Bimodular auxin response controls organogenesis in Arabidopsis

Abstract

Like animals, the mature plant body develops via successive sets of instructions that determine cell fate, patterning, and organogenesis. In the coordination of various developmental programs, several plant hormones play decisive roles, among which auxin is the best-documented hormonal signal. Despite the broad range of processes influenced by auxin, how such a single signaling molecule can be translated into a multitude of distinct responses remains unclear. In Arabidopsis thaliana , lateral root development is a classic example of a developmental process that is controlled by auxin at multiple stages. Therefore, we used lateral root formation as a model system to gain insight into the multifunctionality of auxin. We were able to demonstrate the complementary and sequential action of two discrete auxin response modules, the previously described SOLITARY ROOT/INDOLE-3-ACETIC ACID (IAA)14-AUXIN REPONSE FACTOR (ARF)7-ARF19–dependent lateral root initiation module and the successive BODENLOS/IAA12-MONOPTEROS/ARF5–dependent module, both of which are required for proper organogenesis. The genetic framework in which two successive auxin response modules control early steps of a developmental process adds an extra dimension to the complexity of auxin’s action.

Systems approaches map regulatory networks downstream of the auxin receptor AFB3 in the nitrate response ofArabidopsis thalianaroots

“…The IAA14(SLR)-ARF7-ARF19 module operates in the zone above the basal meristem and regulates the coordinated nuclear migration and posterior asymmetric cell division of the founder cells for lateral root initiation (36)(37)(38). IAA12(BDL)-ARF5(MP) also activates lateral root formation, acting after the IAA14(SLR)-ARF7-ARF19 module (39).…”

Root system architecture: insights fromArabidopsisand cereal crops

“…In turn, these genes direct the initial asymmetric pericycle cell divisions during lateral root formation [56]. Another factor required for correct cell patterning downstream of the SLR/IAA14-ARF7-ARF19 auxin response module is the BODENLOS (BDL)/IAA12-MONOPTEROS (MP)/ARF5-dependent module, which has both lateral-root-promoting and -inhibitory mechanisms [57]. The ARF protein MP was recently demonstrated to control both its own expression and the expression of its repressor, the AUX/IAA protein BDL, subject to a threshold level of auxin, suggesting that the ARF-AUX/IAA auxin response may be self-regulating [58].…”

Context, Specificity, and Self-Organization in Auxin Response

“…For example, for some time it has been known that a regulatory module consisting of the Aux/IAA SOLITARY ROOT (SLR/IAA14) and the ARFs NPH4/ARF7 and ARF19 is required for lateral root initiation and organogenesis (Fukaki et al 2002;Vanneste et al 2005). More recently a second module involving the Aux/IAA BODENLOS (BDL)/IAA12 and the ARF MP/ARF5 has been shown to act after SLR-ARF7/19 and indeed the over-expression of MP was able to suppress the lateral rootless phenotype of slr (De Smet et al 2010b). Although it is not clear whether the induction of this BDL/MP module is directly dependent on ARF7/19 regulation, BDL is certainly an auxin-inducible gene and there is evidence that MP expression is also moderately induced by auxin treatment (Abel et al 1995;Wenzel et al 2007).…”