Cloning And Functional Analysis Of Maize Endosperm Modifier Su2

Maize is the world’s largest crop and a vital source of food,feed and industrial products.Compared with rice,wheat and other food crops,the lack of two essential amino acids（lysine and tryptophan）in its storage protein seriously affects the quality balance of maize protein.Q uality Protein Maize（QPM）significantly improved protein nutritional quality by using o2 mu tant as lysine donor,and modified the o2 mutant floury endosperm into vitreous endosperm b y endosperm modifier.Since the breeding of high-quality protein maize,it has been introduce d into 23 countries in South America,Asia and Africa,and has been widely promoted and use d,and important progress has also been made in the breeding field in our country.However,t he number of endosperm modifiers that have been cloned is relatively small,and the modifica tion mechanism of the transformation of powdery endosperm into hard endosperm is still uncl ear.In this study,a quality protein maize inbred line CM105mo2,K0326Y was used to constr uct a CM105mo2×K0326Y F₂ population,and map-based cloning into a quality protein maize（QPM）modifier—Sugary2（Su2）,which encodes starch synthase SSIIa.The modification fun ction of Su2 was further verified by linkage analysis and allelic hybridization test,and maize kernels with hard endosperm in the o2 background were obtained.Compared with K0326Y,s u2 has a higher degree of vitreous modification as a modifier.The modification mechanism of endosperm hard powder was further studied by biochem ical analysis,cytological observation and genetic verification.Starch chain length distribution analysis,molecular weight analysis and particle size analysis showed that the Su2 mutation le d to a decrease in amylopectin content,an increase in amylose content,changes in chain lengt h distribution and molecular weight distribution,and an increase in amylopectin A chain cont ent and B chain content reduce.Cytological observations and genetic analysis indicated that S u2 was a key factor in maintaining amyloplast morphology.Su2 increased the contact area wit h the protein body and the surrounding cytoplasmic matrix through the self-cleavage of the en dosperm amyloplast,which further supported and improved the theoretical model of the close fusion of the protein body and the amyloplast to form a hard endosperm.This study further improved the regulatory network of hard endosperm modification,pro vided a new theoretical basis for improving maize endosperm texture,and had both theoretica l significance and practical application value.