LBD16 and LBD18 acting downstream of ARF7 and ARF19 are involved in adventitious root formation in Arabidopsis

Han Woo Lee,Shashank K Pandey,Yoona Park,Jungmook Kim,Chuloh Cho,Min-Jung Kim

doi:10.1186/s12870-019-1659-4

Abstract

BackgroundAdventitious root (AR) formation is a complex genetic trait, which is controlled by various endogenous and environmental cues. Auxin is known to play a central role in AR formation; however, the mechanisms underlying this role are not well understood.ResultsIn this study, we showed that a previously identified auxin signaling module, AUXIN RESPONSE FACTOR(ARF)7/ARF19-LATERAL ORGAN BOUNDARIES DOMAIN(LBD)16/LBD18 via AUXIN1(AUX1)/LIKE-AUXIN3 (LAX3) auxin influx carriers, which plays important roles in lateral root formation, is involved in AR formation in Arabidopsis. In aux1, lax3, arf7, arf19, lbd16 and lbd18 single mutants, we observed reduced numbers of ARs than in the wild type. Double and triple mutants exhibited an additional decrease in AR numbers compared with the corresponding single or double mutants, respectively, and the aux1 lax3 lbd16 lbd18 quadruple mutant was devoid of ARs. Expression of LBD16 or LBD18 under their own promoters in lbd16 or lbd18 mutants rescued the reduced number of ARs to wild-type levels. LBD16 or LBD18 fused to a dominant SRDX repressor suppressed promoter activity of the cell cycle gene, Cyclin-Dependent Kinase(CDK)A1;1, to some extent. Expression of LBD16 or LBD18 was significantly reduced in arf7 and arf19 mutants during AR formation in a light-dependent manner, but not in arf6 and arf8. GUS expression analysis of promoter-GUS reporter transgenic lines revealed overlapping expression patterns for LBD16, LBD18, ARF7, ARF19 and LAX3 in AR primordia.ConclusionThese results suggest that the ARF7/ARF19-LBD16/LBD18 transcriptional module via the AUX1/LAX3 auxin influx carriers plays an important role in AR formation in Arabidopsis.

Highlights

Adventitious root (AR) formation is a complex genetic trait, which is controlled by various endogenous and environmental cues
We show that the AUX1/LAX3-ARF7/ARF19-LBD16/ LBD18 signaling module is important for AR formation in Arabidopsis, providing evidence of a common regulatory mechanism being utilized for lateral roots (LRs) and AR formation during auxin signaling
In ProARF7:GUS, ProARF19:GUS and ProLAX3:GUS seedlings, GUS expression was detected in both the hypocotyl stele tissue and AR primordium after transferring 3-d-old dark-grown seedlings to the light for 72 h (Fig. 1g–o). These overlapping and distinctive GUS expression patterns in the hypocotyl stele tissue and AR primordium of the GUS reporter transgenic lines indicated that LBD16 and LBD18 may play an overlapping role in early AR primordium development and LBD18 may play a distinctive role in the AR primordium in later developmental stages downstream of ARF7/ARF19-LAX3 during AR development

Summary

Introduction

Adventitious root (AR) formation is a complex genetic trait, which is controlled by various endogenous and environmental cues. Dicotyledonous plants, such as Arabidopsis thaliana, have a primary root that branches to form lateral roots (LRs). In both monocot and dicotyledonous plants, the primary root can develop adventitious roots (ARs) that arise naturally from the aerial organs as an adaptive response to environmental changes, such as flooding and dark-light transitions, or artificially by. Plant root development is regulated by establishing auxin maxima at the primordium tip through auxin transport [10,11,12,13]. SlCYP1 changes the abundance of PIN efflux carriers at the plasma membrane to modulate polar auxin transport during AR initiation [26,27,28,29]

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