Strigolactones regulate shoot elongation by mediating gibberellin metabolism and signaling in rice (Oryza sativa L.).

Strigolactones (SLs) are plant hormones that regulate diverse physiological processes including shoot elongation. However, little is known about the regulatory mechanism of SLs in rice shoot elongation. Our results demonstrate that defects in SL biosynthesis or signaling led to dwarfism, and the dwarf statures of SL-deficient mutant (d17) and SL-insensitive mutant (d14) were restored to wild-type (WT) by gibberellin (GA) treatment, indicating that their dwarfism was associated with decreased GA content or weakened GA sensitivity. Our results indicate that the bioactive GA₁ contents in d17 and d14 were lower than those in WT, due to the downregulated transcription of GA biosynthesis genes and upregulated transcription of GA inactivation genes. Moreover, d17 and d14 exhibited weakened GA-responsive sensitivity compared with WT. Although the transcription levels of cell division- and cell elongation-related genes were upregulated by GA₃ treatment, the increase in transcription of d17 and d14 was lower than that in WT. These results suggest that SL is required for rice shoot elongation by mediating GA metabolism and signaling. Therefore, a deficiency in SL biosynthesis or signaling leads to decreased GA content and weakened GA response, which in turn reduces shoot length by downregulating transcription levels of cell division- and cell elongation-related genes.