The Rice BZ1 Locus Is Required for Glycosylation of Arabinogalactan Proteins and Galactolipid and Plays a Role in both Mechanical Strength and Leaf Color

• Published in: Rice (New York, N.Y.) Vol. 13; no. 1; p. 41
• Main Authors: Liu, Sitong, Tang, Yijun, Ruan, Nan, Dang, Zhengjun, Huang, Yuwei, Miao, Wei, Xu, Zhengjin, Li, Fengcheng
• Format: Journal Article
• Language: English
• Published: New York Springer US 17-06-2020; Springer Nature B.V; SpringerOpen
• Subjects: AGPs; Agriculture; Agronomy; Arabinogalactan; Biochemical analysis; Biomedical and Life Sciences; Biosynthesis; Cell wall; Cell walls; Cellulose; Chloroplasts; Crop yield; Epimerase; Galactose; Gene expression; Glycosylation; Leaf color; Leaves; Life Sciences; Lipids; Mechanical properties; Mechanical strength; Membranes; Metabolism; MGDG; Original; Original Article; Photosynthesis; Plant breeding; Plant Breeding/Biotechnology; Plant Ecology; Plant Genetics and Genomics; Plant growth; Plant Sciences; Plant tissues; Proteins; Rice; Robustness; Scanning electron microscopy; Stems; Tissue analysis; UDP-galactose/glucose epimerase; Mechanical strength; AGPs; MGDG; Leaf color; Cell wall; Chloroplast; UDP-galactose/glucose epimerase
• ISSN: 1939-8425; 1939-8433; 1934-8037
• DOI: 10.1186/s12284-020-00400-9

Background
The cell wall and chloroplast are two fundamental structures determining plant mechanical strength and grain yield. Therefore, understanding mechanisms that improve plants’ ability to develop a robust cell wall and well-developed chloroplast is of utmost importance for agricultural activities.
Results
In this study, we report the functional characterization of a novel rice mutant, brittle stem and zebra leaf (
bz1
), which displays altered cell wall composition and collapsed chloroplast membrane. Molecular and biochemical analysis revealed that BZ1 encodes a functional UDP-galactose/glucose epimerase (UGE) and is ubiquitously expressed with higher expression in stem and leaf tissues. Multiple techniques analyses, including immunoblots, immuno-gold, and cryogenic scanning electron microscopy, demonstrated a significantly impaired glycosylation of arabinogalactan proteins (AGPs) and disordered cellulose microfibril deposition in
bz1
. Lipid profiling assay showed that the amount of monogalactosyldiacylglycerols (MGDG), a major chloroplast membrane glycolipid, was significantly decreased in
bz1
. Taken together, these results strongly demonstrate that BZ1 participates in UDP-galactose supply for the sugar chains biosynthesis of AGPs and MGDG, which thereby, respectively, results in altered cell wall and abnormal chloroplast development. Due to inferior mechanical strength and reduced photosynthesis,
bz1
plants displayed detrimental agronomic traits, whereas BZ1 overexpressing lines showed enhanced plant growth. Transcriptome analysis of stems and leaves further showed that numerous key genes involved in AGPs biosynthesis and photosynthesis metabolism were substantially suppressed in
bz1
.
Conclusions
Our finding identifies BZ1 as a dual-targeting UGE protein for glycosylation of AGPs and MGDG and suggests a strategy for breeding robust elite crops.