Variation of rate of exserted stigma in P(T) GMS lines of rice

Rate of exserted stigmas (RES), ie. the ratio of glumes with exserted stigmas to the total glumes is one of the most important characteristics which affects the out-crossing rate of its combinations. Sixteen P(T) GMS lines with different ecotypes were used to study the variations of RES during their stable sterile period in Wuhan from 1992—1993. Ten healthy panicles were randomly selected at full anthesis. Their colour and the number of glumes showing one-side or two-side exserted of stigmas were investigated. Table 1 showed that there were a great variations of RES among the 16 lines tested in two consecutive years (c.v.=43.38%) and among the

Observation on Flowering Habit of Reverse Genic Sterile Rice FHS

[Objective] This study was to use reverse genic male sterile FHS better in field production. [Method] Low energy nitrogen ion beam was taken as a mutation source to conduct mutagenic treatment for indica rice 99-02 and the mutant FHS with special fertility that was isolated from their offspring. Some characteristics such as flowering habit and stigma exsertion rate of FHS were observed in this experiment. [Result] The reverse genic sterile rice FHS had an obvious peak flowering stage from 10:00 to 10:30, while the second peak flowering was from August 5 to August 10. Compared with PA64S, FHS flowered early and its flowering time was concentrated, showing that it is for seed propagation. The stigma exsertion rate of FHS was 85.8% and low exsertion rate was good for the purity of seed. [Conclusion] The reverse genic sterile rice FHS had good value in use, besides, it could also be used as comparison material for studying fertility alternation mechanism of photoperiod sensitive genic male sterile rice.

Enclosed stigma contributes to higher spikelet fertility for rice(Oryza sativa L.) subjected to heat stress

With global warming, rice plants may be subjected to heat stress more regularly during the heatsensitive flowering stage, causing spikelet sterility and grain yield loss.Stigma exsertion is considered to increase pollen reception and promote female reproductive success.The aim of this study was to investigate the role of stigma exsertion on spikelet fertility at high temperatures.Five rice cultivars(Liangyoupeijiu, Shanyou 63, Huanghuazhan, Nagina 22, and IR64) with differing degrees of stigma exsertion were cultivated and exposed to high temperature at anthesis.Heat-tolerant cultivars did not always show a high percentage of spikelets with exserted stigmas, and vice versa.Irrespective of the presence of more pollen grains on exserted stigmas, spikelets with exserted stigmas did not show greater spikelet fertility than spikelets with fewer exserted stigmas or hidden stigmas under heat stress.GA3 application augmented the percentage of spikelets with exserted stigmas;however, it did not increase spikelet fertility under heat stress.Spikelet fertility of whole panicles was negatively correlated with the percentage of spikelets with exserted stigmas, but positively with that with hidden stigmas.Viability of the hidden stigmas was less reduced than that of exserted stigmas under heat stress, suggesting that hidden stigmas have an advantage in maintaining viability.Heat stress delayed anther dehiscence and reduced the viabilities of both exserted stigmas and pollens, thereby causing low spikelet fertility.Together, these results suggest that high spikelet fertility does not depend on stigma exsertion and that enclosed stigma generally contributes to higher spikelet fertility and heat tolerance under high-temperature conditions during flowering in rice.

Identification of a major quantitative trait locus and its candidate underlying genetic variation for rice stigma exsertion rate

Stigma exsertion in male sterile lines of hybrid rice is important for seed yield.In the present study, ZS616 [Oryza sativa subsp.Xian(indica)], a male sterile line with a stigma exsertion rate(SER) as high as 94.5%, was crossed to DS552, a japonica line with almost no exserted stigmas.F3 plants with extremely low and high SER were sequenced to identify SER-associated quantitative trait loci(QTL).A major QTL for SER, qSER-3.1, was identified along with other QTL on chromosome 3 in a 3.9 Mb region.A total of 307 nonsynonymous single-nucleotide polymorphisms(SNPs) and 27 frame-shift insertion/deletions(InDels)differentiating ZS616 and DS552 were identified in the region containing qSER-3.1.Most SNPs(294) and InDels(25) were excluded after further analysis because they were shared by ZS616 and low(<2.0%) SER accessions in the Huazhong Agricultural University(HAU) core rice collection.Association analysis using the full HAU collection identified a 17-bp InDel in OS03 G0689400 as the most likely causal genetic variant underlying qSER-3.1.ZS616-type accessions(n = 54, with the 17-bp insertion) in the HAU collection had minimum(16.5%)and mean(39.6%) SERs significantly greater than those(n = 424) without the insertion(with minimum and mean SERs of 0.2% and 20.6%, respectively).Thus, this study identified a major QTL for stigma exsertion and revealed the mutation in a candidate gene for the QTL.

