OsSPL14/17 are required for phosphate-deficiency-inhibited tiller bud outgrowth by repression of PIN2 in rice

Phosphorus (P) is an essential nutrient for food crops. P-deficiency inhibits tiller development of rice; thus, an understanding of the P-modulated tiller development mechanism is crucial for grain yield. Auxin and strigolactones (SLs) have been implicated as regulators of tiller formation in rice. However, the relationships between the two are unclear. We found that low-P (LP) inhibited rice tiller formation and tiller bud elongation, with higher levels of SLs. In contrast to wild-type (WT) plants, the number of tillers was greater in d10 (SL biosynthesis mutant), d14, and d53 (SL-responsive mutants) under LP conditions, demonstrating that D53 participates in LP- mediated inhibition of rice tiller formation. The strong interaction between D53 and SPL14/17 inhibited their transcriptional activities under normal P (NP) conditions, and mutation of SPL14/17 eliminated their inhibitory effects on tiller formation under LP conditions. SPL14/17 inhibited transcriptional from the PIN2 promoter, and overexpression of PIN2 induced tiller development under LP conditions. Therefore, binding of D53 to SPL14/17 represses their transcriptional inhibition, reversing SPL14/17-inhibited PIN2 transcription and promoting tiller development under NP conditions. Proteasomal degradation of D53 releases SPL14/17, thus repressing PIN2 transcription and preventing induction of tillering under LP conditions.