Masanori Okamoto

Introduction: Systemic acquired resistance (SAR) is a whole-plant immune response in which localized pathogen attack primes distant tissues for enhanced defense. In Arabidopsis thaliana , this response is associated with the systemic accumulation of salicylic acid (SA), pipecolic acid (Pip), and N -hydroxypipecolic acid (NHP), but their spatial dynamics in wheat remain poorly understood. Methods: Here, we investigated the spatial dynamics of SA, Pip, and NHP accumulation in the wheat cultivar Fielder following infection with the powdery mildew fungus Blumeria graminis f. sp. tritici . Their accumulation was examined between leaves, within a single leaf, and at 1–3 cm from the infection site. Results: Infection induced strong local accumulation of all three metabolites, with NHP showing the largest response, increasing approximately 751-fold in infected primary leaves, 65-fold in the infected proximal leaf sectors, and 71-fold within infected lesions. Pip also increased markedly in infected tissues, whereas SA showed more moderate increases. These metabolic changes were accompanied by local induction of SA- and NHP-biosynthesis-related genes and pathogenesis-related ( PR ) genes. Despite the strong response at infection sites, protected distal leaves and non-infected tissues within the same leaf showed little or no accumulation of SA, Pip, or NHP. The same spatial restriction was observed for defense-related gene expression, while Bgt detection confirmed that fungal colonization was confined to infected regions. Discussion: These findings indicate that Fielder develops a strong local defense-associated metabolic response to powdery mildew infection, but corresponding accumulation of SA, Pip, and NHP was not detected in non-infected tissues at the spatial scales examined. This spatial pattern differs from the systemic accumulation described in the Arabidopsis SAR model and suggests that systemic immune signaling in Fielder may not rely on long-distance accumulation of these metabolites.

Vascular plants rapidly coordinate root and shoot responses to water stress. Abscisic acid (ABA) mediates these adaptations; however, it remains unclear which cells produce ABA, whether ABA synthesis shifts during stress, and whether ABA movement is required for its adaptive functions. Here, we map ABA biosynthesis at cellular resolution in Arabidopsis and report that water-stress adaptive responses in roots and shoots require movement of ABA and its precursor AB-aldehyde from vascular tissues to target cells. We suggest that ABA accumulation arises from two parallel routes: (i) ABA synthesized in the vasculature via ABA2 and AAO3, then moving to guard cells, and (ii) phloem-derived AB-aldehyde being converted to ABA in the epidermis or bundle sheath by AAO1 and AAO2. Finally, we predict that tightly packed cells beneath leaf veins facilitate efficient ABA delivery to guard cells, an anatomical arrangement that has enabled angiosperms to evolve the use of ABA to rapidly close stomata.

Reduction of culm length is a key breeding target in wheat to improve lodging resistance. However, only a few culm length–related genes have been used in breeding programs, and some of these genes are associated with undesirable side effects. Therefore, novel genetic variations are needed for fine regulation of culm length. In this study, we mutagenized the Japanese wheat cultivar ‘Chikugoizumi’ with γ-irradiation and characterized a mutant, CI1G0208, with a short culm and compact spike. Whole-genome resequencing and fluorescence in situ hybridization revealed a translocation of the distal region of chromosome 5A to the short arm of chromosome 2B, resulting in duplication of a 75.7-Mbp chromosome 5A fragment and a 37.8-Mbp deletion on chromosome 2B. Segregation analysis demonstrated that progeny carrying the 2BS–5AL translocation had significantly shortened culm and spike. The duplicated 5A fragment contained two known culm length–related genes, Q and Rht12, both of which showed increased expression in the mutant. Exogenous gibberellin (GA) application partially restored the culm length, indicating that both GA-dependent and GA-independent pathways contributed to the mutant phenotype and suggesting that the increased gene dosage of Q and Rht12 cooperatively reduced culm length. These findings demonstrate that an artificially induced mutation can generate a novel allele affecting an agronomically important trait and highlight the potential of such mutations as breeding resources for fine-tuning culm length.

Grain yield in wheat is frequently driven by pre-anthesis growth and how carbon is directed to reproductive parts, determining the potential size of the grain-producing sink. However, the genetic mechanisms controlling this carbon allocation remain unclear. In this study we discovered a series of loci in tetraploid and hexaploid wheats that, when combined, confer an average grain yield advantage in hexaploid winter wheat of approx. 5-7% under high-input farming while approx. 10-15% under low-input conditions. The responsible gene is GRAIN NUMBER INCREASE 2 ( GNI2 ), ancestral to its duplicate GNI1 , and represented by the homoeo-allelic series GNI-A2 , GNI-B2 , and GNI-D2 . GNI1 and all GNI2 copies additively affect floral growth and fertility by modulating reproductive allocation and harvest index. Herewith, we describe a series of grain yield-relevant GNI2 homoeo-alleles with a proven track record for being beneficial in both high- and low-input environments. Their deployment offers a sustainable pathway to raise global grain yields in the future.

