OsSPL14 is involved in nitrogen-deficiency-induced root elongation in rice

Nitrogen (N) is an essential element for rice (Oryza sativa L.) growth. Rice responds to N-limiting conditions by changing root morphology. Strigolactones (SLs) and auxin modulate rice root elongation under N-deficient conditions. However, the interactions between SLs and auxin in the regulation of root elongation in response to N deficiency remain needing further study. Here, we analysed the function of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 14 (SPL14, a downstream transcription factor of strigolactone signaling) in regulating root elongation under low N (LN) supply. Compared with sufficient N (SN) condition, LN and SN+GR24 (SL analogue) reduced protein interaction between SLs signaling repressor DWARF 53 (D53) and SPL14. The expression of SPL14 was induced by LN supply. In contrasts to WT plants, knockdown of SPL14 resulted in less extensive changes in root length under LN condition. Overexpression of SPL14 under SN supply enhanced root length to the same extent as WT plants under LN condition, suggesting that SPL14 was induced by LN condition and led to changes in root elongation. The transcription of PIN-FORMED 2 and 10b (auxin efflux carriers) were negatively and positively regulated by SPL14, respectively. Under SN and LN conditions, similar root morphology was observed in overexpressing PIN10b and SPL14 lines, and opposite root phenotypes were recorded between pin2 mutants and SPL14-RNAi lines.These results indicated that PIN2 and PIN10b were involved in SPL14-induced root elongation under LN condition. Therefore, we presented that, LN inhibits D53 and SPL14 interaction, which releases SPL14 to modulate the transcription of PIN2 and PIN10b, resulting in root elongation in rice.