During cold acclimation in high-latitude and high-altitude regions, japonica rice develops enhanced cold tolerance, but the underlying genetic basis remains unclear. Here, we identify CTB5, a homeodomain-leucine zipper (HD-Zip) transcription factor that confers cold tolerance at the booting stage in japonica rice. Four natural variations in the promoter and coding regions enhance cold response and transcriptional regulatory activity, enabling the favorable CTB5^KM allele to improve cold tolerance. CTB5 interacts with OsHox12 and targets gibberellin (GA) metabolism genes to promote GAs accumulation in anthers and facilitate tapetum development under cold stress. Moreover, CTB5 directly regulates PYL9 and improves cold tolerance at the seedling stage by reducing reactive oxygen species (ROS) accumulation. The CTB5^KM allele is selected during the cold acclimation of japonica rice to plateau habitats in Yunnan Province. Our findings provide insights into the mechanisms underlying cold adaptation in plateau japonica rice and offer potential targets for breeding cold-tolerant rice varieties.

Summary: Yield in rice is determined mainly by panicle architecture. Using map‐based cloning, we identified an R2R3 MYB transcription factor REGULATOR OF GRAIN NUMBER1 (RGN1) affecting grain number and panicle architecture. Mutation of RGN1 caused an absence of lateral grains on secondary branches. We demonstrated that RGN1 controls lateral grain formation by regulation of LONELY GUY (LOG) expression, thus controlling grain number and shaping panicle architecture. A novel favourable allele, RGN1^C, derived from the Or‐I group in wild rice affected panicle architecture by means longer panicles. Identification of RGN1 provides a theoretical basis for understanding the molecular mechanism of lateral grain formation in rice; RGN1 will be an important gene resource for molecular breeding for higher yield.

Anthocyanins accumulate in various organs of rice, and the regulatory genes involved in pigmentation of specific organs, such as pericarp, hull, leaf, apiculus, and stigma have been elucidated. However, the corresponding gene for rice culm pigmentation has not been clarified. The well-known MYB-bHLH-WD40 (MBW) complex plays vital role in regulating the anthocyanin biosynthesis pathway in plants. However, the core members of MBW and the hierarchical regulation between these members are not fully elucidated in rice. Here, by map-based cloning, we identified the culm-specific pigmentation gene S1 whose alleles are also known for hull/pericarp pigmentation. We also clarified that one WD40 protein encoding gene, WA1, is indispensable for anthocyanin biosynthesis in rice. In the cascading regulation among MBW members, S1 (bHLH) acts as the master gene by activating the expression of C1 (MYB), and then C1 activates the expression of WA1 (WD40), which is unique in plant species. This enables MBW members to be coordinated in a common way to efficiently regulate anthocyanin biosynthesis genes. Based on these studies, we explored the minimal gene set required for anthocyanin biosynthesis in rice. These findings will help us design new rice varieties with anthocyanin accumulation in specific organs as needed.

Improvement of cold tolerance at the booting stage (CTB) in rice is a key strategy for cultivation in high-altitude and high-latitude regions. Here, we identify CTB3 gene, encoding a calmodulin-binding transcriptional activator that positively regulates cold tolerance at the booting stage in japonica rice. Two indels (57-bp and 284-bp) in the CTB3 promoter confer a differential transcriptional response to cold between the japonica and indica subspecies. OsTCP19 suppresses CTB3 expression by binding to these indels, negatively regulating cold tolerance. CTB3 activates the expression of TREHALOSE-6-PHOSPHATE PHOSPHATASE1 (OsTPP1), reducing trehalose 6-phosphate (Tre6P) levels, which increases sugar accumulation in panicles and improves cold tolerance. Additionally, favorable alleles of OsTCP19 and CTB3 are selected in japonica rice for cold adaptation. These findings highlight the important role of CTB3 in cold adaptation and its potential for improving cold tolerance in rice breeding.