Strigolactone and karrikin receptors regulate phytohormone biosynthetic and catabolic processes.

Karrikin plays a more critical role in affecting the homeostasis of ABA and cytokinins, while strigolactones play a more critical role in influencing the homeostasis of jasmonic acid and gibberellins. Strigolactones (SLs) and karrikins (KARs) regulate plant growth and development through their crosstalk, and through the crosstalk between them and other phytohormones, such as abscisic acid (ABA) and auxin. However, how SL and KAR signaling pathways influence the levels of other phytohormones is still unknown. Here, we performed a comparative transcriptome analysis of the Arabidopsis thaliana double mutant dwarf14 karrikin-insensitive 2 (d14 kai2), deficient in SL and KAR perception, and the wild-type (WT) using their rosette leaves. Ten gene ontology terms related to phytohormones were enriched with differentially expressed genes derived from the 'd14 kai2 vs WT' comparison. Our data revealed that the levels of auxin, ABA and salicylic acid (SA) were higher in d14 and kai2 single and d14 kai2 mutant plants than in WT, which was consistent with the results of previous investigations. In contrast, the levels of cytokinins (CKs) were found to be lower in all single and double mutants than in WT. The levels of active gibberellins were lower in d14 and d14 kai2 mutants than in WT, while they were comparable in kai2 and WT plants. Similarly, the levels of jasmonic acid (JA) were lower in d14 and d14 kai2 plants, but higher in kai2 plants than in WT. Both transcriptome and qRT-PCR analyses indicated that SL and KAR signaling pathways affect the levels of auxin, SA, CKs, gibberellin 4 (GA) and ABA by influencing the expression of their biosynthetic (in case of auxin, SA, GA and CKs) and catabolic (in case of ABA) genes. Collectively, our data demonstrated that KAI2 plays a more critical role in the homeostasis of ABA and CKs, while D14 plays a more critical role in the homeostasis of JA and gibberellins. Findings of this study indicate a complex and broad crosstalk among various phytohormones in plants, which can be considered for future exogenous applications and hormone engineering.