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Aroma is a key grain quality trait that directly influences the market price of rice globally. Loss of function of betaine aldehyde dehydrogenase 2 (OsBADH2) affects the biosynthesis of 2‐acetyl‐1‐pyrroline (2‐AP), which is responsible for aroma in fragrant rice. The current study was aimed at creating new alleles of BADH2 using CRISPR/Cas9 gene editing technology under the genetic background of the japonica Ningjing 1 (NJ1) and indica Huang Huazhan (HHZ) varieties. Sensory evaluation and analysis using headspace solid‐phase microextraction gas chromatography–mass spectrometry (HS‐SPME‐GC‐MS) showed that the grains of the four homozygous T1 lines with new alleles of BADH2 (nj1‐cr BADH2‐1, nj1‐cr BADH2‐2, hhz‐cr BADH2‐1 and hhz‐cr BADH2‐2) produced moderate fragrance and had significantly increased 2‐AP content compared with wild‐types. Moreover, there were no significant differences in the amylose content and gelatinization temperature among the four lines with new alleles of BADH2 to the wild‐types. Thereafter, we crossed the HHZ background new alleles of BADH2 with CMS line Taonong 1A (TN1A) to produce a three‐line hybrid variety B‐Tao‐You‐Xiangzhan (BTYXZ) with increased grain aroma. The 2‐AP content in grains of the improved BTYXZ‐1 and BTYXZ‐2 reached at 26.16 and 18.74 μg/kg, and the gel consistency of BTYXZ‐1 and BTYXZ‐2 increased significantly by 9.1% and 6.5%, respectively, compared with the wild‐type Tao‐You‐Xiangzhan (TYXZ). However, the γ‐aminobutyric acid (GABA) content in the improved three‐line hybrid rice BTYXZ‐1 (5.6 mg/100 g) and BTYXZ‐2 (10.7 mg/100 g) was significantly lower than that of the TYXZ. These results demonstrated that CRISPR/Cas9 gene editing technology could be successfully utilized in improving aroma in non‐fragrant japonica and indica varieties. In addition, the newly developed BADH2 alleles provided important genetic resources for grain aroma improvement in three‐line hybrid rice.

Adjusting the sowing date is a crucial strategy for improving rice adaptability to climate change and improving grain yield. Among the quality traits of fragrant rice, the content of 2‐Acetyl‐1‐Pyrroline (2‐AP) in brown rice has garnered significant attention due to its impact on flavor and market value. The comprehensive effects of weather changes induced by adjusting the sowing date on the synthesis and accumulation of 2‐AP in fragrant rice, as well as on yield, remain unclear. We conducted a 5‐year field study in Hubei Province, China, measuring sunshine duration, temperature, and rainfall variations under six sowing dates. The research aimed to assess the comprehensive effects of these changes on the 2‐AP content in brown rice and fragrant rice yield. Delaying the sowing date resulted in shortening the rice growth duration from transplanting to heading. Early sowing (March 16) resulted in the highest rice yield, while late sowing (June 1) led to the highest 2‐AP content. Generally, with delayed sowing, the effective panicles and 1000‐grain weight increased, while the number of spikelets per panicle and grain filling rate decreased. The contents of proline, pyrroline‐5‐carboxylic acid, and γ‐aminobutyric acid exhibited a trend of initially increasing and then decreasing with delayed sowing. The 2‐AP content was significantly positively correlated with rainfall during the grain filling to maturity stage, while it showed significant negative correlations with sunshine duration, average air temperature, and the number of high temperature days (maximum air temperature ≥ 35°C) during the same stage. Since the sowing date for the highest yield differed from that for the highest 2‐AP content, we recommend early sowing to achieve optimal yield while implementing other strategies to mitigate the negative effects of prolonged sunshine duration and high temperatures during the grain filling to maturity stage on 2‐AP content. This study reveals the relationship between 2‐AP content and the yield of fragrant rice with weather factors during different growth stages, providing new insights for adjusting sowing dates to adapt to climate change in order to achieve either high yield or high 2‐AP content.

This chapter describes five‐membered heterocyclic rings of 2‐Acetyl‐1‐pyrroline, pyrrolnitrin, broussonetines, prodigiosin and undecylprodigiosin, and their fused derivatives. 2‐Acetyl‐1‐pyrroline (2‐AP) was identified as the major flavor compound in aromatic rice varieties conferring on them a “popcorn”‐like aroma. Indole‐3‐acetic acid (IAA) is the predominant naturally occurring auxin, which was identified as a plant hormone because of its ability to stimulate differential growth in response to light stimuli. Thiophene A and thiophene A diol are the major polyacetylenes isolated from the hairy root of Ambrosia maritima. β‐Pyrazole‐1‐ylalanine (βPA) is a non‐protein amino acid (isomer of histidine) first isolated from the seeds of water melon (Citrulus vulgaris). Histidine (His), like tryptophan, is an amino acid essential for protein synthesis. Thiamin (Vitamin B1), biosynthesized by most prokaryotes and eukaryotes in its active form thiamin diphosphate. Dithiolopyrrolones are a class of potent antibiotic natural products found in both Gram‐negative and Gram‐positive bacteria.