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Rice contains a biosynthetic gene cluster associated with production of the casbane-type diterpenoid phytoalexin ent-10-oxodepressin.

ABSTRACT: Diterpenoids play important roles in rice microbial disease resistance as phytoalexins, as well as acting in allelopathy and abiotic stress responses. Recently, the casbane-type phytoalexin ent-10-oxodepressin was identified in rice, but its biosynthesis has not yet been elucidated. Here ent-10-oxodepressin biosynthesis was investigated via co-expression analysis and biochemical characterisation, with use of the CRISPR/Cas9 technology for genetic analysis. The results identified a biosynthetic gene cluster (BGC) on rice chromosome 7 (c7BGC), containing the relevant ent-casbene synthase (OsECBS), and four cytochrome P450 (CYP) genes from the CYP71Z subfamily. Three of these CYPs were shown to act on ent-casbene, with CYP71Z2 able to produce a keto group at carbon-5 (C5), while the closely related paralogues CYP71Z21 and CYP71Z22 both readily produce a keto group at C10. Together these C5 and C10 oxidases can elaborate ent-casbene to ent-10-oxodepressin (5,10-diketo-ent-casbene). OsECBS knockout lines no longer produce casbane-type diterpenoids and exhibit impaired resistance to the rice fungal blast pathogen Magnaporthe oryzae. Elucidation of ent-10-oxodepressin biosynthesis and the associated c7BGC provides not only a potential target for molecular breeding, but also, gives the intriguing parallels to the independently assembled BGCs for casbene-derived diterpenoids in the Euphorbiaceae, further insight into plant BGC evolution, as discussed here.

SUBMITTER: Liang J

PROVIDER: S-EPMC9044444 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background and Aims:MicroRNAs (miRNAs) are small non-coding RNAs that act as post-transcriptional regulators of gene expression via sequence-specific cleavage or translational repression of target transcripts. They are transcribed as long single-stranded RNA precursors with unique stem-loop structures that are processed by a DICER-Like (DCL) ribonuclease, typically DCL1, to produce mature miRNAs. Although a plethora of miRNAs have been found to be regulated by pathogen infection in plants, the biological function of most miRNAs remains largely unknown. Here, the contribution of OsDCL1 to rice immunity was investigated. Methods:Activation-tagged Osdcl1a (Osdcl1a-Ac) rice mutants were examined for resistance to pathogen infection. mRNA and small RNA deep sequencing, quantitative real-time PCR (RT-qPCR) and stem-loop reverse tanscripion-PCR (RT-PCR) were used to examine DCL1a-mediated alterations in the rice transcriptome. Rice diterpene phytoalexins were quantified by liquid chromatography-tandem mass spectrometry (LC-MSMS). Accumulation of O2·- was determined by nitroblue tetrazolium (NBT) staining. Key Results:dcl1a-Ac mutants exhibit enhanced susceptibility to infection by fungal pathogens which was associated with a weaker induction of defence gene expression. Comparison of the mRNA and miRNA transcriptomes of dcl1a-Ac and wild-type plants revealed misregulation of genes involved in detoxification of reactive oxygen species. Consequently, dcl1a-Ac plants accumulated O2·- in their leaves and were more sensitive to methyl viologen-induced oxidative stress. Furthermore, dcl1a-Ac plants showed downregulation of diterpenoid phytoalexin biosynthetic genes, these genes also being weakly induced during pathogen infection. Upon pathogen challenge, dcl1a-Ac plants failed to accumulate major diterpenoid phytoalexins. OsDCL1a activation resulted in marked alterations in the rice miRNAome, including both upregulation and downregulation of miRNAs. Conclusions:OsDCL1a activation enhances susceptibility to infection by fungal pathogens in rice. Activation of OsDCL1a represses the pathogen-inducible host defence response and negatively regulates diterpenoid phytoalexin production. These findings provide a basis to understand the molecular mechanisms through which OsDCL1a mediates rice immunity.

Dataset Information

Rice contains a biosynthetic gene cluster associated with production of the casbane-type diterpenoid phytoalexin ent-10-oxodepressin.

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