Oryzalexin S biosynthesis: a cross-stitched disappearing pathway
Le Zhao1, Richard Oyagbenro1, Yiling Feng1
1Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011 USA.
Abiotech
|May 23, 2023
Summary
Rice phytoalexin biosynthesis involves two gene clusters, with oryzalexin S production dependent on genes from both. Subspecies-specific gene presence explains variations in oryzalexin S production between rice varieties.
Area of Science:
- Plant biochemistry and molecular biology
- Genomics and metabolomics of crop plants
- Natural product biosynthesis in cereals
Background:
- Rice produces diterpenoid phytoalexins crucial for its defense mechanisms.
- Biosynthetic gene clusters (BGCs) in rice encode enzymes for these natural products.
- The chromosome 4 BGC (c4BGC) is linked to momilactone production via OsCPS4.
Purpose of the Study:
- To elucidate the complete biosynthetic pathway of the rice phytoalexin oryzalexin S.
- To identify the specific cytochrome P450 (CYP) monooxygenases involved in oryzalexin S production.
- To investigate the genetic basis for subspecies-specific differences in oryzalexin S biosynthesis.
Main Methods:
- Analysis of gene locations within rice BGCs.
- Enzymatic characterization of CYP99A2, CYP99A3, CYP71Z21, and CYP71Z22.
- Comparative genomics of BGCs across rice subspecies (ssp. japonica and ssp. indica).
Main Results:
- Oryzalexin S biosynthesis requires enzymes encoded by two distinct BGCs: c4BGC and the chromosome 7 BGC (c7BGC).
- CYP99A2/A3 catalyze C19-hydroxylation, while CYP71Z21/Z22 catalyze C2α-hydroxylation, both essential steps for oryzalexin S.
- The c7BGC is prevalent in ssp. japonica but rare in ssp. indica, correlating with oryzalexin S production differences.
Conclusions:
- Oryzalexin S biosynthesis is a complex, cross-stitched pathway involving multiple BGCs.
- Subspecies-specific distribution of the c7BGC underlies variations in oryzalexin S production.
- Evidence suggests introgression of ssp. indica alleles (OsKSL11) into japonica, leading to loss of oryzalexin S production in some japonica varieties.
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