The Effects Of SLG7 Variation On Rice Grain Quality

Rice is one of the most important food crops in the world.With the improvement of people’s living standard,the demand for rice quality is higher and higher while ensuring the yield.As an important agronomic trait of rice,grain shape not only affects grain weight,one of the three factors of rice yield,but also has large effects on rice appearance quality.In our laboratory,we previously mapped and cloned SLG7,a key gene controlling rice grain shape,using a backcross population derived from Azucena and 9311.Previous studies showed that the near isogenic line carrying SLG7 not only produced slender grains,but also had excellent appearance quality.In order to further explore the effects of SLG7 gene on rice quality,we developed the CRISPR/Cas9 mutants of SLG7 under Nipponbare and Suken 118(SK118)backgrounds,respectively.SK118 is a high-yield variety in Jiangsu Province.Moreover,overexpression lines of SLG7 driven by maize Ubiqutin(Ubi)promoter were also constructed.Then,the effects of SLG7 on appearance quality,eating and cooking quality of rice were investigated.The main results are as follows:1.The SLG7 gene was edited in Nipponbare and SK118 backgrounds based on a CRISPR/Cas9 system.We obtained two homozygous mutants(nslg7-1 and nslg7-2)under the background of Nipponbare and four homozygous lines(sslg7-1-1 sslg7-1-2,sslg7-2-1 and sslg7-2-2)under the background of SK118,based on the sequencing data.2.We constructed the overexpression vector of SLG7 gene under the control of maize Ubi promoter.The construct was introduced into Nipponbare and SK118,and several homozygous overexpression lines were obtained.Two(nOE-1 and nOE-2)and three(sOE-1,sOE-2 and sOE-3)homozygous lines used for further analysis,respectively.Quantitative real-time PCR analysis showed that the expression levels of SLG7 gene were significantly increased in these transgenic lines compared with the wild type.3.Several yield traits of transgenic lines were measured in 2020.Compared with the wild type,the knocked-out mutants showed depressed plant height,shorter and rounded grains.By contrast,the overexpression lines of SLG7 gene showed increased plant height and generated slender grains.However,there were no significant changes in 1000-grain weight,grain yield per plant,tiller number and panicle length.4.The appearance quality of wild-type and transgenic lines was measured.We found that the chalkiness degree and chalkiness grain percentage of SLG7 mutants increased;The chalkiness degree and chalkiness grain percentage of overexpressed lines decreased.Therefore,SLG7 gene improves appearance quality in rice.5.Compared with the wild type,the apparent amylose content(AAC)of knock-out mutant of SLG7 significantly increased.However,the ACC of SLG7 overexpression lines significantly increased.Gel consistency(GC)showed the opposite trend.The grain protein content(PC)raised in the SLG7 mutant and declined in the overexpression lines,respectively.Totally,SLG7 had a little effect on taste value in rice.