Gene ontology (GO) enrichment analysis revealed
transcription factors were over-represented amongst DEGs
in most pairwise comparisons (Table S1). This category
contained 61 differentially expressed homeobox genes,
some of which have known roles in meristem and organ
initiation. For example, WOX13 is dynamically expressed
during RAM/LRP initiation, and showed decreased expression on 2iP. Conversely, ARABIDOPSIS THALIANA
HOMEOBOX 1 (ATH1) and PENNYWISE (PNY) interact with
SHOOT MERISTEMLESS 1 (STM1) in the SAM, and their
expression was increased.
Comparison with callus-based regeneration reveals an
overlap with DEGs identified in LRP? SM conversion
To identify potential key regulators of shoot regeneration
common to different in vitro systems, we compared
targets identified in studies of shoot organogenesis from
callus with LRP ? SM conversion. Che et al. (2006)
analysed transcriptome changes during root or shoot
organogenesis from callus, and described the ‘top-20’
DEGs with increased/decreased expression during callus
induction, or subsequent shoot or root induction. Of the top-20 DEGs identified during presumed commitment to
shoot organogenesis, 11 and 12 of the genes with
increased and decreased expression, respectively, also
appeared amongst the DEGs identified in our study, with
similar patterns of expression (Table S6).
We then surveyed genes previously identified as affecting shoot organogenesis for differential expression during
LRP ? SM conversion (Table S7). One of these, HLS1/
COP3, is a negative regulator of callus-based shoot regeneration (Chatfield and Raizada, 2008), and exhibits >14-fold
decrease in expression levels on 2iP in our study (Table
S7). Interestingly, RSM1 overexpression phenocopies loss
of HLS1 function (Hamaguchi et al., 2008), and RSM1
expression was increased more than eightfold on 2iP.