Identification of Rice Accessions Having Cold Tolerance at the Seedling Stage and Development of Novel Genotypic Assays for Predicting Cold Tolerance.

Rice is susceptible to cold stress at the seedling stage, which can delay growth and decrease yield. We evaluated 187 rice accessions for cold tolerance at the seedling stage and developed genotypic assays for three markers. All japonica (20/20) and 20/140 indica accessions were highly cold tolerant. Two SNP markers specific for COLD1 and LOC_Os10g34840 were practical to use by normal agarose gel. The SNP marker specific for COLD1 was highly specific for predicting cold tolerance. However, the sensitivity of this marker was low as several cold-tolerant indica accessions lacked the cold-tolerant allele. The LOC_Os10g34840 marker was slightly more sensitive than the COLD1 marker for predicting highly cold-tolerant accessions. An insertion/deletion variant in the NAC6 gene was identified as a novel cold tolerance marker. The NAC6 marker predicted more highly cold-tolerant accessions compared with the other two markers. The SNP marker specific for LOC_Os10g34840 and the NAC6 marker were present in several tested subgroups, suggesting their wide effects and distribution. The three markers combined predicted the most highly cold-tolerant accessions, indicating that the marker combination is superior for applications such as marker-assisted breeding. The cold-tolerant accessions and the genotypic marker assays will be useful for future rice breeding.

RNA Sequencing Reveals Rice Genes Involved in Male Reproductive Development under Temperature Alteration.

Rice (Oryza sativa L.) is one of the most important food crops, providing food for nearly half of the world population. Rice grain yields are affected by temperature changes. Temperature stresses, both low and high, affect male reproductive development, resulting in yield reduction. Thermosensitive genic male sterility (TGMS) rice is sterile at high temperature and fertile at low temperature conditions, facilitating hybrid production, and is a good model to study effects of temperatures on male development. Semithin sections of the anthers of a TGMS rice line under low (fertile) and high (sterile) temperature conditions showed differences starting from the dyad stage, suggesting that genes involved in male development play a role during postmeiotic microspore development. Using RNA sequencing (RNA-Seq), transcriptional profiling of TGMS rice panicles at the dyad stage revealed 232 genes showing differential expression (DEGs) in a sterile, compared to a fertile, condition. Using qRT-PCR to study expression of 20 selected DEGs using panicles of TGMS and wild type rice plants grown under low and high temperature conditions, revealed that six out of the 20 selected genes may be unique to TGMS, while the other 14 genes showed common responses to temperatures in both TGMS and wild-type rice plants. The results presented here would be useful for further investigation into molecular mechanisms controlling TGMS and rice responses to temperature alteration.