Advancing Sustainable Malting Practices: Aquaporins as Potential Breeding Targets for Improved Water Uptake during Controlled Germination of Barley (Hordeum vulgare L.)

The conversion of raw barley (Hordeum
vulgare L.) to malt requires a process of controlled
germination, where
the grain is submerged in water to raise the moisture content to >40%.
The transmembrane proteins, aquaporins, influence water uptake during
the initial stage of controlled germination, yet little is known of
their involvement in malting. With the current focus on sustainability,
understanding the mechanisms of water uptake and usage during the
initial stages of malting has become vital in improving efficient
malting practices. In this study, we used quantitative proteomics
analysis of two malting barley genotypes demonstrating differing water-uptake
phenotypes in the initial stages of malting. Our study quantified
19 transmembrane proteins from nine families, including seven distinct
aquaporin isoforms, including the plasma intrinsic proteins (PIPs)
PIP1;1, PIP2;1, and PIP2;4 and the tonoplast intrinsic proteins (TIPs)
TIP1;1, TIP2;3, TIP3;1, and TIP3;2. Our findings suggest that the
presence of TIP1;1, TIP3;1, and TIP3;2 in the mature barley grain
proteome is essential for facilitating water uptake, influencing cell
turgor and the formation of large central lytic vacuoles aiding storage
reserve hydrolysis and endosperm modification efficiency. This study
proposes that TIP3s mediate water uptake in malting barley grain,
offering potential breeding targets for improving sustainable malting
practices.