PAOx can refer to phenylacetaldoxime, an important compound in plants. In plants, phenylacetaldoxime serves as a metabolic precursor for various defense compounds like cyanogenic glycosides, glucosinolates, and volatile nitriles [1]. It is also involved in auxin biosynthesis, as it can be converted to phenylacetic acid (PAA) [2,5]. The gene encoding polyamine oxidase (also denoted as PAOX) is part of the polyamine catabolism pathway in mammalian cells, generating hydrogen peroxide [3].

In plants, studies on Tococa quadrialata (recently renamed Miconia microphysca) showed that leaf herbivory leads to the accumulation of phenylacetaldoxime glucoside (PAOx-Glc), with two cytochrome P450 enzymes (CYP79A206 and CYP79A207) and a UDP-glucosyltransferase (UGT85A123) involved in its formation [1]. Another P450 (CYP71E76) converts PAOx to the volatile defense compound benzyl cyanide [1]. Robotic mechanical wounding of T. quadrialata also induced PAOx and PAOx-Glc accumulation, similar to herbivory, suggesting tissue damage triggers their production [4]. In Plumeria rubra, the gene PrCYP79D73 catalyzes the formation of (E/Z)-PAOx, which is an intermediate in the biosynthesis of floral scent compounds like 2-phenylethanol [6]. In mammalian cells, PAOX expression in fibroblasts increased matrix metalloproteinase-1 (MMP-1) secretion, degrading the extracellular matrix [3]. Also, 17β-estradiol downregulates PAOX expression via estrogen receptor 2 in MCF-7 breast cancer cells [7].

In summary, PAOx in plants is crucial for defense responses and auxin biosynthesis. In mammalian cells, PAOX in the polyamine catabolism pathway impacts processes like extracellular matrix integrity and is regulated by hormones. Understanding PAOx's functions in different organisms through these studies can provide insights into plant-herbivore interactions and mammalian cell-related pathologies.

References:

1. Müller, Andrea T, Nakamura, Yoko, Reichelt, Michael, Mithöfer, Axel, Köllner, Tobias G. . Biosynthesis, herbivore induction, and defensive role of phenylacetaldoxime glucoside. In Plant physiology, 194, 329-346. doi:10.1093/plphys/kiad448. https://pubmed.ncbi.nlm.nih.gov/37584327/

2. Perez, Veronica C, Dai, Ru, Bai, Bing, Block, Anna K, Kim, Jeongim. 2021. Aldoximes are precursors of auxins in Arabidopsis and maize. In The New phytologist, 231, 1449-1461. doi:10.1111/nph.17447. https://pubmed.ncbi.nlm.nih.gov/33959967/

3. Jeong, Hae Dong, Kim, Jin Hyung, Kwon, Go Eun, Lee, Seung-Taek. 2022. Expression of Polyamine Oxidase in Fibroblasts Induces MMP-1 and Decreases the Integrity of Extracellular Matrix. In International journal of molecular sciences, 23, . doi:10.3390/ijms231810487. https://pubmed.ncbi.nlm.nih.gov/36142401/

4. Ossetek, Kilian Lucas, Müller, Andrea Teresa, Mithöfer, Axel. 2024. Robotic mechanical wounding is sufficient to induce phenylacetaldoxime accumulation in Tococa quadrialata. In Plant signaling & behavior, 19, 2360298. doi:10.1080/15592324.2024.2360298. https://pubmed.ncbi.nlm.nih.gov/38813798/

5. Perez, Veronica C, Dai, Ru, Tomiczek, Breanna, Block, Anna K, Kim, Jeongim. . Metabolic link between auxin production and specialized metabolites in Sorghum bicolor. In Journal of experimental botany, 74, 364-376. doi:10.1093/jxb/erac421. https://pubmed.ncbi.nlm.nih.gov/36300527/

6. Dhandapani, Savitha, Jin, Jingjing, Sridhar, Vishweshwaran, Chua, Nam-Hai, Jang, In-Cheol. 2019. CYP79D73 Participates in Biosynthesis of Floral Scent Compound 2-Phenylethanol in Plumeria rubra. In Plant physiology, 180, 171-184. doi:10.1104/pp.19.00098. https://pubmed.ncbi.nlm.nih.gov/30804010/

7. Kim, Jin Hyung, Lee, Seung-Taek. 2022. Polyamine Oxidase Expression Is Downregulated by 17β-Estradiol via Estrogen Receptor 2 in Human MCF-7 Breast Cancer Cells. In International journal of molecular sciences, 23, . doi:10.3390/ijms23147521. https://pubmed.ncbi.nlm.nih.gov/35886868/