Expression of Arabidopsis thaliana HB17 gene in corn leads to improved sink potential

As a result of the large scale screening of candidate genes in transgenic corn, we identified an Arabidopsis thaliana gene HB17, a member of homeodomain-leucine zipper II (HD-Zip II) family of the plant transcriptional factors, which affects plant growth and leads to increase in ear size at silking. When expressed in corn, AtHB17 lacks the repression domain due to the corn-specific splicing mechanism and loses the ability to bind the co-repressors and affect transcription of the target genes.  The protein still can form homo-dimers as well as hetero-dimers with corn endogenous HD-Zip II proteins and bind to the target DNA sequences due to the presence of the functional leucine-zipper and DNA-binding domains.   We propose that AtHB17 expressed in corn mediates physiological effects through dominant-negative mechanism by attenuating transcriptional repression activity of endogenous corn HD-Zip II proteins.  We hypothesize that modulation of the activity of HD-ZIP II proteins leads to modulation of corn plant’s growth responses to environmental and developmental signals and, ultimately, to increased ear size, thus, providing opportunity for enhanced sink potential in corn plants.    Increased sink potential could be manifested through an increase in kernel weight or kernel number depending on the environmental conditions.