Fertilization controls tiller numbers via transcriptional regulation of a MAX1-like gene in rice cultivation. Oryza sativa cultivar:koshihikari

Fertilization controls various aspects of cereal plant growth such as tiller number, leaf size, and panicle size; however, the molecular mechanisms underlying this control remain elusive. To achieve sustainable agriculture, reduced global chemical fertilizer use is required. In this study, based on field transcriptome data from leaf samples collected during rice cultivation, we examined Os1900, a gene orthologous to Arabidopsis thaliana MAX1, which is involved in strigolactone biosynthesis. Elaborate genetic and biochemical analyses using mutants induced by CRISPR/Cas9 revealed that both Os1900 and another MAX1-like gene, Os5100, together play a critical role in controlling carlactone conversion into carlactonoic acid in strigolactone biosynthesis and tiller numbers in rice. Unexpectedly, other MAX1-like genes were previously identified as related quantitative trait loci. Detailed analysis of a series of deletion mutations in the Os1900 promoter revealed that fertilization controls tiller number in rice through transcriptional regulation of Os1900 and that multiple promoter mutations alone, without Os5100 mutations, function as novel alleles increasing and maintaining tiller numbers, even under minor fertilizer conditions whereas a single defective os1900 mutation produced no change in tiller number. Thus, such Os1900 promoter mutations may be applied in breeding programs to attain sustainable rice production.