Source ability is regulated by THOUSAND-GRAIN WEIGHT 6 in rice

Area of Science:

• Plant Biology
• Crop Science
• Molecular Genetics

Background:

• THOUSAND-GRAIN WEIGHT 6 (TGW6) is an indole-3-acetic acid (IAA)-glucose hydrolase that negatively regulates rice grain weight and starch accumulation.
• A loss-of-function mutation in TGW6 enhances grain size and yield, making it a key target for rice breeding.
• The impact of TGW6 loss-of-function on source ability (carbohydrate production and supply) in rice remains largely uncharacterized.

Purpose of the Study:

• To investigate the effect of TGW6 loss-of-function on source ability, specifically shoot carbohydrate accumulation and translocation in rice.
• To analyze starch content, gene expression related to starch metabolism, and carbohydrate translocation in rice leaves.

Main Methods:

• Comparison of starch content in lower leaf sheaths between a wild-type rice cultivar (cv. Koshihikari) and a near-isogenic line with TGW6 loss-of-function (NIL(TGW6)).
• Gene expression analysis of starch synthesis and degradation pathways in lower leaf sheaths.
• Measurement of carbohydrate accumulation to assess translocation efficiency.

Main Results:

• The NIL(TGW6) line exhibited significantly higher starch accumulation in lower leaf sheaths compared to cv. Koshihikari.
• Gene expression analysis revealed up-regulation of starch synthesis genes and down-regulation of starch degradation genes in NIL(TGW6).
• Loss of TGW6 function was found to activate carbohydrate translocation, with leaf sheath starch contributing to increased starch upload into panicles.

Conclusions:

• Loss of TGW6 function enhances rice source ability by promoting starch accumulation in leaf sheaths and activating carbohydrate translocation.
• This mechanism directly contributes to increased starch supply to developing grains, ultimately enhancing rice yield.
• These findings offer novel insights into TGW6's role in regulating source-sink relationships and improving crop productivity.