Fine Mapping of QTLs for Stigma Exsertion Rate from Oryza glaberrima by Chromosome Segment Substitution

Stigma exsertion is an important trait for outcrossing ability in rice.Stigma exsertion rate(SER)of male sterile lines(MSLs)is a key factor affecting F1-seed production in hybrid rice.In this study,seven QTLs for SER were detected on five chromosomes using a set of single-segment substitution lines(SSSLs)derived from O.glaberrima.Three of the QTLs were mapped in the estimated intervals of 92.5–333.0 kb.qSER-5 was located in a substitution segment of 92.5 kb.qS ER-1 b and qS ER-8 b were respectively limited to 333.0 kb and 107.5 kb by secondary substitution mapping.qSER-1 b and qSER-3 had bigger additive effects of 11.5%and 11.9%,respectively,while the other five QTLs had smaller additive effects from 5.7%to 8.6%.Open reading frames were identified in the regions of qS ER-5 and qSER-8 b in O.sativa and O.glaberrima genomes.Fine mapping of the QTLs laid a foundation for the cloning of genes,and QTLs for SER will be used to develop MSLs with strong ability of outcrossing.

Genetic mapping of quantitative trait loci for the stigma exsertion rate in rice(Oryza sativa L.)

The efficiency of hybrid rice seed production can be improved by increasing the percentage of exserted stigmas. To identify quantitative trait loci （QTLs） for this trait, we conducted QTL mapping using 75 chromosome segment substitution lines （CSSLs） developed from a cross between the donor parent, Xieqingzao B （XQZB）, a maintainer line which has high stigma exsertion and the recurrent parent, Zhonghui 9308 （ZH9308）, a restorer line which has low stigma exsertion. Atotal of nine QTLs （qSSE5, qSSE10, qSSE11, qDSE10, qDSE11, qTSE5, qTSE6, qTSE10, and qTSE11） for single stigma exsertion （ssE）, dual stigma exsertion （DSE） and total stigma exsertion （TSE） were assessed in two environments （Hainan and Zhejiang）. Six of these QTLs （qSSE10, qSSE11, qDSE10, qDSE11, qTSE10, and qTSE11） were found in both environ- ments, while one QTL （qTSE6） was found in only Hainan, and two QTLs （qSSE5 and qTSE5） were found in only Zhejiang. The qSSE10, qSSE11, qDSE10, qDSE11, qTSE6, qTSE10, and qTSE11 alleles, which are derived from the parent XQZB, exhibited a positive additive effect. In contrast, the qSSE5 and qTSE5 alleles, which are derived from the parent ZH9308, exhibited a negative additive effect. The SSE, DSE and TSE traits were significantly correlated with each other in an en- vironmentally dependent manner. These results indicated that the lines showing higher values for SSE were more likely to exhibit increased values for DSE, which would ultimately increase TSE. To evaluate the advantage of exserted stigmas for cross-pollination, single, dual and total stigma exsertion should be considered separately in future attempts at genetic improvement to achieve increased production of rice hybrid seeds. This study also provides information for fine mapping, gene cloning and particularly marker-assisted selection （MAS）, on the latter and with an emphasis the phenotypic effects and implications of the QTLs for practical use in hybrid rice breeding.

Genetic Improvement and Biological Characteristic Analysis of Dwarf Abortive TypeJaponicaCMS Lines with Wide Compatibility

From the view of methodology for genetic improvement ofJaponicacytoplasmic male sterile(CMS) lines,we introduced the breeding process of the dwarf-abortive type(DA type)JaponicaCMS line Chunjiang 95A with wide compatibility,and further investigated the biological characteristics of the DA type Chunjiang 95A and its isonuclear alloplasmic CMS line Dian-I type Chunjiang 95A.The results show that DA type Chunjiang 95A is a japonicalinous CMS line and mainly typical abortive,which is better in fertility stability than stained abortive typeJaponica CMS lines.The DA type Chunjiang 95A is featured with high stigma exsertion,good flowering habit,high outcrossing rate and wide compatibility.Its recoverability differs from stained abortive typeJaponicaCMS lines.Moreover,we discussed genetic improvement of the typical abortive type JaponicaCMS lines and the application prospects of heterosis.

