Tiller number is highly regulated by controlling the formation of tiller bud and its subsequent outgrowth in response to endogenous and environmental signals. Here, we identified a rice mutant htd2 from one of the 15,000 transgenic rice lines, which is characterized by a high tillering and dwarf phenotype. Phenotypic analysis of the mutant showed that the mutation did not affect formation of tiller bud, but promoted the subsequent outgrowth of tiller bud. To isolate the htd2 gene, a map-based cloning strategy was employed and 17 new insertions-deletions (InDels) markers were developed. A high-resolution physical map of the chromosomal region around the htd2 gene was made using the F(2) and F(3) population. Finally, the gene was mapped in 12.8 kb region between marker HT41 and marker HT52 within the BAC clone OSJNBa0009J13. Cloning and sequencing of the target region from the mutant showed that the T-DNA insertion caused a 463 bp deletion between the promoter and first exon of an esterase/lipase/thioesterase family gene in the 12.8 kb region. Furthermore, transgenic rice with reduced expression level of the gene exhibited an enhanced tillering and dwarf phenotype. Accordingly, the esterase/lipase/thioesterase family gene (TIGR locus Os03g10620) was identified as the HTD2 gene. HTD2 transcripts were expressed mainly in leaf. Loss of function of HTD2 resulted in a significantly increased expression of HTD1, D10 and D3, which were involved in the strigolactone biosynthetic pathway. The results suggest that the HTD2 gene could negatively regulate tiller bud outgrowth by the strigolactone pathway.
SUMMARYThe phytohormone auxin plays a critical role in plant growth and development, and its spatial distribution largely depends on the polar localization of the PIN-FORMED (PIN) auxin efflux carrier family members. In this study, we identify a putative auxin efflux carrier gene in rice, OsPIN3t, which acts in auxin polar transport but is also involved in the drought stress response in rice. We show that OsPIN3t-GFP fusion proteins are localized in plasma membranes, and this subcellular localization changes under 1-N-naphthylphthalamic acid (NPA) treatment. The tissue-specific expression patterns of OsPIN3t were also investigated using a b-glucuronidase (GUS) reporter, which showed that OsPIN3t was mainly expressed in vascular tissue. The GUS activity in OsPIN3tpro::GUS plants increased by NAA treatment and decreased by NPA treatment. Moreover, knockdown of OsPIN3t caused crown root abnormalities in the seedling stage that could be phenocopied by treatment of wild-type plants with NPA, which indicated that OsPIN3t is involved in the control of polar auxin transport. Overexpression of OsPIN3t led to improved drought tolerance, and GUS activity significantly increased when OsPIN3tpro::GUS plants were subjected to 20% polyethylene glycol stress. Taken together, these results suggest that OsPIN3t is involved in auxin transport and the drought stress response, which suggests that a polar auxin transport pathway is involved in the regulation of the response to water stress in plants.
Rice is a major staple food worldwide. Making hybrid rice has proved to be an effective strategy to significantly increase grain yield. Current hybrid rice technologies rely on male sterile lines and have been used predominantly in indica cultivars. However, intrinsic problems exist in the implementation of these technologies, such as limited germplasms and unpredictable conversions from sterility to fertility in the field. Here, we describe a photoperiod-controlled male sterile line, carbon starved anther (csa), which contains a mutation in an R2R3 MYB transcription regulator of pollen development. This mutation was introduced into indica and japonica rice, and it rendered male sterility under short-day conditions and male fertility under long-day conditions in both lines. Furthermore, F 1 plants of csa and a restorer line JP69 exhibited heterosis (hybrid vigor), suggesting the feasibility of using this mutation to create hybrid rice. The csabased photoperiod-sensitive male sterile line allows the establishment of a stable two-line hybrid system, which promises to have a significant impact on agriculture.PGMS line | hybrid breeding | sugar partitioning R ice (Oryza sativa L.) is a major staple food that feeds more than one-half of the human population (1). The three-and two-line hybrid rice breeding technologies take advantage of heterosis (hybrid vigor) and have been successfully applied in many countries, leading to a more than 20% yield increase over inbred varieties (2). The three-line hybrid rice breeding system was developed in the 1970s after the revolutionary discovery of the wild abortive cytoplasmic male sterile cytoplasm (CMS-WA) for the breeding of CMS lines, which solved the problem of selfpollination in the varieties used for hybrid rice production (3). In this technology, a restorer line that contains the restorer gene(s) is used as the pollen donor to recover male fertility in F 1 plants (hybrid rice) after its cross with the CMS line (Fig. S1A). To maintain CMS, a maintainer line, which has viable pollen grains and normal seed sets, is used as the pollinator to cross with the CMS line (Fig. S1A). Although this system has been widely used for hybrid rice seed production, the requirement of a maintainer line with normal cytoplasm and a restorer line with nuclearencoded fertility restorer genes restricts breeders from exploiting more rice germplasms and complicates the procedures for generating hybrid seeds (4).As a replacement of the three-line technology, a two-line system has been developed and applied for hybrid rice seed production after the discovery of the environmentally sensitive genic male sterile lines controlled by nuclear recessive gene(s). A japonica cultivar, Nongken 58S (NK58S), was the first spontaneous photoperiod-sensitive genic male sterile (PGMS) mutant identified (5). Because indica varieties are predominant in most rice planting regions, the PGMS loci/locus in NK58S were/was introduced into indica to generate breeding cultivars, such as Peiai 64S (PA64S) and Xin'an S. These ...
Chilling injury is one of the most important limiting factors affecting rice production in temperate and high-elevation areas. In this study, 146 microsatellite markers were employed to identify quantitative trait loci (QTL) conferring cold tolerance at seedling stage (CTS) .The mapping population consisted of 193 doubled haploid (DH) lines, which derived from a cross between a cold-tolerant japonica variety (AAV002863) and a cold-sensitive indica cultivar (Zhenshan97B). Tolerance to cold was assessed by the survival percentage of seedlings after cold treatment. In a climate chamber, after treatment at 68C/108C for 7 d, the measurement was taken on the sixth day of the recovery stage at room temperature. The phenotypic distribution of the DH population approximately fitted normality with skewness and kurtosis less than 0.3, and the difference among the three repetitions was not significant. Five main effect QTLs were identified with LOD > 4.0 on chromosomes 1, 2, 8 using a composite interval mapping approach. The accumulated contribution of the five QTLs was 62.28%, and a major QTL (LOD = 15.09) was identified on chromosome 2 flanked by RM561 and RM341, which explained 27.42% of the total phenotypic variation. Four significant epistatic interactions were also detected with a total contribution of 20.14%.
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