digestibility in monogastric animals.

Detection of the isoenzymes of wheat grain proteinase A

A new method for the purification of wheat cysteine proteinase A which plays a key role in the mobilization of seed storage proteins during germination has been developed. It consists of (NH4)2SO4 fractionation, gel filtration, and both ion-exchange and hydrophobic chromatography. Constancy of the specific activity of chromatographic fractions and their SDS-electrophoretic pattern indicates the homogeneity of the final enzyme preparation. However, electrophoresis in nondenaturing conditions revealed three protein bands of similar intensity, each showing proteolytic activity. The N-terminal sequences of all three electrophoretic components are identical. They are also identical to a segment of the amino acid sequence deduced from one of several cDNA clones derived from closely related, but non-identical mRNAs that accumulate in the aleurone layer of gibberellic acid-treated wheat. It is very likely that the three electrophoretic components found are isoenzymes encoded by cDNA clones described by these authors.