ARF7 and ARF19 Regulate Lateral Root Formation via Direct Activation ofLBD/ASLGenes inArabidopsis

Abstract

Lateral root formation in Arabidopsis thaliana is regulated by two related AUXIN RESPONSE FACTORs, ARF7 and ARF19, which are transcriptional activators of early auxin response genes. The arf7 arf19 double knockout mutant is severely impaired in lateral root formation. Target-gene analysis in arf7 arf19 transgenic plants harboring inducible forms of ARF7 and ARF19 revealed that ARF7 and ARF19 directly regulate the auxin-mediated transcription of LATERAL ORGAN BOUNDARIES-DOMAIN16/ASYMMETRIC LEAVES2-LIKE18 (LBD16/ASL18) and/or LBD29/ASL16 in roots. Overexpression of LBD16/ASL18 and LBD29/ASL16 induces lateral root formation in the absence of ARF7 and ARF19. These LBD/ASL proteins are localized in the nucleus, and dominant repression of LBD16/ASL18 activity inhibits lateral root formation and auxin-mediated gene expression, strongly suggesting that these LBD/ASLs function downstream of ARF7-and ARF19-dependent auxin signaling in lateral root formation. Our results reveal that ARFs regulate lateral root formation via direct activation of LBD/ASLs in Arabidopsis.

LATERAL ORGAN BOUNDARIES DOMAIN transcription factors direct callus formation in Arabidopsis regeneration

“…To investigate the temporal and spatial expression of LBD genes during callus induction, we chose LBD16 and LBD18 as the representatives and carefully examined their expression patterns during callus induction using ProLBD16:GUS and ProLBD18:EGFP:GUS transgenic seedlings. Consistent with previous observations [27,28,35], LBD16 was only expressed in LRP, root stele nearby LRP and emerged lateral roots ( Figure 2A). However, after seedlings were incubated on CIM for 12 h, GUS staining expanded to the stele of elongation zone in primary roots ( Figure 2B), and subsequently to leaves and the vascular tissues of both roots and hypocotyls after 24 h ( Figure 2C).…”

“…Of the 43 LBD members in the Arabidopsis genome, the expressions of LBD16, LBD17, LBD18 and LBD29 are all inducible by auxin [28,36], a phytohormone required for callus induction in in vitro plant regeneration [15]. More importantly, LBD16, LBD29 and LBD18 have been shown to regulate lateral root formation, a pathway that callus formation may follow [12,14,27,28].…”

“…expressed in young lateral roots and LBD29 in lateral root primordia, while LBD18 was more ubiquitously detected in most organs [19,28,34]. To investigate the temporal and spatial expression of LBD genes during callus induction, we chose LBD16 and LBD18 as the representatives and carefully examined their expression patterns during callus induction using ProLBD16:GUS and ProLBD18:EGFP:GUS transgenic seedlings.…”

“…Importantly, LBD genes are critical for root development in both dicots and monocots. Arabidopsis LBD16, LBD29 and LBD18 have been found to be direct or indirect targets of AUXIN RESPONSE FACTORs (ARFs), ARF7 and ARF19, to synergistically regulate lateral root formation [27,28], demonstrating that LBD genes are directly involved in the auxin signal cascades in lateral root patterning. Rice CROWN ROOTLESS1 and maize ROOTLESS CON-CERNING CROWN AND SEMINAL ROOTS, two close homologues of Arabidopsis LBD29, regulate the formation of monocot-specific crown roots [29][30][31].…”

Combinatorial interactions between LBD10 and LBD27 are essential for male gametophyte development in Arabidopsis

“…9 In Arabidopsis, LBD6 functions in the establishment of adaxial-abaxial polarity, 10 LBD30 is involved in embryogenesis, 11 and LBD16, LBD18, LBD29 and LBD33 control lateral root development. [12][13][14] As the Arabidopsis eFP browser showed that LBD10 expression was specifically and strongly increased during pollen development, we conducted functional Keywords: asymmetric cell division, lateral organ boundaries domain, LBD10, LBD27, plant development, pollen development, transcription factor Abbreviations: ASL, asymmetric leaves 2-like; LBD, lateral organ boundaries domain; SCP, sidecar pollen.…”