Plasma membrane‐localized SEM1 protein mediates sugar movement to sink rice tissues

Abstract

The translocation of photosynthate carbohydrates, such as sucrose, is critical for plant growth and crop yield. Previous studies have revealed that sugar transporters, plasmodesmata and sieve plates act as important controllers in sucrose loading into and unloading from phloem in the vascular system. However, other pivotal steps for the regulation of sucrose movement remain largely elusive. In this study, characterization of two starch excesses in mesophyll (sem) mutants and dye and sucrose export assays were performed to provide insights into the regulatory networks that drive source-sink relations in rice. Map-based cloning identified two allelic mutations in a gene encoding a GLUCAN SYNTHASE-LIKE (GSL) protein, thus indicating a role for SEM1 in callose biosynthesis. Subcellular localization in rice showed that SEM1 localized to the plasma membrane. In situ expression analysis and GUS staining showed that SEM1 was mainly expressed in vascular phloem cells. Reduced sucrose transport was found in the sem1-1/1-2 mutant, which led to excessive starch accumulation in source leaves and inhibited photosynthesis. Paraffin section and transmission electron microscopy experiments revealed that less-developed vascular cells (VCs) in sem1-1/1-2 potentially disturbed sugar movement. Moreover, dye and sugar trafficking experiments revealed that aberrant VC development was the main reason for the pleiotropic phenotype of sem1-1/1-2. In total, efficient sucrose loading into the phloem benefits from an optional number of VCs with a large vacuole that could act as a buffer holding tank for sucrose passing from the vascular bundle sheath.

Disruption of BG14 results in enhanced callose deposition in developing seeds and decreases seed longevity and seed dormancy in Arabidopsis

“…Callose extraction and quantification were performed as described previously (Wang et al., 2022). Seeds (0.1 g) were fixed with ethanol at 4°C for 12 h, homogenized in 1 m NaOH for 2 min and incubated at 80°C for 15 min.…”

“…Seeds (0.1 g) were ground in 1 ml of 0.1 m citric acid sodium citrate buffer (pH 5.0), and the enzyme solution was extracted according to the method described by Wang et al. (2022). The degradation reaction contained 0.2 ml of enzyme solution and 0.2 ml of 1 mg ml −1 laminarin, and was incubated at 30°C for 1 h. After adding 0.6 ml of 3,5‐dinitrosalicylic acid into the reaction, the reactions were incubated in a boiling water bath for 15 min, and then the glucose content was determined by spectrophotometry at 550 nm.…”

RLM1, Encoding an R2R3 MYB Transcription Factor, Regulates the Development of Secondary Cell Wall in Rice

“…Stem samples from leaves or the 2nd internode were collected from rice at the heading stage. The tissues were cut to 0.5 cm and fixed in 2.5% glutaraldehyde for 12 h. The samples were prepared according to the methods of Wang et al (2022) and then imaged with a scanning electron microscope (H-7500, Hitachi, Japan).…”

Editorial: Environmental and endogenous signals: crop yield and quality regulation

“…Studies have shown that grain filling is affected by changes in the expression of genes related to photosynthetic capacity, such as those associated with source-sink translocation ( Brazel and Ó'Maoiléidigh, 2019 ; Sanchez-Bragado et al., 2020 ; Zhang et al., 2022 ). Additionally, nutritional transport systems such as transporters of nutrient elements ( Shannon, 1972 ; Sosso et al., 2015 ; Bezrutczyk et al., 2018 ; Wang et al., 2018 ; Shen et al., 2022 ; Wang et al., 2022 ; Yang B. et al., 2022 ; Sun et al., 2023 ), plasmodesmata, and sieve plates are essential to grain filling determination ( Zhang et al., 2010 ; You et al., 2021 ). Lastly, enzymes that synthesize storage starch ( Hannah and James, 2008 ; Huang et al., 2021 ; Wang et al., 2021 ) and lipids ( Yang Y. et al., 2022 ; Luo et al., 2023 ) and genes that encode storage proteins ( Yang et al., 2023 ; Zhao et al., 2023 ) in seeds work together to determine grain yield and quality of the cereal crops.…”