Background: Abscisic acid (ABA) is a key phytohormone that regulates plant growth and stress responses through protein phosphorylation. While ABA-induced phosphosignaling has been extensively studied in Arabidopsis thaliana, its conservation and divergence across plant species remain unclear. Methods: Here, we performed phosphoproteomic analysis using LC-MS/MS in Arabidopsis, rice (Oryza sativa), and soybean (Glycine max) to compare ABA-responsive phosphorylation profiles among monocots, dicots, and legumes. Results: ABA treatments on Arabidopsis, rice, and soybean seedlings yielded approximately 24,604, 18,865, and 24,930 phosphopeptides, respectively. Comparative analyses revealed both conserved and species-specific ABA-responsive phosphoproteins. Conclusions: This work provides insights into the evolutionary diversification of ABA signaling and its potential applications in improving crop stress tolerance.

Bacterial phytopathogens, such as Pseudomonas syringae pv. tomato ( Pst ) DC3000, induce water-soaked lesions in the leaf apoplast under high humidity, facilitating infection. However, it remains largely unclear how plants regulate their resistance to restrict bacterial infection in response to humidity. Here, we demonstrate that abscisic acid (ABA)-catabolizing ABA 8’-hydroxylase, encoded by CYP707A3 , plays a critical role in this resistance in Arabidopsis thaliana . Elevated humidity induces CYP707A3 expression, which is essential for reducing ABA levels and promoting stomatal opening, thereby limiting bacterial water-soaking and infection following leaf invasion. High humidity also increases cytosolic Ca ²⁺ levels via the Ca ²⁺ channels CNGC2 and CNGC4, with partial involvement from CNGC9, activating the calmodulin-binding transcription activator CAMTA3 to drive CYP707A3 induction. However, Pst DC3000 counteracts this defense response using type III secretion effectors, including AvrPtoB, facilitating water-soaking. These findings provide insights into the mechanisms underlying the competition between plants and bacteria for leaf water under elevated humidity.

Some fungi form fairy rings by secreting fairy chemicals that regulate plant growth. Among them, 2-azahypoxanthine (AHX) has been proposed as a new phytohormone, but its mechanisms remain unclear. We treated Arabidopsis thaliana with 400 μm AHX and observed growth inhibition, contrasting with earlier reports in bentgrass. To elucidate this effect, we performed transcriptome sequencing and identified differentially expressed genes. Gene ontology enrichment revealed activation of hormone- and stress-related terms and suppression of photosynthesis-related terms. Liquid chromatography-mass spectrometry further showed an increase in 1-aminocyclopropanecarboxylic acid, an ethylene precursor, after AHX treatment. These results suggest that AHX alters the stress response in A. thaliana by regulating genes associated with multiple plant hormones, including abscisic acid, ethylene, jasmonic acid, salicylic acid, and cytokinins.

Parasitic plants have evolved specialized mechanisms to extract water and nutrients from their hosts, often causing severe agricultural losses. Striga hermonthica, a member of the Orobanchaceae family, exhibits a unique adaptation in the abscisic acid (ABA) signaling pathway, which enhances its growth efficiency during parasitism. Striga hermonthica protein phosphatase 2C (ShPP2C1) is a negative regulator of ABA signaling but, unlike typical PP2Cs, is not inhibited by PYR1-like (PYL) ABA receptors. Because of ShPP2C1, Striga hermonthica shows low ABA sensitivity and high transpiration, facilitating resource uptake from the host. To determine whether similar PP2Cs are conserved in other parasitic Orobanchaceae, we performed a phylogenetic analysis using public sequence data, revealing that ShPP2C1 is unique to the genus Striga. Furthermore, an in vitro phosphatase assay revealed specific amino acid residues responsible for disrupting the inhibition by PYLs. Structural comparisons between ShPP2C1 and Arabidopsis ABA INSENSITIVE 1 (ABI1) showed that the lack of interaction with PYLs is due to steric hindrance from a combination of amino acid substitutions. These findings provide new insight into the molecular basis of Striga's parasitic strategy.