Strategic Distribution of Protective Proteins within Bran Layers of Wheat Protects the Nutrient-Rich Endosperm

Abstract

Bran from bread wheat (Triticum aestivum ‘Babbler’) grain is composed of many outer layers of dead maternal tissues that overlie living aleurone cells. The dead cell layers function as a barrier resistant to degradation, whereas the aleurone layer is involved in mobilizing organic substrates in the endosperm during germination. We microdissected three defined bran fractions, outer layers (epidermis and hypodermis), intermediate fraction (cross cells, tube cells, testa, and nucellar tissue), and inner layer (aleurone cells), and used proteomics to identify their individual protein complements. All proteins of the outer layers were enzymes, whose function is to provide direct protection against pathogens or improve tissue strength. The more complex proteome of the intermediate layers suggests a greater diversity of function, including the inhibition of enzymes secreted by pathogens. The inner layer contains proteins involved in metabolism, as would be expected from live aleurone cells, but this layer also includes defense enzymes and inhibitors as well as 7S globulin (specific to this layer). Using immunofluorescence microscopy, oxalate oxidase was localized predominantly to the outer layers, xylanase inhibitor protein I to the xylan-rich nucellar layer of the intermediate fraction and pathogenesis-related protein 4 mainly to the aleurone. Activities of the water-extractable enzymes oxalate oxidase, peroxidase, and polyphenol oxidase were highest in the outer layers, whereas chitinase activity was found only in assays of whole grains. We conclude that the differential protein complements of each bran layer in wheat provide distinct lines of defense in protecting the embryo and nutrient-rich endosperm.

NKD Transcription Factors Are Central Regulators of Maize Endosperm Development

“…NKD1 and NKD2 directly activate vp1 transcription and are predicted to directly 469 activate r1 ( Figure 7B; Supplemental Datasets 1, 2 and 3). endosperm and the only cell type alive at maturity; thus, it is fundamentally important for 478 defense to pathogens (Jerkovic et al, 2010). Among predicted direct targets was 479 xylanase inhibitor protein-1 (XIP-1), which is involved in fungal defense (Moscetti et al, 480 2013) Several key TFs were shown or predicted to be direct targets of NKD regulation, 492 including O2, PBF1, VP1 and R1.…”

“…BET cells transport nutrients from maternal tissue into the 44 developing endosperm. AL is important for digestion and remobilization of stored 45 reserves during germination as well as mineral storage and pathogen defense (Stewart 46 et al, 1988;Fath et al, 2000;Jerkovic et al, 2010). 47 4 To identify genes and biological processes directly or indirectly regulated by NKD1 and 91 NKD2 (NKD1/2) in developing endosperm, a transcriptomic analysis was undertaken to 92 identify gene transcripts differentially expressed (DE) between WT and nkd1 nkd2 93 mutant.…”

Current potential and limitations of immunolabeling in cereal grain research

“…However, the outer layers (bran without aleurone), transfer cells, and the embryo (germ) remain less well characterized (Beaugrand, et al, 2005;Chen, et al, 2012;Jerkovic, et al, 2010;Robert, et al, 2011). Table 1.…”

“…Outer layers / Bran without aleurone Arabinoxylan Wheat (Beaugrand et al, 2005;Beaugrand, Reis, et al, 2004;Philippe et al, 2006;Philippe et al, 2007); oat, rye, barley (13),(14)--D-glucan Wheat (Philippe et al, 2006) Callose Wheat (Philippe et al, 2006) Ferulic acid Wheat (Philippe et al, 2007) Xylanase Wheat (Beaugrand, Cronier, et al, 2004;Beaugrand et al, 2005;Beaugrand, Reis, et al, 2004) Oxalate oxidase Wheat (Jerkovic et al, 2010) Xylanase inhibitor I protein Wheat (Jerkovic et al, 2010) Wheatwin1 Wheat (Jerkovic et al, 2010) …”

“…A better understanding of the outer layers of cereal grain has been obtained in the past few years (Beaugrand, Cronier, et al, 2004;Beaugrand, et al, 2005;Beaugrand, Reis, et al, 2004;Jerkovic, et al, 2010;Philippe, et al, 2007). For example, Beaugrand, Cronier, et al (2004) evaluated the impact of outer-layer changes across grain ripening on in situ degradation of AX in the peripheral grain tissues by immunolocalization of a (14)--endoxylanase.…”