Mapping of S-b Locus for F_1 Pollen Sterility in Cultivated Rice Using PCR Based Markers

In cultivated rice ( Oryza sativa L.), F-1 pollen sterility is controlled by at least 6 loci of the F, pollen sterility genes. To map S-b, one of loci, rice variety Taichung 65 (T65) carrying S-b(j)/S-b(j) and its near-isogenic line TIST2 carrying S-b(i)/S-b(i) were used to develop the mapping population. One hundred and fifty-eight microsatellite markers were selected to survey T65 and TISL2. RM13 on chromosome 5 was found to be polymorphic between them. Cosegregation indicated that RM13 was closely linked with locus S-b. Eleven RFLP markers were selected on the corresponding region from the genetic map of Rice Genome Research Program (RGP) of Japan to convert into sequence-tagged site (STS) markers. Amplicon length polymorphism (ALP) was carried out, but none of them was found to be polymorphic between T65 and TISL2. Then PCR-based RFLP (PBR) was done using six 4-nucleotide recognizing restriction endonucleases. Polymorphism was detected when PCR products of R830STS and R2213SSTS were digested with Taq I. Genetic analysis indicated that the distance between locus S-b and markers, R830STS, RM13 and R2213SSTS were 3.3 cM (centi-Morgan), 5.2 cM and 5.5 cM, respectively. These PCR-based markers could be directly used in marker-assisted selection. The technical system combining genetic mapping and PCR-based marker-assisted selection will facilitate the development of molecular breeding.

Detection of Distorted Segregation in Genotype of Pollen Calli Derived from Hybrid F_1 of Cultivated Rice (Oryza sativa L.) Using SSR Markers

S-a, S-b and S-c are three loci for F1 pollen sterility in cultivated rice （Oryza sativa L.）. Taichung 65 （T65） is all Sj/Sj at these three loci, while its F1 pollen sterile near-isogenic lines, TISL2 （S-b）, TISL4 （S-a） and TISL5 （S-c） is Sj/Sj according to their respective sterility locus. Using SSR molecular marker to detect the segregation of the allele Si and Sj in pollen calli population induced from different hybrid F1, which have different pollen sterility locus, showed that the segregation of allele Si and Sj was distorted. The distorted direction of pollen calli population in vitro was not the same as F2 population in vivo. The quantities of pollen callus carrying Sj were much more than that of carrying Siat S-a and S-c locus, the ratio of Si and Sj were 1：4.81 and 1：1.96 respectively. But the opposite tendency was observed at S-b locus, the ratio of Si and Sj being 1：0.35. At the same time, all these results were undisturbed by either culture medium or culture period.

Analysis of Introgressed Segments in Near-isogenic Lines for F_1 Pollen Sterility in Rice (Oryza sativa)

One hundred and fifty-eight microsatellite markers showing polymorphism among parents were used to survey the introgressed segments in the 50 near-isogenic lines of F_1 pollen sterility. Two hundred and sixty introgressed segments were detected in 50 near-isogenic lines, each carrying 5.2 introgressed segments on an average. Among the 260 segments, one hundred carrying F_1 pollen sterility loci concentrated on the region of F_1 pollen sterility genes, and the remaining one hundred and sixty without F_1 pollen sterility loci distributed randomly over 12 chromosomes. Both the average number and length of the introgressed segments decreased along with the increase of backcross generations. The number of introgressed segments was less than four and the length was less than 20 cM in the near-isogenic lines after backcrossing for four or more times.

Mapping of three QTLs for seed setting and analysis on the candidate gene for qSS-1 in rice(Oryza sativa L.)

The lower seed setting is one of the major hindrances which face grain yield in rice. One of the main reasons to cause low spikelet fertility （seed setting） is male sterility or pollen abortion. Notably, pollen abortion has been frequently observed in advanced progenies of rice. In the present study, 149 BC2F6 individuals with significant segregation in spikelet fertility were generated from the cross between N040212 （indica） and Nipponbare （japonica） and used for primary gene mapping. Three QTLs, qSS-1, qSS-7 and qSS-9 at chromosomes 1, 7 and 9, respectively, were found to be associated with seed setting. The recombinant analysis and the physical mapping information from publicly available resources exhibited that the qSS-1, qSS-7 and qSS-9 loci were mapped to an interval of 188, 701 and 3741 kb, respectively. The seed setting responsible for QTL qSS-1 was further fine mapped to 93.5 kb by using BC2F7 population of 1 849 individuals. There are 16 possible putative genes in this 93.5 kb region. Pollen vitality tests and artificial pollination indicated that the male gamete has abnormal pollen while the female gamete was normal. These data showed that low seed setting rate relative to qSS-1 may be caused by abnormal pollen grains. These results will be useful for cloning, functional analysis of the target gene governing spikelet fertility （seed setting） and understanding the genetic bases of pollen sterility.

Perennial aneuploidy as a potential material for gene introgression between maize and Zea perennis

Hybridization,which allows for gene flow between crops,is difficult between maize and Zea perennis.In this study,we aim to initiate and study gene flow between maize and Z.perennis via a special aneuploid plant（MDT） derived from an interspecific hybrid of the two species.The chromosome constitution and morphological characters of MDT as well as certain backcross progenies were examined.Results from genomic in situ hybridization（GISH） indicate that aneuploid MDT consisted of nine maize chromosomes and 30 Z.perennis chromosomes.The backcross progenies of MDTxmaize displayed significant diversity of vegetative and ear morphology;several unusual plants with specific chromosome constitution were founded in its progenies.Some special perennial progeny with several maize chromosomes were obtained by backcrossing MDT with Z.perennis,and the first whole chromosome introgression from maize to Z.perennis was detected in this study.With this novel material and method,a number of maize-tetraploid teosinte addition or substitution lines can be generated for further study,which has great significance to maize and Z.perennis genetic research,especially for promoting introgression and transferring desirable traits.

POLLEN STERILITY,a novel suppressor of cell division,is required for timely tapetal programmed cell death in rice

Timely programmed cell death(PCD) of the tapetum supplying nutrients to microspores is a prerequisite for normal pollen development.Here we identified a unique mutant of rice(Oryza sativa L.),pollen sterility(post),which showed aborted pollens accompanied with extra-large husks.Due to failure of timely PCD of tapetal cells,post exhibited abnormal pollen wall patterning and defective pollen grains.By map-based cloning,we identified a causal gene,POST,encoding a novel protein which is ubiquitously localized in cells.RNA in situ hybridization showed that POST is highly detected in the tapetum and microspores at stages 8 and 9.Transcriptome analysis indicated that POST could function as an important regulator of the metabolic process involved in tapetal PCD.Compared with wild-type rice,post mutant has an increased cell number resulting from elevated expression of cell cycle associated genes in grain husks.Overexpression of POST inhibits grain size in wild type,while appropriate expression of POST in post mutant can recover the seed fertility but has little effect on the large grains,illustrating that fine-tuning of POST expression could be a potential strategy for rice yield improvement.The connection between cell division and cell death conferred by POST provides novel insights into the understanding of the tapetal PCD process.

Long non-coding RNAs play an important role in regulating photoperiod-and temperature-sensitive male sterility in rice

Rice(Oryza sativa L.)is a major food crop for more than half of the world’s population.Therefore,increasing rice production is of great importance.The successful development of hybrid rice in the 1970s was an important achievement for increasing yield potential,since hybrid rice varieties produce higher yields than inbred varieties(Cheng et al.,2007).In plants,male sterility refers to the inability of producing dehiscent anthers and functional pollen(Chen and Liu,2014).