Kanagawa University

Indole-3-butyric acid (IBA)-derived compounds, methyl 2-hydroxy-5-(1H-indole-3-yl)-pentanoate (JAX-44) and its acid derivative (JAX-77), emerge as potent modulators of root architecture, exhibiting significant growth-promoting activity for lateral and adventitious roots. Crucially, unlike native IBA, which often inhibits primary root elongation at higher concentrations, JAX-44 and JAX-77 maintain primary root length while substantially increasing lateral root numbers, thereby optimizing the plant's overall root system. Mass spectrometry analyses in Arabidopsis thaliana elucidated their mechanism: JAX-44 undergoes in vivo conversion to IBA via enzymatic hydrolysis to JAX-77, followed by oxidation to a keto-acid intermediate and finally YUCCA-mediated oxidative decarbonylation. This conversion process specifically requires an N-unsubstituted indole structure. Conversely, N- or O-methylation of JAX-44, yielding compounds JAX-86 and JAX-83, switches their activity from promotion to selective inhibition of lateral root formation. This inhibitory effect is attributed to the methylation preventing the necessary oxidative decarbonylation pathway. These results suggest that JAX-44 and JAX-77 are not only potentially superior plant growth regulators with enhanced flexibility and optimized root development for practical use but also valuable chemical biology tools that provide insight into auxin biology and the specific structural requirements for IBA bioactivity.

Oxy-hydroxides represent potential proton carriers for solid acid catalysts and proton conductors owing to their hydroxide-rich compositions. However, their applications in high-temperature environments are limited due to thermal instability associated with dehydration at moderate to high temperatures. Therefore, the development of oxy-hydroxides with enhanced thermal stability is of critical importance. Herein, we report the discovery of a strontium-gallium oxy-hydroxide, Sr₂Ga₃O₆(OH), with exceptional thermal stability. The Sr-Ga oxy-hydroxide was successfully synthesized via an unconventional synthesis route, "vapor hydroxidation", involving high-temperature heat treatment in highly concentrated water vapor. Structural characterization employing X-ray diffraction, neutron diffraction, and transmission electron microscopy revealed that the Sr-Ga oxy-hydroxide crystallizes in a trigonal structure (R3̅ space group) with lattice parameters a = 18.1904(2) Å and c = 7.2693(1) Å. Notably, OH^- anions are nonuniformly distributed within the crystal structure and are confined to a narrow space between two strontium sites. Thermogravimetry combined with desorption gas analysis indicated that OH^- anions are retained in the crystal structure up to approximately 850 °C. In situ infrared spectroscopy upon heating demonstrated proton redistribution via multilinked hydrogen bonds at elevated temperatures, which likely contributes to the excellent thermal stability.

Cuscuta, a genus of stem-parasitic plants, requires specific light and touch stimuli for host recognition and haustorium formation. Blue and far-red light promote parasitism, while red light inhibits it, but the roles played by light-responsive genes in the early stages of Cuscuta parasitism remain largely unexplored. This study utilized an in vitro C. campestris haustorium induction system to investigate this issue. RNA-sequence analysis revealed a group of differentially expressed genes that responded to the initiation of haustorium formation. Genes associated with light-signaling pathways, including phytochromes (PHYs), phytochrome-interacting factors (PIFs), and homeodomain-leucine zipper I/II transcription factors, were specifically up or downregulated in plants exposed to light for 4 h. Phylogenetic analysis demonstrated that two distinct forms of the PHYB gene, CcPHYB1 and CcPHYB2, were present in all sequenced Cuscuta species. CcPHYB2 was not expressed under normal light conditions, but was specifically upregulated under light regimes inducing haustorium formation; by contrast, CcPHYB1 exhibited non-light-dependent expression. Furthermore, the induction of haustorium formation by far-red light was canceled by red light exposure but could be re-activated by subsequent re-exposure to far-red light. The levels of expression of CcPHYB2, CcPIF1, CcPIF4, CcHOMEOBOX FROM ARABIDOPSIS THALIANA 3 (CcHAT3), CcHOMEOBOX 2 (CcHB2) and CcHB13 varied under different haustorium-inducing light conditions. Expression of these genes altered significantly upon exposure to blue and far-red light, but these changes were reversed in plants exposed to red light. These findings highlight the pivotal role of light-responsive signaling during the early stages of parasitism, providing valuable insights into the molecular mechanisms and evolution of light-mediated host recognition and parasitism in Cuscuta species.