LEAFY COTYLEDON2encodes a B3 domain transcription factor that induces embryo development

Abstract

The Arabidopsis LEAFY COTYLEDON2 (LEC2) gene is a central embryonic regulator that serves critical roles both early and late during embryo development. LEC2 is required for the maintenance of suspensor morphology, specification of cotyledon identity, progression through the maturation phase, and suppression of premature germination. We cloned the LEC2 gene on the basis of its chromosomal position and showed that the predicted polypeptide contains a B3 domain, a DNA-binding motif unique to plants that is characteristic of several transcription factors. We showed that LEC2 RNA accumulates primarily during seed development, consistent with our finding that LEC2 shares greatest similarity with the B3 domain transcription factors that act primarily in developing seeds, VIVIPAROUS1/ABA INSENSITIVE3 and FUSCA3. Ectopic, postembryonic expression of LEC2 in transgenic plants induces the formation of somatic embryos and other organ-like structures and often confers embryonic characteristics to seedlings. Together, these results suggest that LEC2 is a transcriptional regulator that establishes a cellular environment sufficient to initiate embryo development.

Heterologous expression of the BABY BOOM AP2/ERF transcription factor enhances the regeneration capacity of tobacco (Nicotiana tabacum L.)

“…Here we show that ectopic BBM expression in combination with cytokinin is suYcient to induce somatic embryogenesis in tobacco seedlings, suggesting that BBM acts by bypassing the need for one or more of these plant growth regulators. Spontaneous somatic embryogenesis has been observed in a number of Arabidopsis mutants, including the gain-of-function LEAFY COT-YLEDON1 (LEC1) and LEC2 mutants (Lotan et al 1998;Stone et al 2001) and the pickle (pkl) loss-offunction mutant (Ogas et al 1997). Both LEC proteins and PKL appear to function in the context of hormone signalling pathways to activate spontaneous somatic embryogenesis.…”

“…(Kakimoto 1996;Lotan et al 1998;Hewelt et al 2000;Banno et al 2001;Stone et al 2001;Boutilier et al 2002;Zuo et al 2002). Most of these genes have been identiWed in Arabidopsis [Arabidopsis thaliana (Heyhn) L.] and many of them encode transcription factors or proteins involved in signal transduction.…”

Seed dormancy and germination

“…All four abi3, lec1, lec2 and fus3 mutants are severely affected in seed maturation and share some common phenotypes, such as decreased dormancy at maturation (Raz et al, 2001) and reduced expression of seed storage proteins (Gutierrez et al, 2007). However, they also show specific phenotypes, such as the absence of chlorophyll degradation in the dry seed (abi3), a reduced sensitivity to ABA (abi3 and, to a lesser extent, lec1), the accumulation of anthocyanins (fus3, lec1, and, to a lesser extent, lec2), an intolerance to desiccation (abi3, fus3, and lec1), or defects in cotyledon identity (lec1, fus3, and lec2) (Bäumlein et al, 1994; Keith et al, 1994;Meinke et al, 1994;Parcy et al, 1994;Parcy & Giraudat, 1997;Luerssen et al, 1998;Vicient et al, 2000;Raz et al, 2001;Stone et al, 2001; Kroj et al, 2003). It was recently shown that several of the fus3 phenotypes are due to pleiotropic effects caused by truncated gene products of the mutant alleles.…”

“…ABA-INSENSITIVE3 (ABI3), FUSCA3 (FUS3) and LEAFY COTYLEDON (LEC1 and LEC2) are four key regulators that play prominent roles in controlling mid-and late seed development (Meinke et al, 1994;Raz et al, 2001). ABI3, FUS3 and LEC2 encode related plant-specific transcription factors containing the conserved B3 DNA binding domain (Giraudat et al, 1992;Luerssen et al, 1998;Stone et al, 2001), whereas LEC1 encodes a HAP3 subunit of the CCAAT binding transcription factor (CBF, also known as NF-Y (Lotan et al, 1998)). All four abi3, lec1, lec2 and fus3 mutants are severely affected in seed maturation and share some common phenotypes, such as decreased dormancy at maturation (Raz et al, 2001) and reduced expression of seed storage proteins (Gutierrez et al, 2007).…”

BABY BOOM target genes provide diverse entry points into cell proliferation and cell growth pathways

“…Ectopic expression of the seed-specific CCAAT-box binding factor LEAFY COTYLEDON1 (LEC1) and the B3 domain transcription factor, LEC2 also promote somatic embryo formation on seedlings (Lotan et al 1998;Stone et al 2001). Loss-of-function lec1 and lec2 mutants are impaired in embryo identity and maturation, indicating their broad role as regulators of embryo development (reviewed in Harada 2001).…”