Molecular analysis of theLATERAL SUPPRESSORgene inArabidopsisreveals a conserved control mechanism for axillary meristem formation

Abstract

In seed plants, shoot branching is initiated by the formation of new meristems in the axils of leaves, which subsequently develop into new axes of growth. This study describes the genetic control of axillary meristem formation by the LATERAL SUPPRESSOR (LAS) gene in Arabidopsis thaliana. las mutants show a novel phenotype that is characterized by the inability to form lateral shoots during vegetative development. The analysis shows that axillary meristem formation is differently regulated during different phases of development. During reproductive development, axillary meristems initiate in close proximity to the shoot apical meristem and do not require LAS function. In contrast, during the vegetative phase, axillary meristems initiate at a distance to the SAM and require LAS function. This control mechanism is conserved between the distantly related species tomato and Arabidopsis. Monitoring the patterns of LAS and SHOOT MERISTEMLESS transcript accumulation allowed us to identify early steps in the development of leaf axil identity, which seem to be a prerequisite for axillary meristem initiation. Other regulators of shoot branching, like REVOLUTA and AUXIN RESISTANT 1, act downstream of LAS. The results are discussed in the context of the "detached meristem" and the "de novo formation" concepts of axillary meristem formation.

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).…”

“…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.…”

Using Arabidopsis to Study Shoot Branching in Biomass Willow

“…MAX SL biosynthesis genes but not by the SL signaling gene SxMAX2. A, The branching assay was as described by Greb et al (2003). Branch numbers were determined in 10 independent transgenic lines per Salix spp.…”

“…Testing allelic variation in SxMAX4 alleles through the rescue of branching in max4. The branching assay was as described by Greb et al (2003). Branch numbers were determined for each of the three Salix spp.…”