Enzyme Key to Preventing Early Sprouting in Rice

Jim Crocker
19th April, 2024

Enzyme Key to Preventing Early Sprouting in Rice

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Nanjing Agricultural University discovered a gene, OsAAH, that affects rice seed sprouting before harvest
  • When OsAAH is disrupted, rice seeds have higher energy levels, which may lead to premature sprouting
  • The study suggests that manipulating OsAAH could help breed rice varieties resistant to preharvest sprouting, reducing crop losses
Rice is a staple food for more than half of the world's population, and its production is crucial for global food security. One challenge in rice cultivation is preharvest sprouting (PHS), a condition where seeds germinate on the plant before harvest, leading to significant losses in yield and quality. To combat this issue, researchers at Nanjing Agricultural University have made a breakthrough in understanding the genetic factors behind PHS in rice[1]. The team identified a mutant strain of rice, named preharvest sprouting 39 (phs39), which showed a clear tendency to sprout prematurely in the field. Using a method called MutMap+[2], which compares genetic differences between mutant and non-mutant plants, the researchers pinpointed the gene responsible for this trait: OsAAH, which stands for allantoate amidohydrolase. OsAAH is an enzyme that plays a role in breaking down a substance called allantoate. This process is part of a larger metabolic pathway that affects the plant's energy levels and hormonal balance. The study found that when the OsAAH gene is disrupted, the levels of allantoate and another compound called allantoin increase. This change appears to activate the tricarboxylic acid (TCA) cycle, an essential pathway for energy production in cells, leading to higher energy levels in the developing seeds. Increased energy in the seed is thought to encourage germination, which is precisely what farmers don't want to happen before the rice is harvested. Additionally, the disruption of OsAAH affects the balance of certain amino acids and plant hormones. Specifically, the researchers noted altered levels of asparagine, arginine, lysine, and tryptophan. They also observed reduced levels of two key plant hormones: indole-3-acetic acid (IAA) and abscisic acid (ABA). ABA is known to play a critical role in maintaining seed dormancy and preventing PHS[3][4][5]. The findings from Nanjing Agricultural University's study align with previous research that has highlighted the importance of ABA and hormonal balance in preventing PHS. For example, the OsNCED3 gene has been shown to regulate ABA levels, affecting seed dormancy and PHS resistance in rice[3]. Similarly, sugars in the endosperm have been found to influence ABA signaling and seed germination[4], while mutations in carotenoid biosynthesis genes, which are precursors to ABA, have been linked to reduced ABA levels and increased PHS[5]. The study's revelation that OsAAH is involved in PHS through its role in energy and hormone metabolism opens up new avenues for breeding PHS-resistant rice varieties. By understanding the genetic and molecular mechanisms behind PHS, scientists and breeders can develop targeted strategies to mitigate this problem. For instance, by manipulating the OsAAH gene or the pathways it influences, it may be possible to produce rice plants that are less likely to sprout before harvest. This research not only contributes to the body of knowledge on PHS but also offers practical solutions to a problem that affects rice farmers worldwide. By reducing the incidence of PHS, rice yields can be preserved, and the quality of the harvested grain can be maintained, ensuring that this vital crop continues to sustain the growing global population.

BiochemPlant ScienceAgriculture

References

Main Study

1) Allantoate Amidohydrolase OsAAH is Essential for Preharvest Sprouting Resistance in Rice

Published 16th April, 2024

https://doi.org/10.1186/s12284-024-00706-y

Related Studies

2) MutMap+: genetic mapping and mutant identification without crossing in rice.

https://doi.org/10.1371/journal.pone.0068529

3) ABA biosynthesis gene OsNCED3 contributes to preharvest sprouting resistance and grain development in rice.

https://doi.org/10.1111/pce.14480

4) Endosperm sugar accumulation caused by mutation of PHS8/ISA1 leads to pre-harvest sprouting in rice.

https://doi.org/10.1111/tpj.13970

5) Mutations of genes in synthesis of the carotenoid precursors of ABA lead to pre-harvest sprouting and photo-oxidation in rice.

https://doi.org/10.1111/j.1365-313X.2008.03411.x


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