▎ 摘　　要

NOVELTY - OsCESA9 mutant, is new. The OsCESA9 mutant is that the 396th amino acid S of OsCESA9 protein is mutated to L. The mutant protein having fully defined sequence of 1055 amino acids (SEQ ID NO. 2) as given in the specification, and encoding the mutein having fully defined sequence of 3168 nucleotide (SEQ ID NO. 1) as given in the specification. USE - The OsCESA9 mutant is useful for improving polymerization degree of rice stem cellulose (claimed), and preparing graphene. ADVANTAGE - The OsCESA9 mutant improves rice stalk cellulose, and quality of graphene. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: 1 recombinant vector constructed based on CRISPR/Cas9 gene editing, comprising gRNA spacer sequence; 2 host cell, comprising the recombinant vector; 3 use of OsCESA9 mutant, gRNA spacer sequence, recombinant vector or host cell are in improving the degree of polymerization of rice stem cellulose, and reducing the degree of polymerization of cellulose in plant stems; 4 construction method of mutant rice, comprising introducing recombinant vector into wild-type rice in Japan to obtain mutant plants with reduced cellulose polymerization degree of stems; 5 use of OsCESA9 mutant in preparing graphene, comprising using the construction method for constructing a rice mutant plant to obtain the stalk cellulose of the rice mutant plant, mixing and reacting the stalk cellulose and ferrous chloride tetrahydrate to obtain graphene; anf 6 construction method of the described OsCESA9 mutant, comprising (i) using the gRNAspacer sequence as the target site, synthesizing the double-stranded spacer sequence with the enzyme cleavage site, (ii) transferring the sequence into a plasmid by enzymatic ligation for constructing a recombinant vector, transferring recombinant vector into competent bacteria, screening positive colonies and extracting plasmids, transferring the extracted plasmid into Agrobacterium, and screening to obtain positive colony of Agrobacterium, (iii) infecting plants with the Agrobacterium-positive bacterial colonies to obtain tissue culture seedlings through tissue culture, and (iv) extracting DNA in the tissue culture seedlings, screening the transgenic positive seedlings, then amplifying a gene fragment with a length of 1000bp upstream and downstream of the target site, sequencing and screening to obtain OsCESA9 mutant.