Our interest in AtSBT1.1 stems from our earlier studies of shoot regeneration in Arabidopsis (Lall et al., 2004) . We found that higher expression levels of the gene encoding AtSBT1.1 (At1g01900) correlated with the presence of the superior allele at the major QTL conditioning shoot regeneration in Arabidopsis tissue culture (Lall et al., 2004) . Higher levels of AtSBT1.1 expression may not have anything to do directly with shoot regeneration. However, higher levels of AtSBT1.1 expression might promote the proliferation of callus from which shoots are derived. Similar reasoning was used by Hanai et al. (2000) to explain the stimulatory effects of PSKs on somatic embryo formation in carrot. They concluded that PSKs might promote the proliferation of cells giving rise to somatic embryos, rather than influencing the formation of somatic embryos.