Improved Eating And Cooking Quality Of Indica Rice Cultivar YK17 Via Adenine Base Editing Of The Waxy~a Allele Of Granule-bound Starch Synthase I(GBSS I)

Like yield,quality of cooked rice is an important aspect to consider for rice breeders.Among the world,rice consumers are now concern about quality and taste of cooked rice.Amylose content(AC)or starch content is the key determinant of eating and cooking quality(ECQ)of rice that is mostly controlled by Waxy(Wx)gene in rice.As a result of allelic variation,Waxy^b(Wx^b)allele of japonica rice produces lower AC whereas the major Waxy^a(Wx^a)allele of granule-bound starch synthase I(GBSS I)in indica rice produces higher AC,making rice hard and dry after cooking.Mostly Asian rice consumers prefer soft and fresh cooked rice.Recent work has improved ECQ of japonica rice via clustered regularly interspaced short palindromic repeats CRISPR/Cas9 and cytosine base editor(CBE)techniques to produce glutinous rice or sticky rice.However,base editing has not yet been applied to modify the Wx^a allele of indica rice that usually contain higher AC.Mostly indica cultivars reflect poor ECQ due to high AC that make rice dry and hard after cooking.Zhongjiazao17 is a high yielding,early mature,disease resistant,popular rice cultivar of China that lack in ECQ due to higher AC(>25%).Adenine base editor(ABE)contains higher editing efficiency in comparison to cytosine base editor(CBE)and CRISPR/CAS9 gene editing technique.Here,we utilized ABE tool to edit Waxy^a allele,and three different Waxy^a mutants were generated.Among the three Wx^a mutants,we got MT2mutant with improved ECQ,which have desirable AC(16.7%)and gel consistency(GC)length 77mm.This study demonstrates improvement of ECQ of indica rice and that will help rice breeders to satisfy consumers.The key results obtained from current studies are highlighted below:1?Three homozygous mutants of Waxy gene body are generated in supreme indica rice cultivar YK17 by using an adenine base editor,p H-PABE-7-esg RNA vector.Mutation efficiency was ranges from 37.5-69.23%in T₀ generation.2?MT2 mutant contain AC 16.7%and GC length was found 77mm that reflects the improved eating and cooking quality as desirable low range AC.3?We also got glutinous rice or waxy rice in MT3 mutant that contain amylose 3.4%due to glutamine to arginine conversion.Opaque appearance of grain cross section also confers the findings.4?Agronomical traits and other parameters were also checked.Grain length and width showed significant difference between the wild-type YK17 and three mutants.5?We checked the mutants in hygromycin media and only transgene free mutants were evaluated in our experiments.