OsSYL2AA , an allele identified by gene-based association, increases style length in rice (Oryza sativa L.).

Stigma characteristics are important factors affecting the seed yield of hybrid rice per unit area. Natural variation of stigma characteristics has been reported in rice, but the genetic basis for this variation is largely unknown. We performed a genome-wide association study on three stigma characteristics in six environments using 1.3 million single-nucleotide polymorphism (SNPs) characterized in 353 diverse accessions of Oryza sativa. An abundance of phenotypic variation was present in the three stigma characteristics of these collections. We identified four significant SNPs associated with stigma length, 20 SNPs with style length (SYL), and 17 SNPs with the sum of stigma and style length, which were detected repeatedly in more than four environments. Of these SNPs, 28 were novel. We identified two causal gene loci for SYL, OsSYL3 and OsSYL2; OsSYL3 was co-localized with the grain size gene GS3. The SYL of accessions carrying allele OsSYL3AA was significantly longer than that of those carrying allele OsSYL3CC . We also demonstrated that the outcrossing rate of female parents carrying allele OsSYL2AA increased by 5.71% compared with that of the isogenic line carrying allele OsSYL2CC in an F1 hybrid seed production field. The allele frequencies of OsSYL3AA and OsSYL2AA decreased gradually with an increase in latitude in the Northern Hemisphere. Our results should facilitate the improvement in stigma characteristics of parents of hybrid rice.

Identification of putative markers linked to grain plumpness in rice (Oryza sativa L.) via association mapping.

BACKGROUND: Poor grain plumpness (GP) is one of the main constraints to reaching the yield potential of hybrid rice. RESULTS: In this study, the GP of 177 rice varieties was investigated in three locations across 2 years. By combining the genotype data of 261 simple sequence repeat (SSR) markers, association mapping was conducted to identify the marker-GP association loci. Among 31 marker-GP association loci detected in two or more environments and determined using general linear model (GLM) analyses, seven association loci were also detected using mixed linear model (MLM) analyses. The seven common loci detected by the two analytical methods were located on chromosomes 2, 3 (2), 7, 8 and 12 (2) and explained 7.24~22.28% of the variance. Of these 7 association loci, five markers linked to GP were newly detected: RM5340 on Chr2, RM5480 and RM148 on Chr3, RM1235 on Chr8, and RM5479 on Chr12. CONCLUSIONS: Five marker-GP association loci were newly detected using both the GLM and MLM analytical methods. Elite allele RM505-170 bp had the highest average phenotypic effect on increasing the GP, and the typical carrier variety was 'Maozitou'. Based on the distribution of the elite alleles among the carrier varieties, the top 10 parental combinations for improving the GP in rice via cross-breeding were predicted.

Transcript profiling for regulation of sweet potato skin color in Sushu8 and its mutant Zhengshu20.

Sweet potato [Ipomoea batatas (L.) Lam.] (2n = 6x = 90) is an economic important autopolyploid species and its varieties differ regarding storage root skin and flesh colors. Two sweet potato genetic lines, Sushu8 (with red skin) and its mutant Zhengshu20, which produced different colored storage roots, were used in this study. The total flavonoid, carotenoid, and anthocyanin contents of the two lines were analyzed and revealed that anthocyanin was primarily responsible for the skin color difference. In addition, the early storage root expanding stage was the key period for anthocyanin accumulation in Sushu8. A total of 24 samples, including the skins of the fibrous root and the storage root at the early and middle expanding stages as well as the flesh of the storage root at the middle expanding stage, were analyzed based on differentially expressed genes identified by transcriptome sequencing and a weighted gene co-expression network analysis. Two gene modules highly related with the regulation of sweet potato skin color through stress responses as well as starch synthesis and glucose metabolism were identified. Furthermore, the WRKY75 transcription factor gene, fructose-bisphosphate aldolase 2 gene, and other DEGs highly related to the regulation of anthocyanin metabolism were enriched in the brown and green modules.

[The correlation between panicle angle and rice quality and genetic analysis on rice quality in japonica rice (Oryza sativa L.)].

Linear correlation between panicle angle and 10 quality traits were studied by using P1, P2 and 349 lines of the RIL population in a cross of Bing 8979(erect panicle)/C bao (curve panicle) in japonica rice. We found that, there were no linear correlation between panicle angle and brown rice rate , head rice rate, chalky grain rate, chalkiness area, gelatinization temperature, gel consistency and apparent amylose content. The correlation coefficients between panicle angle and milled rice rate, between panicle angle and grain length, and between panicle angle and grain length/width ratio were 0.124*, 0.470** and 0.241** , respectively. By using major gene-polygene mixed inheritance models, genetic analyses showed that brown rice rate, milled rice rate and apparent amylose content were controlled by two major genes plus polygenes. The two major genes expressed additive effect and additive x additive effects. Head rice rate, grain length, grain length/width ratio and gel consistency were controlled by two major genes with additive-epistatic effects plus polygenes. Chalky grain rate, chalkiness area and gelatinization temperature were controlled by three major genes with additive-epistatic effects plus polygenes. Brown rice rate, milled rice rate, head rice rate, chalky grain rate, chalkiness area and gelatinization temperature traits were mainly governed by major genes. Grain length, grain length/width ratio, gel consistency and apparent amylose content traits were mainly governed by polygenes.

Favorable Marker Alleles for Panicle Exsertion Length in Rice (Oryza sativa L.) Mined by Association Mapping and the RSTEP-LRT Method.

The panicle exsertion length (PEL) in rice (Oryza sativa L.) is an important trait for hybrid seed production. We investigated the PEL in a chromosome segment substitution line (CSSL) population consisting of 66 lines and a natural population composed of 540 varieties. In the CSSL population, a total of seven QTLs for PEL were detected across two environments. The percentage of phenotypic variance explained (PVE) ranged from 10.22 to 50.18%, and the additive effect ranged from -1.77 to 6.47 cm. Among the seven QTLs, qPEL10.2 had the largest PVE, 44.05 and 50.18%, with an additive effect of 5.91 and 6.47 cm in 2015 and in 2016, respectively. In the natural population, 13 SSR marker loci were detected that were associated with PEL in all four environments, with the PVE ranging from 1.20 to 6.26%. Among the 13 loci, 7 were novel. The RM5746-170 bp allele had the largest phenotypic effect (5.11 cm), and the typical carrier variety was Qiaobinghuang. An RM5620-RM6100 region harboring the EUI2 locus on chromosome 10 was detected in both populations. The sequencing results showed that the accessions with a shorter PEL contained the A base, while the accessions with a longer PEL contained the G base at the 1,475 bp location of the EUI2 gene.