Tsuzuki, K. | bioRxiv Science

bioRxiv2024

Investigation of the isomerization of trans- and cis-cinnamic acid in Arabidopsis using stable-isotope-labeled cinnamic acid isomers

Cinnamic acid (CA) is a widely distributed metabolite in plant species and is a precursor of many important plant molecules, including lignin, flavonoids, and coumarins. CA exists as both trans and cis isomers; the trans isomer is more stable and common in nature. Previous reports have revealed that the cis isomer of CA (cis-CA) has auxin-like activity when exogenously applied. However, it has also been reported that cis-CA does not function as an auxin but affects its transport. Although these reports suggest a crucial role for cis-CA as an endogenous signaling molecule, its exact function and mechanism of isomerization from trans-CA remain unclear. Here, we report the chemical synthesis of stable-isotope-labeled trans- and cis-CA. Using these labeled compounds as internal standards, we developed a quantification method of CA using LC-MS/MS. Moreover, we monitored the endogenous conversion from trans-to cis-CA using the labeled compounds, demonstrating the UV-dependent and UV-independent CA isomerization in Arabidopsis. Additionally, we identified cis-CA in diverse plant species, including liverwort.

plant biology↗

bioRxiv2024

Radicle growth regulation of root parasitic plants by auxin-related compounds

Root parasitic plants in the Orobancheceae, such as Striga and Orobanche, cause significant damage to crop production. The germination step of these root parasitic plants is induced by host-root-derived strigolactones (SLs). After germination, the radicles elongate toward the host and invade the host root. We have previously discovered that a simple amino acid, tryptophan (Trp), as well as its metabolite, the plant hormone indole-3-acetic acid (IAA), can inhibit radicle elongation of Orobanche minor. These results suggest that auxin plays a crucial role in the radicle elongation step in root parasitic plants. In this report, we used various auxin chemical probes to dissect the auxin function in the radicle growth of O. minor and Striga hermonthica. We found that synthetic auxins inhibited radicle elongation. In addition, auxin receptor antagonist, auxinole, rescued the inhibition of radicle growth by exogenous IAA. Moreover, a polar transport inhibitor of auxin, N-1-naphthylphthalamic acid (NPA), affected radicle tropism. We also proved that exogenously applied Trp is converted into IAA in O. minor seeds, and auxinole partly rescued this radicle elongation. Our data demonstrate a pivotal role of auxin in radicle growth. Thus, manipulation of auxin function in root parasitic plants should offer a useful approach to combat these parasites.

plant biology↗