Researchers Reveal Impact of Brassinosteroid and Sugar Signal on Wheat Grain Size Regulation

The size of grains plays a pivotal role in determining wheat yield, and the precise regulation of grain development has proven to be a key strategy in enhancing crop yields for various staples like rice and maize. However, the genetic foundation and potential molecular regulatory mechanisms governing crucial aspects of wheat grain development have remained elusive, creating a bottleneck in the quest to boost wheat yield.

 

In a recent collaborative study by Professor XIAO Jun from the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Professor BAI Mingyi at Shandong University, researchers successfully identified a gene module that regulates grain length in wheat. This research, detailed in the Plant Biotechnology Journal (https://doi.org/10.1111/pbi.14319), provides novel insights into how the interaction between brassinosteroid (BR) and sugar signals influences grain size.

 

The researchers employed a combination of genome-wide association studies and linkage analysis to pinpoint an atypical helix-loop-helix transcription factor, TabHLH489-D1, significantly correlated with grain length in wheat. TabHLH489-D1 and its homologous genes were found to decrease both grain length and thousand-grain weight. The study revealed that TaSnRK1α1 facilitates the degradation of TabHLH489 through phosphorylation, thereby promoting the elongation of seed coat cells during the early stages of wheat grain development. Sugar, in turn, induces the accumulation of TaSnRK1α1 protein, further enhancing the degradation of TabHLH489, collectively regulating wheat grain development.

 

Additionally, TabHLH489 emerged as a negative regulator of the plant hormone brassinosteroid (BR), and knocking out TabHLH489 increased sensitivity to BR in wheat. In wheat mutants featuring the BR receptor Tabzr1 and an overexpression of the BR-negative regulator kinase TaSK2, heightened TabHLH489 expression is associated with shorter wheat grains and a decrease in thousand-grain weight. Conversely, in TaSK2 knockout mutants and plants with overexpressed TaBZR1, a reduction in TabHLH489 expression leads to longer wheat grains and an increase in thousand-grain weight. Notably, TaBZR1 directly interacts with the TabHLH489 promoter, exerting a suppressive effect on its expression. Natural variations in the TabHLH489-D1 promoter region affected TaBZR1 binding, reducing the expression of TabHLH489-D1 and consequently increasing grain length.

 

This study successfully cloned the key gene TabHLH489, shedding light on its role in regulating wheat grain length. The identification of a gene functional module regulating wheat seed size and the elucidation of the regulatory mechanisms of BR and sugar on TabHLH489 at both transcriptional and protein levels mark a significant milestone. The findings not only offer crucial theoretical support but also provide valuable allelic gene resources for future wheat breeding endeavors.

 

 

Contact:

Dr. XIAO Jun

Institute of Genetics and Developmental Biology, Chinese Academy of Sciences

Email: jxiao@genetics.ac.cn