Strigolactones Interact With Nitric Oxide in Regulating Root System Architecture ofArabidopsis thaliana

Both nitric oxide (NO) and strigolactone (SL) are growth regulating signal components in plants; however, regarding their possible interplay our knowledge is limited. Therefore, this study aims to provide new evidence for the signal interplay between NO and SL in the formation of root system architecture using complementary pharmacological and molecular biological approaches in the modelArabidopsis thalianagrown under stress-free conditions. Deficiency of SL synthesis or signaling (max1-1andmax2-1) resulted in elevated NO andS-nitrosothiol (SNO) levels due to decreasedS-nitrosoglutathione (GSNO) reductase (GSNOR) protein abundance and activity indicating that there is a signal interaction between SLs and GSNOR-regulated levels of NO/SNO. This was further supported by the down-regulation of SL biosynthetic genes (CCD7, CCD8andMAX1) in GSNOR-deficientgsnor1-3. Based on the more pronounced sensitivity ofgsnor1-3to exogenous SL (rac-GR24, 2 mu M), we suspected that functional GSNOR is needed to control NO/SNO levels during SL-induced primary root (PR) elongation. Additionally, SLs may be involved in GSNO-regulated PR shortening as suggested by the relative insensitivity ofmax1-1andmax2-1mutants to exogenous GSNO (250 mu M). Collectively, our results indicate a connection between SL and GSNOR-regulated NO/SNO signals in roots ofA. thalianagrown in stress-free environment. As this work usedmax2-1mutant andrac-GR24 exerting unspecific effects to both SL and karrikin signaling, it cannot be ruled out that karrikins are partly responsible for the observed effects, and this issue needs further clarification in the future.