Kuo-Chen Yeh

Rice (Oryza sativa L.) straw-return can improve soil carbon (C) sequestration, but its adoption in intensive rice systems is limited by short fallow periods (2-eq m⁻²), indicating that intermittent oxygen input effectively mitigated the early decomposition-related emission risk. Brittle straw also increased the concentrations of dissolved inorganic C by 14.2% and nitrate by 64.3% under AWD, suggesting enhanced mineralization and potential inorganic C stabilization. Regardless of straw type, straw return improved soil C stocks by 27.3% in sandy loam and 29.6% in silty clay loam, while also promoting macroaggregate formation. Overall, this study demonstrated that coupling brittle rice straw with AWD can reduce GHG emissions while maintaining soil C benefits, offering a promising residue management strategy for intensive rice cultivation.

Napier grass ( Cenchrus purpureus syn. Pennisetum purpureum ), a perennial C ₄ forage and bioenergy crop, exhibits strong drought resilience, yet the integrative mechanisms underlying this tolerance remain incompletely understood. This study examined physiological, hydraulic, and metabolic responses of four Napier grass cultivars under PEG-induced osmotic stress and progressive soil water deficit. Drought significantly increased the root-to-shoot ratio, indicating preferential biomass allocation to roots, which supported maintenance of shoot growth and tissue water status. All cultivars showed an approximate twofold increase in water-use efficiency (WUE) under water deficit, with cv2 and cv7 displaying superior performance. Upregulation of aquaporin genes ( PIP2;2 and PIP2;3 ) suggested active hydraulic regulation that sustained carbon assimilation under reduced transpiration. Metabolic profiling revealed pronounced root-centered osmotic adjustment, including accumulation of galactinol, myo-inositol, raffinose family oligosaccharides, proline, and several amino acids. Enhanced expression of the galactinol synthase gene confirmed activation of raffinose biosynthesis pathways. Genotypic variation highlighted cv2 as particularly drought resilient. Rapid post-stress regrowth further underscored the importance of perennial root persistence. In conclusion, drought tolerance in Napier grass arises from coordinated hydraulic resilience, osmotic adjustment, and C ₄ photosynthetic efficiency, supporting its suitability for forage and bioenergy production in water-limited environments. Significant: This study shows drought tolerance in Napier grass relies on root-driven hydraulic and metabolic regulation with efficient water-use efficiency, rather than avoidance, and that PEG responses predict field performance.

Rice roots develop aerenchyma, which transports oxygen from shoots to roots, facilitating adaptation to waterlogged conditions. This oxygen oxidizes ferrous ions into ferric compounds, forming iron plaque that mitigates iron toxicity. However, the molecular mechanisms linking aerenchyma and iron plaque formation remain poorly understood. Here we identified a rice mutant (AZ1302) defective in both aerenchyma and iron plaque formation, with the causal mutation mapped to the PHYTOENE SYNTHASE 2 (OsPSY2) gene. CRISPR–Cas9-induced psy2 mutants exhibited reduced levels of carotenoid-derived hormones, strigolactones and abscisic acid, in roots. In psy2 mutants, exogenous application of strigolactones rescued aerenchyma formation, while abscisic acid restored iron plaque deposition, providing evidence for distinct hormonal regulatory functions in the two processes. These findings revise the current understanding by dissociating the roles of aerenchyma and iron plaque formation, establishing a role for OsPSY2 in integrating hormonal signalling to drive root plasticity and offering new insights into plant adaptation under environmental stress.

Carbon fixation through the Calvin-Benson-Bassham (CBB) cycle accounts for the majority of carbon dioxide (CO ₂ ) uptake from the atmosphere. The CBB cycle generates C3 carbohydrates but is inefficient at producing acetyl–coenzyme A (CoA) (C2), which is the universal precursor for synthesizing lipids. In this work, we introduced in Arabidopsis thaliana a new-to-nature CO ₂ fixing cycle, malyl-CoA-glycerate (McG) cycle, which together with the CBB cycle forms a dual-cycle CO ₂ fixation system. This cycle can fix one additional carbon by phosphoenolpyruvate carboxylase and convert the photorespiration product, glycolate, to acetyl-CoA. Plants with the McG cycle show enhanced protein abundance in their photosystems and enhanced photosystem II efficiency. McG plants had doubled CO ₂ fixation rates under atmospheric CO ₂ , increased lipid production, pronounced growth enhancement, and tripled the seed yield.

