Biology subjects

Kaji, T.

Publications and source records attributed to Kaji, T..

4 recordsLinked to original sources

bioRxiv2026

MpILR1 Hydrolyzes Jasmonate-Amino Acid Conjugates to Activate dn-iso-OPDA Signaling in Marchantia polymorpha.

Jasmonates are essential phytohormones that coordinate defense responses and developmental programs across land plants. In angiosperms, the active jasmonate ligand jasmonoyl-L-isoleucine (JA-Ile), is produced through GH3-mediated conjugation of jasmonic acid to isoleucine and JA-Ile homeostasis is further shaped by ILR1/ILL-family amidohydrolases. In contrast, the primary bioactive jasmonate ligand in bryophytes, dinor-12-oxo-phytodienoic acid (dn-iso-OPDA), is inactivated through conjugation with amino acids, raising the question of whether these conjugates constitute a reversible hormone reservoir or an irreversible catabolic end point. Although the ILR1-like family has been characterized extensively for its role in auxin and jasmonate homeostasis in angiosperms, its function in bryophytes remains basically unexplored. Here we show that MpILR1, the sole Marchantia ortholog of the ILR1/ILL family, hydrolyzes a specific subset of dn-iso-OPDA-amino acid conjugates in vivo. Loss-of-function Mpilr1 mutants exhibit enhanced accumulation of dn-iso-OPDA conjugated to hydrophobic amino acids (Val, Leu and Ile) but not to hydrophilic residues (His, Glu and Gln), demonstrating substrate-selective hydrolysis. MpILR1 hydrolytic activity is required for full dn-iso-OPDA-mediated responses, including transcriptional activation and defense against gastropod herbivory. These findings establish MpILR1 as a key positive regulator of jasmonate signaling in Marchantia polymorpha and suggest that hormone conjugation/deconjugation is an ancient regulatory mechanism evolved during plant terrestrialization.

plant biology↗

bioRxiv2025

(3R, 7S)-11-hydroxy-jasmonic acid is a major oxidative shunt product of jasmonate catabolism in Arabidopsis thaliana

Jasmonoyl-L-isoleucine (JA-Ile) is a pivotal oxylipin plant hormone that regulates numerous physiological processes and stress responses. Because JA-Ile is synthesized from jasmonic acid (JA), the cellular level of JA is tightly controlled. Although the oxidative catabolism of JA to 12-hydroxy-JA (12-OH-JA) is well-characterized, the biosynthesis, accumulation dynamics, and biological functions of 11-hydroxy-JA (11-OH-JA) remain poorly understood. Here, we conducted a comprehensive investigation of 11-OH-JA in Arabidopsis thaliana, encompassing its chemical synthesis, accumulation patterns, biological activity, and biosynthetic pathways. Using chemically synthesized 11-OH-JA of naturally occurring (3R,7S)-stereochemistry, we identified 11-OH-JA as the predominant hydroxylated JA derivative that accumulates following wounding. Enzymatic assays and in silico docking studies revealed that JOX1/2/3/4 exclusively catalyze the conversion of JA to 11-OH-JA, whereas 12-OH-JA is produced by distinct pathways. Notably, the quadruple mutant joxQ completely abolished 11-OH-JA accumulation without affecting 12-OH-JA levels. Furthermore, 11-OH-JA exhibited no binding affinity for the COI1-JAZ co-receptor, indicating that it acts as a biologically inactive shunt product of JA catabolism. Our findings establish JOX-mediated 11-hydroxylation of JA as a primary inactivation pathway, separate from 12-hydroxylation. Parallel, non-redundant inactivation routes deliver layered signal termination of costly defense signals. This study provides new insights into JA catabolism, highlighting 11-OH-JA as a crucial factor in the attenuation of jasmonate signaling, and thereby redefining the framework of JA turnover in A. thaliana.

plant biology↗

bioRxiv2024

Conjugation of dn-OPDA with amino acids inhibits its hormonal bioactivity in Marchantia polymorpha

Jasmonates are important phytohormones activating plant tolerance to biotic and abiotic stress, as well as different development processes. A conserved signalling pathway activated by distinct hormones in different plant species mediates these responses: dinor-12-oxo-phytodienoic acid (dn-OPDA) isomers in bryophytes and lycophytes, and JA-Ile in most vascular plants. The final responses depend, in many cases, on the accumulation of specialized metabolites. To identify novel compounds regulated by the dn-OPDA pathway in Marchantia, untargeted metabolomic analyses were carried out in response to dn-OPDA-regulated stress. A novel group of molecules were identified as dn-OPDA-amino acid conjugates (dn-OPDA-aas), and their accumulation after wounding and herbivory confirmed by targeted metabolic profiling in Marchantia and all species in which we previously found dn-iso-OPDA. Mutants in GRETCHEN-HAGEN 3A (MpGH3A) failed to accumulate dn-OPDA-aa conjugates, and showed a constitutive activation of the OPDA pathway and increased resistance to herbivory. Our results show that dn-iso-OPDA bioactivity is reduced by conjugation with amino acids. Therefore, a dichotomous role of jasmonate conjugation in land plants is highlighted: jasmonic acid (JA) conjugation with isoleucine (Ile) produce the bioactive JA-Ile in tracheophytes, whereas conjugation of dn-iso-OPDA with different amino acids disactivate the hormone in bryophytes and lycophytes.

plant biology↗

bioRxiv2020

Complete sequences of Schizosaccharomyces pombe subtelomeres reveal multiple patterns of genome variation

Genome sequences have been determined for many model organisms; however, repetitive regions such as centromeres, telomeres, and subtelomeres have not yet been sequenced completely. Here, we report the complete sequences of subtelomeric homologous (SH) regions of the fission yeast Schizosaccharomyces pombe. We overcame technical difficulties to obtain subtelomeric repetitive sequences by constructing strains that possess single SH regions. Whole sequences of SH regions revealed that each SH region consists of two distinct parts: the telomere-proximal part with mosaics of multiple common segments showing high variation among subtelomeres and strains, and the telomere-distal part showing high sequence similarity among subtelomeres with some insertions and deletions. The newly sequenced SH regions showed differences in nucleotide sequences and common segment composition compared to those in the S. pombe genome database (PomBase), which is in striking contrast to the regions outside of SH, where mutations are rarely detected. Furthermore, we identified new subtelomeric RecQ-type helicase genes, tlh3 and tlh4, which add to the already known tlh1 and tlh2, and found that the tlh1-4 genes show high sequence variation. Our results indicate that SH sequences are highly polymorphic and hot spots for genome variation. These features of subtelomeres may have contributed to genome diversity and, conversely, various diseases.

genomics↗