Repression of Apical Homeobox Genes Is Required for Embryonic Root Development in Arabidopsis

Abstract

Development of seed plant embryos is polarized along the apical-basal axis. This polarization occurs in the absence of cell migration and culminates in the establishment of two distinct pluripotent cell populations: the shoot apical meristem (SAM) and root meristem (RM), which postembryonically give rise to the entire shoot and root systems of the plant. The acquisition of genetic pathways that delimit root from shoot during embryogenesis must have played a pivotal role during land plant evolution because roots evolved after shoots in ancestral vascular plants and may be shoot-derived organs. However, such pathways are very poorly understood. Here we show that RM establishment in the model plant Arabidopsis thaliana requires apical confinement of the Class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) proteins PHABULOSA (PHB) and PHAVOLUTA (PHV), which direct both SAM development and shoot lateral organ polarity. Failure to restrict PHB and PHV expression apically via a microRNA-dependent pathway prevents correct elaboration of the embryonic root development program and results in embryo lethality. As such, repression of a fundamental shoot development pathway is essential for correct root development. Additionally, our data suggest that a single patterning process, based on HD-ZIP III repression, mediates both apical-basal and radial polarity in the embryo and lateral organ polarity in the shoot.

Genome-wide profiling of sRNAs in the Verticillium dahliae-infected Arabidopsis roots

“…Among these genes, ARF10, NAC1, TAS3 and ARF6 are known to be involved in auxin signals transduction (Chandler 2016). PHV targeted by miR166 is functional in shoot and root apical meristems (Grigg et al 2009). Opposed to miRNAs induced by V592-infection, the expression of ARF10, NAC1, ARF6 and PHV was significantly reduced (Figure 4(b)) ( P -value < 0.05, t -test).…”

The pivotal role of small non-coding RNAs in the regulation of seed development

“…Repression of PHB and PHV is critical for patterning along the apical-basal axis. SE/miR165/6 activity is responsible for the functionally important change that occurs at the 32-cell embryo stage when organization of the root stem cell niche begins, and during which PHB expression at the embryo-proper becomes restricted to the apical part (Grigg et al 2009). While the se-1 allele seems to cause only a partial loss of function, the allele se-4 is embryonic lethal similarly to null dcl1 alleles, causing abnormal development visible at the heart embryo stage.…”

“…SERRATE (SE) is another protein found to participate in the miRNA biogenesis pathway that by acting together with HYL1 and DCL1, promotes accurate in vitro conversion of pri-miRNAs to miRNAs (Lobbes et al 2006;Yang et al 2006;Dong et al 2008). SE-mediated repression of HD-ZIP III genes is required to the correct patterning of the embryonic root by repressing players of the shoot developmental pathway (Grigg et al 2009). Repression of PHB and PHV is critical for patterning along the apical-basal axis.…”

Stable establishment of cotyledon identity during embryogenesis in Arabidopsis by ANGUSTIFOLIA3 and HANABA TARANU

“…For normal embryonic root development, HD-ZIP III genes must be repressed (Grigg et al, 2009). Similarly, repression of PLT at the apical region by TOPLESS (TPL) is necessary for normal shoot development (Long et al, 2002;Long et al, 2006;Smith and Long, 2010).…”