Fragrant rice is regarded as a premium variety due to its distinctive aroma, delicate texture, and rich nutritional value. This aroma primarily originates from 2-acetyl-1-pyrroline (2-AP), but the metabolic basis of 2-AP remains elusive to this day, and the genetic basis for metabolite accumulation is largely unknown. While several researchers have investigated differences in 2-AP synthesis pathways between fragrant and non-fragrant rice, few studies have examined the 2-AP synthesis pathways in fragrant rice varieties exhibiting 2-AP differences. Therefore, after conducting gene similarity analyses on six fragrant rice varieties, we measured the expression levels of substances and related genes involved in multiple metabolic pathways within the 2-AP synthesis pathway, along with the specific enzyme activities associated with these pathways. Results indicate that XG12 (Guizhou Fragrant Rice Variety) exhibits the highest 2-AP content, yet its efficiency in synthesizing 2-AP is not the highest across any individual metabolic pathway. This finding reveals that among fragrant rice varieties, 2-AP content negatively correlates with OsBadh2 expression levels and GABA content, while showing no linear correlation with other related substances or metabolic genes. At this point, variations in the major effect gene OsBadh2 no longer dominate; instead, subtle differences in 2-AP content are jointly determined by numerous minor effect genes and environmental factors. This phenomenon not only resolves apparent contradictions but profoundly illuminates the complex regulatory mechanisms governing 2-AP biosynthesis. 2-AP synthesis represents a dynamic equilibrium process, with different fragrant rice varieties potentially accumulating 2-AP through distinct metabolic pathways. Additionally, this study analyzed the volatile organic compounds (VOCs) of six fragrant rice varieties through metabolomics. Results revealed that DLX, which exhibited the lowest 2-AP content, contained the richest array of aggregated VOCs, indicating no correlation between 2-AP and numerous VOCs. Our findings provide a clear research direction for elucidating the genetic regulatory mechanisms of 2-AP underlying fragrant rice and lay the foundation for technological research aimed at enhancing the aroma of fragrant rice varieties.

In addition to being governed by genetic factors, environmental factors also play a crucial role in influencing the fragrance of rice. In this research, the high-quality rice variety Dalixiang was selected as the experimental material to investigate the impacts of soil nutrients in Guiyang and Meitan on its fragrance. The results indicated that the levels of ammonium nitrogen, organic matter, total nitrogen, available nitrogen, and the pH value in the soil of Meitan were lower compared to those in Guiyang. Conversely, the contents of total potassium, available phosphorus, and available potassium were higher in Meitan. Specifically, the concentrations of 2-acetyl-1-pyrroline (2AP) in the leaves of Dalixiang at the heading stage and in the grains at the maturity stage at the Meitan planting site were 0.13 mg/kg and 0.56 mg/kg, respectively. These values were significantly lower than the 0.17 mg/kg and 0.64 mg/kg measured at the Guiyang planting site. This phenomenon is associated with the higher expression levels of the betaine aldehyde dehydrogenase (OsBadh2) gene, enhanced enzyme activities, and a greater content of γ-aminobutyric acid (GABA) in the leaves of Dalixiang at the Meitan planting site. In contrast, the expression levels of genes related to triose phosphate isomerase (OsTPI), proline dehydrogenase (OsProDH), ornithine aminotransferase (OsOAT), and Delta1-pyrroline-5-carboxylic acid synthetase (OsP5CS), along with their corresponding enzyme activities, as well as the contents of methylglyoxal, proline, and ornithine, were lower. In conclusion, due to the influence of the Guiyang environment, the biosynthesis of Dalixiang 2AP was promoted, which made the Dalixiang planted in Guiyang stronger than that planted in Meitan. This study provides a theoretical basis for the selection of the best planting area of Dalixiang and the improvement of Dalixiang flavor through agronomic cultivation techniques.

Rice (Oryza sativa L.) production is constantly threatened by devastating diseases such as rice blast, bacterial blight, and brown planthopper infestation. The AP2-type transcription factor OsHTR (also known as SMOS1/SHB/RAL1/NGR5/GR5) has been previously implicated in hormonal signaling networks and nitrogen use efficiency; however, its role in disease resistance remains largely unexplored. In this study, we functionally characterized OsHTR in disease resistance using knockout (KO) and overexpression (OE) transgenic lines in the ZH11 background. Transcriptome analysis revealed that differentially expressed genes in the htr mutant were significantly enriched in plant–pathogen interaction pathways, with multiple NBS-LRR and NB-ARC resistance-related genes upregulated. Real-time PCR validation confirmed the upregulation of 15 candidate resistance genes in the htr mutant. Comprehensive resistance evaluations suggested that HTR-KO lines exhibited enhanced resistance to rice blast and bacterial blight compared to wild-type ZH11 and HTR-OE lines, which displayed moderate susceptibility. In contrast, all lines remained highly susceptible to brown planthopper, indicating a disease-specific regulatory function of OsHTR. Furthermore, targeted knockout of individual upregulated resistance-related genes (LOC_Os10g04090, LOC_Os12g29690, LOC_Os02g11980, and LOC_Os11g11770) and OsHTR-interacting gene LOC_Os06g03710 confirmed their distinct contributions to blast and bacterial blight resistance but did not establish them as direct targets of OsHTR. Collectively, our results indicate that OsHTR functions as a negative regulator of disease resistance in rice, likely acting through transcriptional repression of defense-related genes, although direct binding remains to be demonstrated. This study uncovers a novel regulatory module connecting AP2-type transcription factors to disease resistance and provides valuable genetic resources for molecular breeding of broad-spectrum-resistant rice cultivars.