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A QTL for rice grain width and weight encodes a previously unknown RING-type E3 ubiquitin ligase

Abstract

Grain weight is one of the most important components of grain yield and is controlled by quantitative trait loci (QTLs) derived from natural variations in crops. However, the molecular roles of QTLs in the regulation of grain weight have not been fully elucidated. Here, we report the cloning and characterization of GW2, a new QTL that controls rice grain width and weight. Our data show that GW2 encodes a previously unknown RING-type protein with E3 ubiquitin ligase activity, which is known to function in the degradation by the ubiquitin-proteasome pathway. Loss of GW2 function increased cell numbers, resulting in a larger (wider) spikelet hull, and it accelerated the grain milk filling rate, resulting in enhanced grain width, weight and yield. Our results suggest that GW2 negatively regulates cell division by targeting its substrate(s) to proteasomes for regulated proteolysis. The functional characterization of GW2 provides insight into the mechanism of seed development and is a potential tool for improving grain yield in crops.

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Figure 1: Map-based cloning of GW2.
Figure 2: Structure and molecular characterization of GW2.
Figure 3: Cellular properties and expression pattern of GW2.
Figure 4: Phenotypic characterization of grains in FAZ1 and NIL(GW2).
Figure 5: Histological analyses of spikelet hulls just before heading and endosperm at maturity in FAZ1 and NIL(GW2).
Figure 6: Characterization of grain milk filling in FAZ1 and NIL(GW2) and proposed model for the role of GW2.

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Acknowledgements

We thank P. Qi and Z.-Z. Piao for technical assistance. We thank S. Luan for critically reading the manuscript. This work was supported by grants from the Ministry of Science and Technology of China and the Shanghai Science and Technology Development Fund to H.-X.L.

Author information

Authors and Affiliations

Authors

Contributions

H.-X.L. designed the experiments. X.J.S. and W.H. performed most of the experiments. H.-X.L., S.M. and M.Z.Z. performed some of the experiments. H.-X.L. wrote the manuscript.

Corresponding author

Correspondence to Hong-Xuan Lin.

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Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Grain phenotypes of FAZ1, WY3 and Oochikara. (PDF 29 kb)

Supplementary Fig. 2

GW2 expression in transgenic lines. (PDF 29 kb)

Supplementary Fig. 3

Comparison of plant height, flag leaf width, panicle number per plant, days to heading and main panicle length in FAZ1 and NIL(GW2). (PDF 34 kb)

Supplementary Fig. 4

Phenotypic characterization of grains in reciprocal crosses between FAZ1 and NIL(GW2). (PDF 31 kb)

Supplementary Fig. 5

Endosperm at various time points after fertilization. (PDF 52 kb)

Supplementary Fig. 6

Comparison of the six rice grain quality traits in FAZ1 and NIL1(GW2). (PDF 56 kb)

Supplementary Table 1

Molecular marker primers and primers for GW2 molecular analysis. (PDF 11 kb)

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Song, XJ., Huang, W., Shi, M. et al. A QTL for rice grain width and weight encodes a previously unknown RING-type E3 ubiquitin ligase. Nat Genet 39, 623–630 (2007). https://doi.org/10.1038/ng2014

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