06; Dello Ioio et al., 2007).
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
Figure 3. Distribution of differentially expressed genes (DEGs) during conversion of lateral root promordia (LRP) to shoot meristems (SMs) in a pairwise comparison of three different durations of cytokinin treatment (4.4 lM
2iP). ‘0 h’ corresponds to 24 h of LRP-induction using 10 lM 1-naphthaleneacetic acid (1-NAA). Overlap in DEGs between time points is high, suggesting substantial common transcriptional responses to auxin ? cytokinin
transfer.