Identification Of A Novel Mutant Allele, Fzp-15, Involved In Panicle Branch Pattern Of Rice (Oryza Sativa)

FRIZZY PANICLE (FZP) is involved in the development of panicle branching in rice. Herein, a novel mutant fzp-15, demonstrating the sequential rounds of branching and severe defects in SM (spikelet meristem) formation, was identified. Map-based cloning revealed that the abnormal panicle architecture of fzp-15 resulted from an amino acid substitution (Glu (E) to Ala (A)) in the N-terminal ERF domain of rice FZP protein. To generate new advantageous FZP alleles increasing grain numbers, CRISPR/Cas9 multiplex editing system was used to target the 5' untranslation region (UTR) of FZP in 'Nipponbare' (NIP). The 85-bp (-156 to -72 bp) or 149-bp (-157 to -9 bp) deletion in the upstream region of FZP can significantly increase grain numbers without a decrease in grain size, while the 38-bp deletion (-44 to -7 bp) in the upstream region of FZP has little effect in changing grain numbers. These results indicated that the 113-bp fragment (-157 to -45 bp) upstream of FZP is important to its function and deletion of this region can be used to increase grain numbers in rice.