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

• DOI: 10.1242/dev.136283
• Publication Date: 2016-08-31T02:03:49Z
• Authors: Silvana Porco; Antoine Larrieu; Yujuan Du; Allison Gaudinier; Tatsuaki Goh; Kamal Swarup; Ranjan Swarup; Britta Kuempers; Anthony Bishopp; Julien Lavenus; Ilda Casimiro; Kristine Hill; Eva Benkova; Hidehiro Fukaki; Siobhan M. Brady; Ben Scheres; Benjamin Péret; Malcolm J. Bennett
• Keywords: 0301 basic medicine; lateral root emergence; root development; Arabidopsis; 580 Plants (Botany); racine laterale; Plant Roots; LBD29; 03 medical and health sciences; Gene Expression Regulation, Plant; lateral root emergence;LBD29;arabidopsis;root development;auxin; [SDV.BV]Life Sciences [q-bio]/Vegetal Biology; Auxin; développement racinaire; 580; Vegetal Biology; auxine; Indoleacetic Acids; Arabidopsis Proteins; Membrane Transport Proteins; Lateral root emergence; Root development; arabidopsis; auxin; Biologie végétale; Signal Transduction; Transcription Factors

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 critical to ensure auxin-regulated cell separation occurs solely along their shared walls. Multiscale modeling has predicted 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 LAX3 auxin inducible expression is regulated indirectly by the AUXIN RESPONSE FACTOR ARF7. Yeast-1-hybrid screens revealed 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.