At-Hook Motif Nuclear Localised Protein 18 as a Novel Modulator of Root System Architecture.

The Localized () gene family encodes embryophyte-specific nuclear proteins with DNA binding activity. They modulate gene expression and affect various developmental processes in plants. We identify (At3G60870) as a developmental modulator of root system architecture and growth. is involved in regulation of 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 transcription level. The 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 a decreased LRP initiation. The over-expression of results in a more extensive root system, longer primary roots, and increased density of lateral root initiation events. is thus involved in the formation of lateral roots at both LRP initiation and their later development. We conclude that participates in modulation of root system architecture through regulation of root apical meristem activity, lateral root initiation and emergence; these correspond well with expression pattern of .