Semidwarfism is an important agronomic trait in rice breeding programs. The semidwarf mutant gene Sdt97 was previously described. However, the molecular mechanism underlying the mutant is yet to be elucidated. In this study, we identified the mutant gene by a map-based cloning method. Using a residual heterozygous line (RHL) population, Sdt97 was mapped to the long arm of chromosome 6 in the interval of nearly 60 kb between STS marker N6 and SNP marker N16 within the PAC clone P0453H04. Sequencing of the candidate genes in the target region revealed that a base transversion from G to C occurred in the 5′ untranslated region of Sdt97. qRT-PCR results confirmed that the transversion induced an obvious change in the expression pattern of Sdt97 at different growth and developmental stages. Plants transgenic for Sdt97 resulted in the restoration of semidwarfism of the mutant phenotype, or displayed a greater dwarf phenotype than the mutant. Our results indicate that a point mutation in the 5′ untranslated region of Sdt97 confers semidwarfism in rice. Functional analysis of Sdt97 will open a new field of study for rice semidwarfism, and also expand our knowledge of the molecular mechanism of semidwarfism in rice.

Coloured rice has pigments deposited in the grain pericarp; red rice is the most common type of coloured rice. Red rice is rich in essential nutrients and has been grown and consumed in China for a long time. In this study, we report the genetic characterisation and preliminary molecular mapping of a mutant gene encoding red pericarp in rice (Oryza sativa L.). To analyse the genetic basis of the red pericarp mutant, a reciprocal cross between GER-3 (red pericarp, indica cv.) and 898 (white pericarp, indica cv.) was made. The genetic analysis results confirmed that there was only one dominant gene, temporarily designated Rp (Red pericarp) controlling the segregation of the red pericarp in the F₂ population. For the molecular mapping of Rp, an F₂ population derived from an inter-subspecific cross between Gene Engineering Rice-3 (GER-3) and C418 (japonica cv., white pericarp) was constructed. The genotype of the pericarp colour of the F₂ individuals in the mapping population was validated by progeny testing of the F_2:3 families. Simple sequence repeat (SSR) markers and the bulked segregation analysis (BSA) method were used; Rp was mapped to the short arm of chromosome 7 between the SSR markers RM21182 and RM21268, with a genetic distance of 3.5 and 12.0 cM, respectively. In this paper, the potential origin of the red pericarp mutant gene Rp was also discussed.

Anthocyanin pigmentation is an important morphological marker that is commonly used to identify rice varieties and for linkage analysis. The following study investigates the genetic factors involved in the purple stigma (Ps) and purple apiculus (Pa) traits of an important indica rice cross between Zhenshan 97 (purple stigma and purple apiculus) and Minghui 63 (grey stigma and colourless apiculus). A recombinant inbred line (RIL) population derived from this cross was used for quantitative trait loci (QTL) mapping of the purple stigma and purple apiculus traits. As a result, one major QTL for the purple stigma trait, temporarily designated qPS-1-1, and one major QTL for the purple apiculus trait, temporarily designated qPA-1-1, were mapped to the short arm of chromosome 6 in the interval between the two markers Y4073L and *P. The LOD peaks of qPS-1-1 and qPA-1-1 were 44.0127 and 173.3585, respectively. In addition, qPS-1-1 and qPA-1-1 explained 66.7416% and 98.6441% of the total phenotypic variance, respectively. The Zhenshan 97 allele increased the purple stigma trait by approximately 8.0355% (for qPS-1-1) and 9.8863% (for qPA-1-1). Moreover, since qPS-1-1 and qPA-1-1 were strongly correlated, they were also located in the same vicinity of the C gene on the short arm of chromosome 6, which suggested that the two QTL might be the same. By comparing these and previous results, it was deduced that qPS-1-1 or qPA-1-1 was the C gene and was pleiotropic for both the colouration of the apiculus and the colouration of the stigma in rice.

For increasing pollination and seed set, stigma exsertion has been identified as a major component in hybrid rice. By using a recombinant inbred line (RIL) population derived from an important Indica rice cross between Zhenshan97 and Minghui63, a molecular marker-based analysis of quantitative trait loci (QTL) for stigma exsertion was performed. As a result, six prominent QTL were detected for the exserted stigma rate on chromosome 6, 2, 9, 3, 5 and 1, respectively. qSER-1-1, qSER-2-1, qSER-5-1, qSER-6-1, qSER-15-1, and qSER-18-1 explained 8.1515, 4.6657, 7.2387, 4.8997, 6.925 and 6.9291% of the total phenotypic variance, respectively. In addition, for the qSER-1-1 and qSER-2-1, the ZS97B allele increased exserted stigma rate by about 4.3484 and 3.2836%, respectively; while for qSER-5-1, qSER-6-1, qSER-15-1 and qSER-18-1, the MH63 allele increased exserted stigma rate by approx. 4.1527, 3.4243, 3.9801 and 4.0025%, respectively. Bangladesh J. Bot. 50(3): 551-556, 2021 (September)