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.

中文翻译：

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水稻BZ1位点是阿拉伯半乳聚糖蛋白和半乳糖脂糖基化的必需条件，并且在机械强度和叶片颜色中均起作用。

背景

细胞壁和叶绿体是决定植物机械强度和谷物产量的两个基本结构。因此，了解提高植物形成健壮的细胞壁和成熟的叶绿体能力的机制对于农业活动至关重要。

结果

在这项研究中，我们报告了新型水稻突变体，脆性茎和斑马叶（bz1）的功能特征，该突变体显示出改变的细胞壁组成和塌陷的叶绿体膜。分子和生化分析表明，BZ1编码功能性UDP-半乳糖/葡萄糖差向异构酶（UGE），并在茎和叶组织中普遍表达，并具有较高的表达水平。多种技术分析，包括免疫印迹，免疫金和低温扫描电子显微镜，均证明阿拉伯半乳聚糖蛋白（AGP）的糖基化显着受损以及bz1中无序的纤维素微纤维沉积。脂质谱测定法表明，monogalactosyldiacylglycerols的量（MGDG），一个主要的叶绿体膜糖脂，被显著下降BZ1。综上所述，这些结果有力地证明了BZ1参与UDP-半乳糖供应，用于AGP和MGDG的糖链生物合成，从而分别导致细胞壁改变和叶绿体发育异常。由于机械强度较低和光合作用降低，bz1植物表现出有害的农艺性状，而BZ1过表达品系显示植物的生长增强。茎和叶的转录组分析进一步表明，bz1中大量抑制了AGPs生物合成和光合作用代谢的关键基因。

结论

我们的发现将BZ1识别为AGP和MGDG糖基化的双重目标UGE蛋白，并提出了育种强壮精英作物的策略。