Relationship Between the First Base of the Donor Splice Site of Waxy Gene Intron 1 and Amylose Content in Yunnan Indigenous Rice Varieties

There exists a single nucleotide polymorphism, G or T, at the first base of the donor splice site of waxy gene intron 1 in rice. In order to study the relationship between the first base of the donor splice site of waxy gene intron 1 and amylose content in rice, the one-step PCR method was used to determine whether it is G or T in 220 Yunnan indigenous rice varieties from 14 districts, 55 towns/counties of Yunnan Province, and 101 varieties of which were validated by the PCR-Acc I method. According to the G/T polymorphism, 164 rice varieties showed GG-genotype, while the other 56 fell into TT- genotype, accounting for 74.5% and 25.5% of all the test varieties, respectively. When all the rice varieties were divided into indica and japonica subspecies, it was found that 80.5% of indica rice and 67.0% of japonica rice belonged to GG-genotype. The rice varieties with GG-genotype had significantly higher amylose content （18.95% on average） than those with TT- genotype （all below 16%）, but 33 rice varieties with GG-genotype still had low amylose content ranging from 3.91% to 15.93%, and most of them came from the Dai minority area in the Southwest of Yunnan Province. However, there was no significant difference in the mean amylose content of the same GG or TT genotypes between indica and japonica rice, suggesting that different genetic backgrounds, indica or japonica, had no effect on amylose content. The coefficient of correlation between the genotype and amylose content was 0.733 （P〈0.01）.

Generation of new glutinous rice by CRISPR/Cas9-targeted mutagenesis of the Waxy gene in elite rice varieties

In rice, amylose content （AC） is controlled by a single dominant Waxy gene. We used Clustered Regularly Interspaced Short Palindromic Repeats （CRISPR）/CRISPR-associated 9 （Casg） to introduce a loss-of-function mutation into the Waxy gene in two widely cultivated elite japonica varieties. Our results show that mutations in the Waxy gene reduce AC and convert the rice into glutinous ones without affecting other desirable agronomic traits, offering an effective and easy strategy to improve glutinosity in elite varieties. Importantly, we successfully removed the transgenes from the progeny. Our study provides an example of generating improved crops with potential for commercialization, by editing a gene of interest directly in elite crop varieties.

Genome-Wide Association Study of Cooked Rice Textural Attributes and Starch Physicochemical Properties in indica Rice

Rice cooking and eating qualities(CEQ)are mainly determined by cooked rice textural parameters and starch physicochemical properties.However,the genetic bases of grain texture and starch properties in rice have not been fully understood.We conducted a genome-wide association study for apparent amylose content(AAC),starch pasting viscosities,and cooked rice textural parameters using 279 indica rice accessions from the 3000 Rice Genome Project.We identified 26 QTLs in the whole population and detected single nucleotide polymorphisms(SNPs)with the lowest P-value at the Waxy(Wx)locus for all traits except pasting temperature and cohesiveness.Additionally,we detected significant SNPs at the SUBSTANDARD STARCH GRAIN6(SSG6)locus for AAC,setback(SB),hardness,adhesiveness,chewiness(CHEW),gumminess(GUM),and resilience.We subsequently divided the population using a SNP adjacent to the Waxy locus,and identified 23 QTLs and 12 QTLs in two sub-panels,WxT and WxA,respectively.In these sub-panels,SSG6 was also identified to be associated with pasting parameters,including peak viscosity,hot paste viscosity,cold paste viscosity,and consistency viscosity.Furthermore,a candidate gene encoding monosaccharide transporter 5(OsMST5)was identified to be associated with AAC,breakdown,SB,CHEW,and GUM.In total,39 QTLs were co-localized with known genes or previously reported QTLs.These identified genes and QTLs provide valuable information for genetic manipulation to improve rice CEQ.

