| Starch is the major component of rice endosperm,accounting for about 80%of dry weight,and its structure and physicochemical properties play important roles in determining rice grain quality.Starch usually comprises amylopectin and amylose,and the amylose content is the key factor affecting rice-eating quality.In general,rice grains with high apparent amylose content(AAC)tend to have a hard texture and thus bad eating quality.Meanwhile,rice grain with very low AAC tends to have a sticky texture and dull endosperm.Therefore,it is necessary to screen special rice accessions and mine novel genes with appropriate AAC from the natural germplasm collection to generate novel cultivars with both good eating quality and grain transparence.In previous studies,we have generated a series of chromosome segment substitution lines(CSSLs)in the japonica rice Nipponbare background carrying the indica 9311 chromosome segment.From the CSSLs,we detected a minor QTL on chromosome 3,qAC3,for moderately increasing AC.In the present study,one CSSL line HZ1230 was crossed with the recipient parent Nipponbare(NIP)and the separate population was used to conduct the genetic linkage analysis and QTL fine mapping.Besides,the near-isogenic line(NIL)NIP(qAC3)in NIP background was generated and the effects of qAC3 on rice grain quality were investigated.The results are as follows:1.Based on the genetic linkage analysis,we found that the QTL qAC3 is a recessive locus associated with increasing AC.By using the higher backcross populations and their selfing generations,qAC3 was fine mapped to a region between the molecular markers 3AC7 and 3AC10 in Chromosome 3.The physical length between the markers 3AC7 and 3AC10 was approximately 258 kb.2.In order to investigate the effects of qAC3 locus on rice grain quality,we generated a near-isogenic line NIP(qAC3)of qAC3.The grain physiochemical characters were analyzed and the results showed that the qAC3 locus can increase grain AAC while having no significant influence on rice gel consistency(GC),gelatinization temperature(GT),and protein content.Besides,we found that the cooked rice form NIP(qAC3)has improved taste value than that of NIP.Then the starch was isolated and used for crystal structure analysis.There was no significant difference in crystallite between the two lines.And we further analyzed the starch fine structure by using GPC and HPAEC.We found that the amylose fraction(amylose short chains)as well as the amylopectin short chains(DP 6-20)increased greatly than that of NIP starch.3、The expression level of the Wx gene,as well as the GBSSI enzyme activity,were analyzed.Based on the mRNA expression level,our RT-PCR results showed that the Wx gene in the NIL(qA C3)plant has a relative higher expression level.Meanwhile,the GBSSI enzyme activity analysis exhibited the same trend that rice grain from NIP(qAC3)plant have a relative higher amount of GBSSI compared with that of NIP,which were consistent with the higher AAC result in NIP(qA C3).4、The effects of qAC3 on the physiochemical properties of rice grain under high temperature(HT)were analyzed.The results showed that there was no significant differences in rice grain appearance between HT-NIP(qAC3)and HT-NIP,however,rice from HT-NIP(qAC3)showed significant increased AAC under HT conditions.Besides,rice flour from HT-NIP(qAC3)exhibited softer GC compared with HT-NIP.What is more,the thermal characters analysis showed that rice flour from HT-NIP(qAC3)showed less sentive to HT and thus reduced GT than rice from HT-NIP.Interestingly,the grain protein content from the two lines increased greatly,however,small changes for HT-NIP(qAC3)rice grain.The starch crystal structure analysis showed that starch from HT-NIP(qAC3)gave significantly lower peak intensities than HT-NIP starch.The starch fine structure was further investigated by using GPC and HPAEC.We found starch from HT-NIP(qAC3)have increased amylose short chains and amylopectin short chains compared with NIP-HT starch. |
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