Salicylic acid represses primary root growth through the Glucose-Target of Rapamycin-E2Fa pathway in Arabidopsis

In addition to their role as energy sources, sugars function as signaling molecules, modulating gene expression. Plants perceive nutrient availability and translate this information into cellular signals, to trigger various developmental responses, including primary root growth. In particular, glucose stimulates root development by activating the root meristem. Recent studies have documented the role of the defense hormone, salicylic acid (SA) as a negative regulator of root growth and developmental processes. Here, we characterized the modulation of primary root growth by the cross-talk of glucose and SA. Our results indicate that auxin is a critical mediator of SA-induced root growth inhibition. Attenuation of auxin signaling or transport pathways alters the inhibitory effect of SA on root growth. Moreover, we provide evidence for the involvement of the role of Target of Rapamycin (TOR) signaling in SA-induced root growth repression. Furthermore, SA negatively regulates the expression of E2Fa, a key transcription factor required for cell cycle progression and root growth and development. Our findings elucidate mechanism(s) whereby SA, through the interconnected glucose, auxin and TOR signaling pathways, inhibits primary root growth.