what do you know about Pentacyclic triterpene synthase 1 (Arabidopsis thaliana, At4G15340.1)?

Pentacyclic triterpene synthase 1 (also known as PEN1 or arabidiol synthase, encoded by the gene At4G15340) is a key oxidosqualene cyclase in Arabidopsis thaliana that catalyzes the formation of the triterpene diol arabidiol, which serves as a precursor for defensive volatile compounds.

Biochemical Function and Pathway

• Catalytic Activity: PEN1 is an oxidosqualene cyclase that converts the precursor 2,3-oxidosqualene into the tricyclic triterpene diol arabidiol (Direct, High; PMID: 36582057).
• DMNT Biosynthesis: Arabidiol is the direct precursor for the volatile homoterpene (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). This conversion is mediated by the cytochrome P450 monooxygenase CYP705A1 (Direct, High; PMID: 36582057).
• Metabolic Cluster: The expression of PEN1 is synergistically associated with CYP705A1, forming a specialized metabolic network (Direct, High; PMID: 36582057).

Expression and Regulation

• Tissue Specificity: PEN1 is primarily expressed in Arabidopsis roots (Direct, High; PMID: 36582057, PMID: 33599614).
• Negative Regulation by RPX1: The gene is regulated by RPX1 (a novel cap-binding protein). Inactivation or knockdown of RPX1 leads to significantly higher transcript levels of PEN1, resulting in the over-accumulation of DMNT (Direct, High; PMID: 36582057).
• Response to Biotic Stress: PEN1 expression is significantly upregulated following infestation by the diamondback moth, Plutella xylostella (Direct, High; PMID: 33599614, PMID: 36582057).

Physiological and Ecological Role

• Mechanism of Action: The DMNT produced via the PEN1 pathway acts as a bioinsecticide. It repels larvae and causes mortality by disrupting the peritrophic matrix (PM) barrier in the insect midgut, a process that requires the presence of midgut microbiota (Direct, High; PMID: 33599614).
• Systemic Defense: While PEN1 is expressed mainly in the roots, the resulting DMNT can be transported to the aerial parts of the plant to provide resistance in leaves (Direct, High; PMID: 36582057).
• Growth Trade-offs: Higher PEN1 expression and RPX1 mutation provide pest resistance without the typical trade-off in plant growth or seed production (Direct, High; PMID: 36582057).

How does the transport of DMNT from roots to leaves affect systemic pest resistance in Arabidopsis?

What specific role does the midgut microbiota play in the PEN1-mediated killing of Plutella xylostella?

What are the known regulatory mechanisms by which RPX1 influences PEN1 mRNA stability or translation?

Unverified Citations

The following sources failed to support their assigned claims after 3 verification rounds designed to ensure only high-confidence, relevant references are retained:

• PMID:31758060 — ** Catalytic Activity: PEN1 is an oxidosqualene cyclase that converts the precursor 2,3-oxidosqualene into the ...*
  Failed: mechanism,entities — The paper focuses on DMNT signaling and Sporamin induction in sweet potato and does not mention PEN1, 2,3-oxidosqualene, or arabidiol.
• PMID:33599614 — This conversion is mediated by the cytochrome P450 monooxygenase CYP705A1**
  Failed: entities,conclusion — The paper discusses PEN1's role in DMNT biosynthesis but does not mention the entity CYP705A1.
• PMID:31758060 — ** Metabolic Cluster: The expression of PEN1 is synergistically associated with CYP705A1, forming a specialized...*
  Failed: mechanism,entities — The paper studies sweet potato volatiles and does not contain the entities PEN1 or CYP705A1.