Genetic Polymorphism of Wx Gene and Its Correlation with Main Grain Quality Characteristics in Rice

The allelic variation of the Wx gene in 50 non-glutinous rice varieties （lines） was analyzed by using the microsatellite marker RM190 [for （CT）n simple sequence repeat （SSR）] and cleaved amplified polymorphic sequence（CAPS） marker 484/W2R-ACCⅠ[for G/T single nucleotide polymorphism （SNP）]. Six homozygous （CT）n types, namely （CT）20, （CT）19, （CT）18, （CT）17, （CT）16, （CT）14, （CT）11 and （CT）10, and a heterozygous genotype （CT）11/（CT）18 were detected for RM190, of which （CT）11 and （CT）18 were predominant. Two homozygous Wx genotypes （G/G and T/T） and one heterozygous （G/T） were detected using 484/W2R-ACC Ⅰ. Most of the materials with a RM190 of （CT）11 were G/G for SNP of 484/W2R-ACC Ⅰ, while T/T for SNP was predominantly appeared in materials with （CT）18. The materials tested could be grouped into 10 categories using the two markers together. Results indicated that 59.3% variance of amylose content was attributed to the polymorphism of Wx gene revealed by RM190, while 56.1% and 24.6% of the variances in amylose content and gel consistency were respectively to the polymorphism of Wx gene revealed by 484/W2R-ACC Ⅰ. Furthermore, with both SSR and CAPS markers, 72.4% of the variance in amylose content could be explained. In addition, the application prospects of the two markers in breeding were also discussed.

Development and Substance Accumulation of Caryopsis in Transgenic Rice with Antisense Wx Gene

The development and substance accumulation of rice caryopsis were studied by using the transgenic japonica and indica rice with antisense Wx gene. The weight of caryopses in transgenic rice was lower than that in non-transgenic one, and the reduction in weight was significantly correlated to the reduction in amylose content. In caryopsis of transgenic rice, the number of endosperm cells was less than that in caryopsis of non-transgenic one, but the proliferation speed was considerably higher during the first six days after flowering （DAF）. During the first nine DAF, the soluble sugar content of transgenic rice caryopsis was less than that of the non-transgenic one, but the situation was reverse after nine DAF. Moreover, the total starch content also declined with the decrease in amylose content of transgenic rice caryopsis, while the amylopectin content increased accordingly. Therefore, the composition of starch in caryopsis also changed, but it did not affect the accumulation of protein in transgenic rice caryopsis.

A Cleaved Amplified Polymorphic Sequence Marker to Detect Variation in Wx Locus Conditioning Translucent Endosperm in Rice

The translucent endosperm trait in a japonica rice variety ＇Kantou 194＇ is controlled by a Wx-mq gene which is allelic to Wx locus by genetic analysis and allelic test. The amylose content analysis showed that an intermediate amylose content between those of glutinous and non-glutinous rice existed in endosperm of homozygous Wx-mq genotype. The slight changes of amylose content in different varieties and F1 grains with an identical Wx-mq genotype might be influenced by dissimilar genetic background. To identify the Wx-mq genotype simply and rapidly, a cleaved amplified polymorphic sequence （CAPS） marker was designed. The result from the molecular detection indicated that it could be used for marker-assisted selection for low amylose content varieties in rice breeding.

Identification of Multiple Alleles at the Wx Locus and Development of Single Segment Substitution Lines for the Alleles in Rice

The microsatellite markers 484/485 and 484/W2R were used to identify the multiple alleles at the Wx locus in rice germplasm. Fifteen alleles were identified in 278 accessions by using microsatellite class and G-T polymorphism. Among these alleles, （CT）12-G, （CT）15-G, （CT）16-G, （CT）17-G, （CT）18-G and （CT）21-G have not been reported. Seventy-two single-segment substitution lines （SSSLs） carrying different alleles at the Wx locus were developed by using Huajingxian 74 with the （CT）11-G allele as a recipient and 20 accessions containing 12 different alleles at the Wx locus as donors. The estimated length of the substituted segments ranged from 2.2 to 77.3 cM with an average of 17.4 cM.