OsPIN2 is involved in OsSPL14/17-inhibited tiller bud outgrowth in response to phosphate deficiency 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 strigo-lactones (SLs) have been implicated as regulators of tiller formation in rice. However, the relationships between the two in P-modulated tiller development are unclear. Here we found that low-P (LP) inhibited rice tiller for-mation and tiller bud elongation, with higher levels of SLs. The strong interaction between D53 (SL signaling repressor) and SPL14 and 17 (SPL14/17) inhibited their transcriptional activities under normal P (NP) condition, and mutations of SPL14/17 eliminated their inhibitory effects on tiller formation under LP condition, showing SPL14/17 act downstream of SLs signaling to inhibit tiller formation under P-deficiency in rice. Meanwhile, the expression levels of PIN2 were down-regulated under conditions of either LP and NP treated with GR24 when compared with NP condition, demonstrating SLs negative regulation of PIN2 transcription under LP condition. Further study showed that SPL14/17 inhibited the transcription expression of PIN2, and the knockout of PIN2 reduced tiller development by LP condition. Therefore, we presented that, under NP condition, bindings of D53 to SPL14/17 repress their transcriptional inhibition, reversing SPL14/17-inhibited PIN2 transcription and pro-moting tiller development. Proteasomal degradation of D53 releases SPL14/17, thus repressing PIN2 tran-scription and preventing production of tillering under LP condition.