Disruption of ζ-Carotene Desaturase Protein ALE1 Leads to Chloroplast Developmental Defects and Seedling Lethality.

ζ-carotene desaturase (ZDS) is a key enzyme in carotenoid biosynthesis and plays an important role in plant photosynthesis. We characterized an albino leaf-color mutant obtained from ethyl methanesulfonate treatment: albino and seedling lethality 1 (ale1). The material contains a chloroplast thylakoid defect where photosynthetic pigments declined and reactive oxygen species accumulated resulting in ale1 death within 3 weeks. Positional cloning and sequencing revealed that there was a single base substitution in ALE1, which encoded a ZDS involved in carotenoid biosynthesis. RNAi and complementation tests confirmed the identity of ALE1. Subcellular localization showed that the ALE1 protein is localized in the chloroplast. Expression analysis indicated that the genes involved in chlorophyll and carotenoid biosynthesis were downregulated. We conclude that ALE1 plays an important role in chloroplast and plant growth in rice.

Single-point Mutation of an Histidine-aspartic Domain-containing Gene involving in Chloroplast Ribosome Biogenesis Leads to White Fine Stripe Leaf in Rice.

Plant leaves are a crucial organ associated closely with chloroplast development, photosynthesis rate and crop productivity. In this study, a white fine stripe leaf 1 (wfsl1) mutant was isolated and characterized from the japonica rice Zhonghua11 (ZH11) after ethyl methanesulfonate mutagenesis. The wfsl1 displayed white fine stripe leaves since tillering stage and abnormal chloroplast structure. Map-based cloning and Bioinformatic analysis indicated that WFSL1 on chromosome 1 contains an "A" to "T" substitution in protein coding region, and encodes a putative metal-dependent phosphohydrolase with HD domain at the N-terminus. WFSL1 was targeted to the chloroplasts and had higher expression in mature leaves and sheaths. RNA-seq analysis revealed that chloroplast development and photosynthesis genes were significantly affected in wfsl1 plants. Levels of WFSL1 and chloroplast encoded proteins were decreased in wfsl1 mutants via western blot analysis. Compared with WT, wfsl1 exhibits lower Chl content and defective in biogenesis of chloroplast ribosomes, which resulted in reduced grain yield. Taken together, our results show that WFSL1 is critical for chloroplast development, ribosome biogenesis, and light energy utilization, finally affects grain yield.

A Rare Allele of GS2 Enhances Grain Size and Grain Yield in Rice.

Grain size determines grain weight and affects grain quality. Several major quantitative trait loci (QTLs) regulating grain size have been cloned; however, our understanding of the underlying mechanism that regulates the size of rice grains remains fragmentary. Here, we report the cloning and characterization of a dominant QTL, grain size on chromosome 2 (GS2), which encodes Growth-Regulating Factor 4 (OsGRF4), a transcriptional regulator. GS2 localizes to the nucleus and may act as a transcription activator. A rare mutation of GS2 affecting the binding site of a microRNA, OsmiR396c, causes elevated expression of GS2/OsGRF4. The increase in GS2 expression leads to larger cells and increased numbers of cells, which thus enhances grain weight and yield. The introduction of this rare allele of GS2/OsGRF4 into rice cultivars could significantly enhance grain weight and increase grain yield, with possible applications in breeding high-yield rice varieties.

Measuring the damage of heavy metal cadmium in rice seedlings by SRAP analysis combined with physiological and biochemical parameters.

BACKGROUND: Cadmium (Cd) is one of the most poisonous pollutants, and Cd pollution has become the limiting factor of rice production and quality improvement. Therefore it is of significant importance to monitor Cd toxicity by the detection of Cd contamination in rice with biomarkers. In the present study, sequence-related amplified polymorphism (SRAP) and physiological and biochemical methods were applied to determine the toxicological effects of Cd stress on rice. RESULTS: With increasing Cd concentration and duration, the content of chlorophyll in the two rice varieties W7 and M63 decreased and that of malondialdehyde increased. This tendency was more apparent in M63. The antioxidant enzymes superoxide dismutase and peroxidase both increased significantly compared with controls. SRAP polymerase chain reaction results indicated significant differences between Cd treatments and controls in terms of SRAP profile, as well as genotypic differences. The genomic template stability (GTS) decreased with increasing Cd concentration and duration. Under the same treatment conditions, the GTS of W7 was higher than that of M63. Comparison analysis revealed that the changes in physiological and biochemical parameters of rice seedlings under Cd stress had a good correlation with the changes in SRAP profile. Furthermore, the changes in SRAP profile showed enhanced sensitivity in the roots of rice seedlings. CONCLUSION: The SRAP profile and physiological and biochemical parameters could act as appropriate biomarkers for the measurement of Cd contamination during rice production.