RopGEF7Regulates PLETHORA-Dependent Maintenance of the Root Stem Cell Niche inArabidopsis     

Abstract

The root stem cell niche defines the area that specifies and maintains the stem cells and is essential for the maintenance of root growth. Here, we characterize and examine the functional role of a quiescent center (QC)-expressed RAC/ROP GTPase activator, RopGEF7, in Arabidopsis thaliana. We show that RopGEF7 interacts with At RAC1 and overexpression of a C-terminally truncated constitutively active RopGEF7 (RopGEF7DC) activates RAC/ROP GTPases. Knockdown of RopGEF7 by RNA interference causes defects in embryo patterning and maintenance of the QC and leads to postembryonic loss of root stem cell population. Gene expression studies indicate that RopGEF7 is required for root meristem maintenance as it regulates the expression of PLETHORA1 (PLT1) and PLT2, which are key transcription factors that mediate the patterning of the root stem cell niche. Genetic analyses show that RopGEF7 interacts with PLT genes to regulate QC maintenance. Moreover, RopGEF7 is induced transcriptionally by auxin while its function is required for the expression of the auxin efflux protein PIN1 and maintenance of normal auxin maxima in embryos and seedling roots. These results suggest that RopGEF7 may integrate auxin-derived positional information in a feed-forward mechanism, regulating PLT transcription factors and thereby controlling the maintenance of root stem cell niches.

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

“…There are only two studies that show homeotic transformation of cotyledons into roots: one by the expression of either a dominant-negative version of Rab5 GTPase Ara7 or RNA interference of a Rab5-GEF gene, AtVps9a (Dhonukshe et al, 2008); and one by expressing constitutively active RopGEF7 (Chen et al, 2011). In the former case, auxin response maxima at the tips of developing cotyledons were larger in transgenic plants than those in wild type (Dhonukshe et al, 2008).…”

ROP GTPases Structure-Function and Signaling Pathways

“…Two reports indicated that ROPGEF1 and ROPGEF7 have specific functions during embryo development. ROPGEF7 RNA interference (RNAi) plants displayed compromised stem cell maintenance in embryo and roots (Chen et al, 2011). The ropgef1 mutants are characterized by defective embryo development and embryo auxin distribution and a mild gravitropic response phenotype , suggesting that the ROPGEF1 function in embryos is unique.…”

Signals fly when kinases meet Rho-of-plants (ROP) small G-proteins

“…It was hypothesized that the regulation of secondary cell wall patterning might rely on receptor-like kinases acting upstream of the RopGEF-ROP module [30]. The Arabidopsis RopGEF7 interacting with ROP3 is required for polar auxin transport and meristem maintenance in the root [25]. Considering their overlapping expression patterns and direct interaction in a yeast two-hybrid assay, the FERONIA receptor kinase has been proposed as a potential upstream regulator of RopGEF7 [18,24].…”

“…The identification of rop or ropgef mutants with clavata1 mutant-like phenotypes (enlarged shoot and flower meristems, additional lateral organs, and/or disrupted organ placements) could provide genetic evidence for the role of the potential CLAVATA1-RopGEF-ROP complex in shoot meristem maintenance. Null mutations of these genes might cause embryo lethality, similarly to the ropgef7 mutation that affects the root meristem development negatively and results in non-viable embryos [25]. The silencing of rop and/or ropgef genes would be an alternative approach that could result in viable transgenic plants with decreased RNA levels, allowing the investigation of postembryonic phenotypes [25].…”

“…Null mutations of these genes might cause embryo lethality, similarly to the ropgef7 mutation that affects the root meristem development negatively and results in non-viable embryos [25]. The silencing of rop and/or ropgef genes would be an alternative approach that could result in viable transgenic plants with decreased RNA levels, allowing the investigation of postembryonic phenotypes [25].…”