Summary: This study investigated the mechanism of nicotianamine (NA) secretion in plants by comparing the zinc/cadmium (Zn/Cd) hyperaccumulator Arabidopsis halleri with Arabidopsis thaliana. NA, a key metal chelator, is secreted into the rhizosphere of A. halleri, but the transporter responsible for this efflux remains unidentified. Transcriptome analysis, quantitative reverse transcription polymerase chain reaction, and NA efflux assays in oocytes were used to identify and characterize candidate transporters. Transgenic A. thaliana lines with altered EFFLUX TRANSPORTER OF NA 1 (ENA1) expression were generated to assess its physiological role. NA secretion and Zn uptake were quantified using UPLC‐MS/MS and ⁶⁷Zn labeling. Promoter–GUS fusion and in situ hybridization revealed spatial expression. ENA1 was identified as a plasma membrane‐localized NA exporter with higher expression in A. halleri and Zn‐induced expression only in this species. In A. thaliana, overexpression of ENA1 enhanced NA secretion and reduced Zn accumulation and sensitivity, while knockdown of homologs suppressed NA efflux. These results support a functional role of ENA1 in NA export. ENA1 mediates root‐based NA secretion and may contribute to Zn tolerance in hyperaccumulators. Its species‐specific regulation and localization suggest an adaptive mechanism for rhizosphere metal management. This discovery advances our understanding of plant metal homeostasis and provides a molecular basis for phytoremediation and biofortification strategies.

Zn deficiency is the most common micronutrient deficit in rice but Zn is also a widespread industrial pollutant. Zn deficiency responses in rice are well documented, but comparative responses to Zn deficiency and excess have not been reported. Therefore, we compared the physiological, transcriptional and biochemical properties of rice subjected to Zn starvation or excess at early and later treatment stages. Both forms of Zn stress inhibited root and shoot growth. Gene ontology analysis of differentially expressed genes highlighted the overrepresentation of Zn transport and antioxidative defense for both Zn stresses, whereas diterpene biosynthesis was solely induced by excess Zn. Divalent cations (Fe, Cu, Ca, Mn and Mg) accumulated in Zn‐deficient shoots but Mg and Mn were depleted in the Zn excess shoots, mirroring the gene expression of non‐specific Zn transporters and chelators. Ascorbate peroxidase activity was induced after 14 days of Zn starvation, scavenging H₂O₂ more effectively to prevent leaf chlorosis via the Fe‐dependent Fenton reaction. Conversely, excess Zn triggered the expression of genes encoding Mg/Mn‐binding proteins (OsCPS2/4 and OsKSL4/7) required for antimicrobial diterpenoid biosynthesis. Our study reveals the potential role of divalent cations in the shoot, driving the unique responses of rice to each form of Zn stress.

Summary: Iron (Fe) homeostasis in plants is controlled by both transcription factors (TFs) and chromatin remodeling through histone modification. To date, few studies have reported the existence of histone modification in maintaining the Fe‐deficiency response. However, the reports that do exist shed light on various histone modifications, but knowledge of the activation mark in Fe‐deficiency response is lacking. By using a forward genetics approach, we identified a crucial allele for Fe‐deficiency response, NON‐RESPONSE TO Fe‐DEFICIENCY2 (NRF2), previously described as EARLY FLOWERING8 (ELF8) associated with an activation mark on histone modification, histone H3 lysine4 trimethylation. In the nrf2‐1 mutant, a point mutation at ELF8^T404I, exhibits impaired expression of GENERAL REGULATORY FACTOR11 (GRF11) and downstream genes in the Fe‐uptake pathway. In vivo chromatin immunoprecipitation revealed that in roots, NRF2/ELF8 is essential for the expression of GRF11 for Fe‐deficiency response, whereas in shoots, NRF2/ELF8 regulates FLOWERING LOCUS C (FLC) expression for flowering time control. In summary, a key factor, NRF2/ELF8, involved in epigenetic regulation essential for both flowering time control and Fe‐deficiency response is uncovered.