Elongation of the Uppermost Internode for Changxuan 3S,a Thermo-Sensitive Genic Male Sterile Rice Line

Changxuan 3S, a thermo-sensitive genic male sterile （TGMS） rice line with eui gene, is derived from the TGMS rice line Pei＇ai 64S by irradiation with 350 Gy of ^60Co γ-ray. To elucidate the uppermost internode elongation of the TGMS line with eui gene, Changxuan 3S and its parent Pei＇ai 64S were used to study the effects of temperature on panicle exsertion. At 24℃, the uppermost internode of Changxuan 3S elongated the fastest from the 4^th day before flowering to 0 day （flowering）, being 2.1-fold as that of Pei＇ai 64S, whereas it elongated slowly during the 12^th day to the 4^th day before flowering and the 1^st to the 3^rd day after flowering. The uppermost internode of Changxuan 3S exserted from the flag leaf sheath at 22℃, 24℃ and 26℃, and the length of elongated uppermost internode increased with the decreasing temperatures. At 28℃, though the panicles of Changxuan 3S were still enclosed in the leaf sheath, the degree of panicle enclosure was significantly lower compared with Pei＇ai 64S. Cytological studies on Changxuan 3S showed that the uppermost internode elongation was attributed to the increase of cell number and cell elongation, and the latter was more significant. Moreover, the numbers of outermost and innermost parenchyma cells and the cell length of the uppermost internode reduced with the increasing temperatures.

Thermo-sensitive genic male sterile (TGMS) rice line developed by population improvement

In this study population improvement or random polycross plus mass selection was adopted with using N8S, Huaizao4, Xiang2B and Zaoyoul as parents. To help comprehensively improve the important characters such as combining ability, grain quality, resistance, stigma exsertion rate, etc. The stigma exsertion rate of ZhunS, an elite TGMS line, is 78.6%, 72.4% higher than that of V20A. Hybrids produced by crossing ZhunS with R402, Minhui77 and Minhui63 increased the yield by 3.8%-5.8% and decreased grain chalkiness by 82.1%-84.4% compared with those from crossing V20A with the corresponding R lines.

OsWRKY78 regulates panicle exsertion via gibberellin signaling pathway in rice

Panicle exsertion is one of the crucial agronomic traits in rice(Oryza sativa).Shortening of panicle exsertion often leads to panicle enclosure and severely reduces seed production.Gibberellin(GA)plays important roles in regulating panicle exsertion.However,the underlying mechanism and the relative regulatory network remain elusive.Here,we characterized the oswrky78 mutant showing severe panicle enclosure,and found that the defect of oswrky78 is caused by decreased bioactive GA contents.Biochemical analysis demonstrates that OsWRKY78 can directly activate GA biosynthesis and indirectly suppress GA metabolism.Moreover,we found OsWRKY78 can interact with and be phosphorylated by mitogen-activated protein kinase(MAPK)kinase OsMAPK6,and this phosphorylation can enhance OsWRKY78 stability and is necessary for its biological function.Taken together,these results not only reveal the critical function of OsWRKY78,but also reveal its mechanism via mediating crosstalk between MAPK and the GA signaling pathway in regulating panicle exsertion.

Genome-wide Association Analyses Reveal the Genetic Basis of Stigma Exsertion in Rice

Stigma exsertion, a key determinant of the rice mating system, greatly contributes to the application of heterosis in rice. Although a few quantitative trait loci associated with stigma exsertion have been fine map- ped or cloned, the underlying genetic architecture remains unclear. We performed a genome-wide associ- ation study on stigma exsertion and related floral traits using 6.5 million SNPs characterized in 533 diverse accessions of Oryza sativa. We identified 23 genomic loci that are significantly associated with stigma exsertion and related traits, three of which are co-localized with three major grain size genes GS3, GW5, and GW2. Further analyses indicated that these three genes affected the stigma exsertion by controlling the size and shape of the spikelet and stigma. Combinations of GS3 and GW5 largely defined the levels of stigma exsertion and related traits. Selections of these two genes resulted in specific distributions of floral traits among subpopulations of O. sativa. The low stigma exsertion combination gw5GS3 existed in half of the cultivated rice varieties; therefore, introducing the GW5gs3 combination into male sterile lines is of high potential for improving the seed production of hybrid rice.