The SHORT-ROOT Gene Controls Radial Patterning of the Arabidopsis Root through Radial Signaling

Abstract

Asymmetric cell divisions play an important role in the establishment and propagation of the cellular pattern of plant tissues. The SHORT-ROOT (SHR) gene is required for the asymmetric cell division responsible for formation of ground tissue (endodermis and cortex) as well as specification of endodermis in the Arabidopsis root. We show that SHR encodes a putative transcription factor with homology to SCARECROW (SCR). From analyses of gene expression and cell identity in genetically stable and unstable alleles of shr, we conclude that SHR functions upstream of SCR and participates in a radial signaling pathway. Consistent with a regulatory role in radial patterning, ectopic expression of SHR results in supernumerary cell divisions and abnormal cell specification in the root meristem.

Large-scale analysis of the GRAS gene family in Arabidopsis thaliana

“…1a). Of 33 GRAS genes, only a third was genetically analyzed: GAI, RGA, RGL1, RGL2, RGL3, SCR, SHR, PAT1, SCL13, and SCL18/ LAS (Di Laurenzio et al 1996;Peng et al 1997;Silverstone et al 1998;Bolle et al 2000;Helariutta et al 2000;Dill and Sun 2001;Lee et al 2002;Wen and Chang 2002;Greb et al 2003;Tyler et al 2004;Torres-Galea et al 2006). Typically, GRAS proteins share signature motifs of VHIID flanked by two leucine heptad repeats (LHRI and LHRII), PFYRE and SAW (designated after the profound amino acid residues in the conserved regions) with rather variable N-terminal regions (Pysh et al 1999;Bolle 2004).…”

“…In particular, SCL33, which encodes a polypeptide with 1336 amino acid residues, is unique among GRAS members due to the presence of two sets of GRAS signature motifs separated by an intron (940 bp). SHR, SCL29, and SCL32 belong to the branch III, and only SHR has been analyzed in detail (Helariutta et al 2000;Nakajima et al 2001). The branch IV comprises so-called ''DELLA'' proteins: GAI, RGA, RGL1, RGL2, and RGL3, which are negative regulators of GA signaling (Peng et al 1997;Silverstone et al 1998;Dill and Sun 2001;Lee et al 2002;Wen and Chang 2002;Tyler et al 2004).…”

“…Of 28 bait clones, 20 (71.4%) clones were able to activate the marker genes without prey clones (autoactivation), suggesting that these 20 GRAS members could act as transcription activators in yeast (Supplementary Table S4). Intriguingly, 8 of 20 autoactivating bait clones were previously reported as transcription regulators (Peng et al 1997;Silverstone et al 1998;Helariutta et al 2000; Lee et al 2002;Wen and Chang 2002;Greb et al 2003;Tyler et al 2004;Torres-Galea et al 2006). Excluding these 20 autoactivating bait clones, we performed pair-wise Y2H assay.…”

“…According to the current genome annotation (version 7.0), a total of 33 GRAS genes are predicted in Arabidopsis thaliana (TAIR, http://www.arabidopsis.org). Of them, only 10 GRAS genes were analyzed in detail thus far: GAI, RGA, RGL1, RGL2, RGL3, SCR, SHR, PAT1, SCL13, and SCL18/LAS (Di Laurenzio et al 1996;Peng et al 1997;Silverstone et al 1998;Bolle et al 2000;Helariutta et al 2000;Dill and Sun 2001;Lee et al 2002;Wen and Chang 2002;Greb et al 2003;Tyler et al 2004;Torres-Galea et al 2006). These genes play a crucial role in diverse plant growth and development, ranging from GA signaling, root radial pattering, light signal transduction, and axillary shoot meristem formation.…”

An R2R3-type transcription factor gene AtMYB59 regulates root growth and cell cycle progression in Arabidopsis

“…Mutations of SHR and SCR result in shorter roots. SHR may specify endodermal cell fate, whereas SCR mediates the division of the cortex/endodermal initial daughter cell [33,34]. Another MYB coiled-coil transcription factor gene, APL, may be necessary for phloem cell formation [35].…”