The Role of Chloroplast Membrane Lipid Metabolism in Plant Environmental Responses

Plants are nonmotile life forms that are constantly exposed to changing environmental conditions during the course of their life cycle. Fluctuations in environmental conditions can be drastic during both day–night and seasonal cycles, as well as in the long term as the climate changes. Plants are naturally adapted to face these environmental challenges, and it has become increasingly apparent that membranes and their lipid composition are an important component of this adaptive response. Plants can remodel their membranes to change the abundance of different lipid classes, and they can release fatty acids that give rise to signaling compounds in response to environmental cues. Chloroplasts harbor the photosynthetic apparatus of plants embedded into one of the most extensive membrane systems found in nature. In part one of this review, we focus on changes in chloroplast membrane lipid class composition in response to environmental changes, and in part two, we will detail chloroplast lipid-derived signals.

The rice BZ1 locus is required for glycosylation of arabinogalactan proteins and galactolipid and plays a role in both mechanical strength and leaf color

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.

The rice BZ1 locus is required for glycosylation of arabinogalactan proteins and galactolipid and plays a role in both mechanical strength and leaf color

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 upmost 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 (MDGD), 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 sidechain biosynthesis of AGPs and MDGD, 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 MDGD and suggests a strategy for breeding robust elite crops.