The Theobroma cacao B3 domain transcription factor TcLEC2 plays a duel role in control of embryo development and maturation.
BACKGROUND
The Arabidopsis thaliana LEC2 gene encodes a B3 domain transcription factor, which plays critical roles during both zygotic and somatic embryogenesis. LEC2 exerts significant impacts on determining embryogenic potential and various metabolic processes through a complicated genetic regulatory network.


RESULTS
An ortholog of the Arabidopsis Leafy Cotyledon 2 gene (AtLEC2) was characterized in Theobroma cacao (TcLEC2). TcLEC2 encodes a B3 domain transcription factor preferentially expressed during early and late zygotic embryo development. The expression of TcLEC2 was higher in dedifferentiated cells competent for somatic embryogenesis (embryogenic calli), compared to non-embryogenic calli. Transient overexpression of TcLEC2 in immature zygotic embryos resulted in changes in gene expression profiles and fatty acid composition. Ectopic expression of TcLEC2 in cacao leaves changed the expression levels of several seed related genes. The overexpression of TcLEC2 in cacao explants greatly increased the frequency of regeneration of stably transformed somatic embryos. TcLEC2 overexpressing cotyledon explants exhibited a very high level of embryogenic competency and when cultured on hormone free medium, exhibited an iterative embryogenic chain-reaction.


CONCLUSIONS
Our study revealed essential roles of TcLEC2 during both zygotic and somatic embryo development. Collectively, our evidence supports the conclusion that TcLEC2 is a functional ortholog of AtLEC2 and that it is involved in similar genetic regulatory networks during cacao somatic embryogenesis. To our knowledge, this is the first detailed report of the functional analysis of a LEC2 ortholog in a species other then Arabidopsis. TcLEC2 could potentially be used as a biomarker for the improvement of the SE process and screen for elite varieties in cacao germplasm.
Yufan
Y
Zhang
Adam
A
Clemens
Siela N
SN
Maximova
The Huck Institute of the Life Sciences, The Pennsylvania State University, 422 Life Sciences Building, University Park, PA 16802, USA. mjg9@psu.edu.
Mark J
MJ
Guiltinan
D000595:Amino Acid Sequence; D002099:Cacao / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D018548:Cotyledon / Q000235:genetics; D030541:Databases, Genetic; D056625:Endosperm / Q000196:embryology / Q000235:genetics; D005227:Fatty Acids / Q000096:biosynthesis; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary; D012038:Regeneration / Q000235:genetics; D012639:Seeds / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013329:Structure-Activity Relationship; D014170:Transformation, Genetic
D005227:Fatty Acids; D010940:Plant Proteins