The plant seed with its reserves of starch, proteins and lipids constitutes the main feedstock for the human food supply chain. Two thirds of the calories consumed by humans can be traced back to cereals. Providing enzymes to modify plant macromolecules for smarter, more efficient and sustainable products is a key task in biotechnology and hydrolytic enzymes evolved in planta have enormous potential.
Phytases (myoinositol hexakisphosphate phosphohydrolase; EC 184.108.40.206 and EC 220.127.116.11) are phosphatases that initiate the sequential liberation of orthophosphate groups from phytate (myoinositol 1,2,3,4,5,6-hexakisphosphate). Phytases are of particular importance during seed germination, where they mobilize phosphate from phytate, the major reserve (~70%) of phosphorus in plant seeds. However, in mature ungerminated seeds and in the digestive tract of non-ruminant animals, there is often little or no phytase activity. When dry seeds are used for feed, this has a number of consequences. Digestible phosphate such a di-calcium phosphate (which is a limited resource) must be added to the animal feed to ensure the proper nutritional composition. The undigested phytate excreted in the manure in turn gives rise to concern since it contributes significantly to the environmental phosphate load. Finally, phytate is considered the single most important antinutritional factor for the bio-availability of minerals such as iron, calcium and zinc.
Plant seeds with a high phytase activity is considered an important means for improving phosphate and mineral bioavailability in feed and food. However, different plant species have developed various strategies for phytase-mediated degradation of phytate during germination. The cereals, barley (Hordeum vulgare), wheat (Triticum aestivum and Triticum durum), and rye (Secale cereale) synthesize and accumulate significant amounts of phytase during grain development as well as during germination. Other cereals, like maize (Zea mays) and rice (Oryza sativa), depend fully on de novo synthesis during germination. Despite of their importance for basic plant processes and their significance for human and livestock nutrition, little is known about the molecular composition and the mechanisms regulating phytase formation during grain development and germination. In order to unravel this, the full complement of cereals phytases is being characterized.
Proteases: Plant proteases are of fundamental biological importance but may also have a large potential as industrial enzyme in a market where ~60% of all commercialized enzymes in the world are proteases. Their fields of application are very diverse, including improving the tenderness of meat, proteases in detergents, production of fish protein hydrolysates, in antibody preparation and in brewing. Cereal cysteine proteases account for more than 90 % of the total proteolytic activity in the degradation of cereal seed storage proteins during germination. However, the complement of cysteine proteases is comprehensive and detailed characterization of the individual components is pursued for realizing the full potential.