Disruption of the cytochrome CYP711A5 gene reveals MAX1 redundancy in rice strigolactone biosynthesis

Strigolactones (SLs) inhibit shoot branching/tillering and are secreted by plant roots as a signal to attract symbiotic mycorrhizal fungi in the rhizosphere, particularly under phosphate starvation. However, SLs are also hijacked by root parasitic weeds as inducer for the germination of their seeds. There are around 35 natural SLs divided, based on their structures, into canonical and non-canonical SLs. Cytochrome P450 enzymes of the 711 clade, such as MORE AXILLARY GROWTH1 (MAX1) in Arabidopsis, are a major driver of SL structural diversity. Monocots, such as rice, contain several MAX1 homologs that participate in SL biosynthesis. To investigate the function of OsMAX1-1900 in planta, we generated CRISPR/Cas9 mutants disrupted in the corresponding gene. Characterizing of the generated mutants at metabolite and phenotype level suggests that OsMAX1-1900 loss-of-function does neither affect the SL pattern nor rice architecture, indicating functional redundancy among rice MAX1 homologs.