Date Published: May 23, 2019
Publisher: Public Library of Science
Author(s): Keiko Midorikawa, Masaharu Kuroda, Haruyuki Yamashita, Tomoko Tamura, Keiko Abe, Tomiko Asakura, Sara Amancio.
The endosperm cell wall affects post-harvest grain quality by affecting the mechanical fragility and water absorption of the grain. Therefore, understanding the mechanism underlying endosperm cell wall synthesis is important for determining the growth and quality of cereals. However, the molecular machinery mediating endosperm cell wall biosynthesis is not well understood. In this study, we investigated the role of Oryza sativa Brittle Culm 1-like 6 (OsBC1L6), a member of the COBRA-like protein family, in cellulose synthesis in rice. OsBC1L6 mRNA was expressed in ripening seeds during endosperm enlargement. When OsBC1L6-RFP was expressed in Arabidopsis cell cultures, this fusion protein was transported to the plasma membrane. To investigate the target molecules of OsBC1L6, we analyzed the binding interactions of OsBC1L6 with cellohexaose and the analogs using surface plasmon resonance, determining that cellohexaose bound to OsBC1L6. The β-glucan contents were significantly reduced in OsBC1L6-RNAi calli and OsBC1L6-deficient seeds from a Tos insertion mutant, compared to their wild-type counterparts. These findings suggest that OsBC1L6 modulates β-glucan synthesis during endosperm cell wall formation by interacting with cellulose moieties on the plasma membrane during seed ripening.
The endosperm cell wall functions in a variety of processes in cereals, including morphogenesis and ripening, cell and tissue protection, polysaccharide storage, and the selective permeation of enzymes and hydrolysates during germination [1–3]. From a food processing standpoint, the cell wall is important because it determines the fragility, quality, and water-absorbing properties of grains [4–6].
We previously reported that nitrogen fertilization at the heading stage reduces the expression of various genes for endosperm cell wall production . In particular, reduced levels of β-glucan in the endosperm of fertilized seeds appear to be correlated with the reduced expression of genes involved in cellulose biosynthesis. Cellulose, a polysaccharide composed of (1, 4)-β-D-glucans, is a major component of the endosperm cell wall presumed to be involved in the mechanical strength and water permeability of polished rice [4–6]. Our results present a possibility that functional analysis of each fertilizer-responsive, cellulose-related gene discloses a relationship between cellulose and rice quality.