Lateral root emergence in Arabidopsis is dependent on transcription factor LBD29 regulating auxin influx carrier LAX3

Abstract

Lateral root primordia (LRP) originate from pericycle stem cells located deep within parental root tissues. LRP emerge through overlying root tissues by inducing auxin-dependent cell separation and hydraulic changes in adjacent cells. The auxin-inducible auxin influx carrier LAX3 plays a key role concentrating this signal in cells overlying LRP. Delimiting LAX3 expression to two adjacent cell files overlying new LRP is crucial to ensure that auxin-regulated cell separation occurs solely along their shared walls. Multiscale modeling has predicted that this highly focused pattern of expression requires auxin to sequentially induce auxin efflux and influx carriers PIN3 and LAX3, respectively. Consistent with model predictions, we report that auxin-inducible LAX3 expression is regulated indirectly by AUXIN RESPONSE FACTOR 7 (ARF7). Yeast one-hybrid screens revealed that the LAX3 promoter is bound by the transcription factor LBD29, which is a direct target for regulation by ARF7. Disrupting auxin-inducible LBD29 expression or expressing an LBD29-SRDX transcriptional repressor phenocopied the lax3 mutant, resulting in delayed lateral root emergence. We conclude that sequential LBD29 and LAX3 induction by auxin is required to coordinate cell separation and organ emergence.

Control of Arabidopsis lateral root primordium boundaries by MYB36

“…Several mechanisms contribute to the growth of LRP including a defined auxin transport (Marhavy et al, 2016). LRP emergence through the outer root cell layers involves active crosstalk with overlying layers such as the endodermis and cortex (Swarup et al, 2008;Marhavy et al, 2013;Porco et al, 2016). In addition, reactive oxygen species (ROS) have recently been implicated in lateral root development, although the complex gene network is still largely unknown (Manzano et al, 2014;Reyt et al, 2015;Orman-Ligeza et al, 2016).…”

Lateral root initiation requires the sequential induction of transcription factors LBD16 and PUCHI in Arabidopsis thaliana

“…LBD16 and its related LBD family members (LBD17, LBD18, LBD29 and LBD33) are expressed in the root under the regulation of the auxin signaling pathway and function redundantly in the multiple steps of LR development events (Okushima et al ., ; Lee et al ., , ; Berckmans et al ., ; Goh et al ., ; Porco et al ., ). Compared with other LBD family members, our data suggest that LBD16 and its targets function in close association with the LR initiation processes.…”

LBD18 uses a dual mode of a positive feedback loop to regulate ARF expression and transcriptional activity in Arabidopsis

“…LAX3 affects the auxin influx of outer endodermis and cortex cells, and induces the expression of cell‐wall‐remodeling enzymes, promoting lateral root emergence by weakening the walls of overlaying cells and thus separating the overlaying cells (Swarup et al ., ). The expression of LAX3 is auxin inducible and dependent upon ARF7‐LBD29, and thus this regulatory arrangement creates a positive feedback loop (Swarup et al ., ; Porco et al ., ). The gene regulatory network that controls lateral root formation in Arabidopsis has been inferred using a time‐delay correlation algorithm (Lavenus et al ., ).…”