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Members of the AP2 family of transcription factors, such as BABY BOOM (BBM), play important roles in cell proliferation and embryogenesis in Arabidopsis thaliana (AtBBM) and Brassica napus (BnBBM) but how this occurs is not understood. We have isolated three AP2 genes (GmBBM1, GmAIL5, GmPLT2) from somatic embryo cultures of soybean, Glycine max (L.) Merr, and discovered GmBBM1 to be homologous to AtBBM and BnBBM. GmAIL5 and GmPLT2 were homologous to Arabidopsis AINTEGUMENTA-like5 (AIL5) and PLETHORA2 (PLT2), respectively. Constitutive expression of GmBBM1 in Arabidopsis induced somatic embryos on vegetative organs and other pleiotropic effects on post-germinative vegetative organ development. Sequence comparisons of BBM orthologues revealed the presence of ten sequence motifs outside of the AP2 DNA-binding domains. One of the motifs, bbm-1, was specific to the BBM-like genes. Deletion and domain swap analyses revealed that bbm-1 was important for somatic embryogenesis and acted cooperatively with at least one other motif, euANT2, in the regulation of somatic embryogenesis and embryo development in transgenic Arabidopsis. The results provide new insights into the mechanisms by which BBM governs embryogenesis.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-010-9674-8) contains supplementary material, which is available to authorized users.

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Large differences in winter hardiness exist among alfalfa (Medicago sativa L.) cultivars, but the physiological and molecular bases for these differences are not understood. Our objective was to determine how raffinose family oligosaccharide (RFO) accumulation and steady state mRNA levels for galactinol synthase (GaS) in roots relate to genetic variation in alfalfa winter survival. A GaS cDNA was isolated that possesses over 70% identity with GaS clones from other plant species. Induction of GaS transcripts in crowns of winter hardy alfalfa cultivars occurred within 8 h of exposure to 2°C, and was intensified by exposing plants to −2°C for 2 wk. Galactinol synthase transcripts increased in November in crown and root tissues of winter hardy alfalfa plants. This increase was accompanied by large increases in root RFO concentrations between October and December. A close positive association between RFO accumulation in roots in December and genetic differences in winter survival was observed in these alfalfa populations. Although roots and crowns of nondormant alfalfa cultivars accumulated both GaS transcripts and RFO, accumulation was delayed until December and these cultivars did not survive winter. Understanding the mechanisms regulating GaS gene expression and subsequent RFO accumulation in roots and crowns provides opportunity to genetically improve alfalfa winter hardiness.

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