AT-HOOK MOTIF NUCLEAR LOCALISED PROTEIN 18 as a Novel Modulator of Root System Architecture

Abstract

The AT-HOOK MOTIF NUCLEAR LOCALIZED PROTEIN (AHL) gene family encodes embryophyte-specific nuclear proteins with DNA binding activity. They modulate gene expression and affect various developmental processes in plants. We identify AHL18 (At3G60870) as a developmental modulator of root system architecture and growth. AHL18 regulates the length of the proliferation domain and number of dividing cells in the root apical meristem and thereby, cell production. Both primary root growth and lateral root development respond according to AHL18 transcription level. The ahl18 knock-out plants show reduced root systems due to a shorter primary root and a lower number of lateral roots. This change results from a higher number of arrested and non-developing lateral root primordia (LRP) rather than from decreased initiation. Overexpression of AHL18 results in a more extensive root system, longer primary roots, and increased density of lateral root initiation events. Formation of lateral roots is affected during the initiation of LRP and later development. AHL18 regulate root apical meristem activity, lateral root initiation and emergence, which is in accord with localization of its expression.

A histone modification-based synthetic circuit to engineer temporal gene expression in Arabidopsis floral meristems

“…Although AG has about 2,000 known target genes, KNU is the only one regulated by the AG biotimer 23 . Other AG targets associated with flower development and with regulatory roles include STYLISH1 (STY1) for proper carpel development by regulating auxin biosynthesis, INDETERMINATE DOMAIN12 (IDD12) associated with gibberellic acid biosynthesis and response, the recently characterized modulator of root system architecture AT HOOK MOTIF NUCLEAR LOCALIZED PROTEIN (AHL18), and PLATZ10 (PZ10), a member of the novel transcription factor class of plant-specific zinc-dependent DNA-binding proteins [24][25][26][27] . How these genes are regulated by AG remains largely unknown.…”

“…Only two genes were upregulated, SHOOTMERISTEMLESS (STM) and ZINC FINGER PROTEIN 1 (ZP1) 47,48 , suggesting that most candidate biotimer genes remain transcriptionally repressed without functional AG by the persistence of H3K27me3 marks. Aside from AT4G16540 and AT3G11150 (encoding a heat shock protein, HEAT-SHOCK PROTEIN 20 (HSP20) and an oxygenase, respectively), the downregulated genes encoded either transcription factors or proteins associated with DNA-binding transcription factor activity [49][50][51] : the zinc-finger proteins KNU, IDD12, and STY1 13,24,52 ; the transcription factor PLATZ10; a homeodomain-like protein (encoded by AT1G14600); and the AT h o o k d o m a i n -containing protein AHL18 26,[52][53][54] . Gene Ontology (GO) term enrichment analysis of these ten putative biotimer-regulated genes 55 revealed that the top ten GO terms are mainly associated with transcription, RNA biosynthesis and metabolism within the category of cellular processes, and various cellular biosynthetic processes (Fig.…”

“…The regulation of IDD12 via biotimer may therefore play an important role in the establishment and propagation of asymmetric cell divisions, and thus cellular patterns, in FMs. AHL18 is a regulator of lateral root development 26 . AHL family members have been implicated in the initiation of leaf senescence, hypocotyl elongation, phytohormone biosynthesis, and flowering time regulation [68][69][70][71][72][73][74][75] .…”