Nitrogen (N) fertilizer application ensures crop production and food security worldwide. N-controlled boosting of shoot branching that is also referred as tillering can improve planting density for increasing grain yield of cereals. Here, we report that Sugar Transporter Protein 28 (OsSTP28) as a key regulator of N-responsive tillering and yield formation in rice. N supply inhibits the expression of OsSTP28, resulting in glucose accumulation in the apoplast of tiller buds, which in turn suppresses the expression of a transcriptional inhibitor ORYZA SATIVA HOMEOBOX 15 (OSH15) via an epigenetic mechanism to activate gibberellin 2-oxidases (GA2oxs)-facilitated gibberellin catabolism in shoot base. Thereby, OsSTP28-OSH15-GA2oxs module reduces the level of bioactive gibberellin in shoot base upon increased N supply, and consequently promotes tillering and grain yield. Moreover, we identify an elite allele of OsSTP28 that can effectively promote N-responsive tillering and yield formation, thus representing a valuable breeding target of N use efficiency improvement for agricultural sustainability.

Summary: Improving rice eating and cooking quality (ECQ) is one of the primary tasks in rice production to meet the rising demands of consumers. However, improving grain ECQ without compromising yield faces a great challenge under varied nitrogen (N) supplies. Here, we report the approach to upgrade rice ECQ by native promoter‐controlled high expression of a key N‐dependent floral and circadian clock regulator Nhd1. The amplification of endogenous Nhd1 abundance alters rice heading date but does not affect the entire length of growth duration, N use efficiency and grain yield under both low and sufficient N conditions. Enhanced expression of Nhd1 reduces amylose content, pasting temperature and protein content while increasing gel consistence in grains. Metabolome and transcriptome analyses revealed that increased expression of Nhd1 mainly regulates the metabolism of carbohydrates and amino acids in the grain filling stage. Moreover, expression level of Nhd1 shows a positive relationship with grain ECQ in some local main cultivars. Thus, intensifying endogenous abundance of Nhd1 is a promising strategy to upgrade grain ECQ in rice production.

Plant amino acid transporters (AATs) regulate not only long-distance transport and reallocation of nitrogen (N) from source to sink organs, but also amount of amino acids in leaves hijacked by invaded pathogens. However, the function of AATs in plant defense responses to pathogen infection remains unknown. In this study, we found that rice amino acid transporter gene OsLHT1 was expressed in leaves and up-regulated by maturing, N starvation and inoculation of blast fungus Magnaporthe oryzae. Knockout of OsLHT1 resulted in development stage- and N supply-dependent premature senescence of leaves at vegetative growth stage. In comparison to wild type, Oslht1 mutant lines showed sustained rusty red spots on fully mature leaf blades irrespective of N supply levels. Notably, no relationship between the severity of leaf rusty red spots and concentration of total N or amino acids was found in Oslht1 mutants at different developmental stages. Disruption of OsLHT1 altered transport and metabolism of amino acids and biosynthesis of flavones and flavonoids, enhanced expression of jasmonic acid- and salicylic acid-related defense genes and production of jasmonic acid and salicylic acid, accumulation of reactive oxygen species. OsLHT1 inactivation dramatically prevented the leaf invasion of M. oryzae, the hemi-biotrophic ascomycete fungus. Overall, these results establish a module connecting the activity of amino acid transporter with leaf metabolism and defense to rice blast fungus.

Salix suchowensis is an ideal model organism for investigating nitrogen (N) transport mechanisms due to its low N-input requirements. Accurate quantification of gene expression is essential for elucidating these processes, with quantitative real-time PCR (RT-qPCR) being the preferred method. However, the identification of stable reference genes for normalization in Salix suchowensis under varying N conditions remains unresolved. In this study, thirteen commonly employed candidate reference genes were evaluated across root, stem, and leaf tissues, under four N treatments (NH₄NO₃, NH₄⁺, NO₃⁻, and N deficiency). Five genes (UBQ1, UBQ3, 18S, H2A2, and H2B2) were excluded due to poor amplification efficiency or irregular melting curves. The remaining eight genes were further assessed for expression stability using the geNorm, NormFinder, and BestKeeper algorithms. Integrated ranking via RefFinder identified EF1α, EFβ, and αTUB as the most stable reference genes. GeNorm analysis suggested that two reference genes were sufficient for reliable normalization. Validation using the N-responsive gene SsAMT1 and SsNRT2 confirmed the stability of EF1α, EFβ, and αTUB as suitable reference genes. Based on comprehensive stability assessments and experimental validation, we recommended EF1α + αTUB as optimal reference gene pairs for RT-qPCR normalization under varying N conditions. Furthermore, the consistent expression of EF1α and αTUB across nine willow genotypes highlighted their broader applicability within Salix species. This study provides valuable methodological guidance for advancing molecular research on N transport in woody perennial plants.

Cadmium (Cd) is a major environmental pollutant due to its high mobility and persistence in soils, facilitating entry into the food chain and threatening ecosystems and human health. However, the mechanisms that enable Salix species, well adapted for Cd remediation, to both tolerate and accumulate Cd remain elusive. Here, two Salix genotypes with contrasting Cd tolerance were examined under control and Cd stress using integrated physiological, transcriptomic, and metabolomic analyses of roots and leaves. The Cd-tolerant genotype (Salix suchowensis P294) maintained biomass under Cd stress, whereas the Cd-sensitive genotype (Salix sinopurpurea × Salix integra P646) showed a ~17% reduction. P294 accumulated more Cd in its stems (132.76 mg kg⁻¹) and leaves (122.25 mg kg⁻¹) than P646 (93.54 and 56.24 mg kg⁻¹). Transcriptomics responses were stronger in roots, with 896 DEGs in P294 and 462 in P646, enriched in nitrogen metabolism, phenylpropanoid biosynthesis, and metal transport, whereas only 167 and 176 DEGs were detected in leaves for P294 and P646, respectively. Metabolomics revealed more altered metabolites in roots (125 in P294, 89 in P646), mainly organic acids, amino acids, and flavonoids, compared with leaves (46 and 66). RT-qPCR validated the root-specific upregulation of key detoxification and transport genes (ABCA7, PRX72, GSTU1, GSTU4, ZIP1). These results reveal a root-centered regulatory network underlying Cd accumulation and tolerance, integrating detoxification, redox homeostasis, and structural reinforcement, as well as providing valuable targets for genetic improvement of phytoremediation efficiency.