Discipline: Chemistry and Chemical Sciences
Subcategory: Biochemistry (not Cell and Molecular Biology and Genetics)
Brenda Eap - California State University, Los Angeles
Co-Author(s): Robert Luis Vellanoweth, California State University, Los Angeles
Flowering Locus T (FT) is a protein that is made in leaves and travels through plasmodesmata to the shoot apical meristem to induce flowering in Arabidopsis. The protein harbors a lipid binding domain, suggesting that the real flowering signal may in fact be a lipid-derived molecule. Previous studies done in our laboratory have suggested that leaf 13-lipoxygenase (LOX) is responsible for the synthesis of an oxylipin in leaves at the floral transition, leading to a potential lipid signal. We showed that a decline of ascorbate peroxidase (APx) and increase of H2O2 initiates an oxylipin pathway through plastid LOX activation during the floral transition. This suggests that the production of oxylipin signals is operative either locally within the leaf or at a distance following transport. Thus, such flowering-specific oxylipin signals may be carried by a lipid transfer protein (LTP) similar to the FT protein, the presumed ‘flowering hormone’. We found an induction of synthesis of two such LTPs in leaves at the floral transition. Based on our hypothesis that these LTPs may carry a similar flowering signal, we generated knockdown mutants of these LTPs in Arabidopsis plants. The RNAi knockdown mutants showed a longer lifespan pattern and perennial phenotype. After senescence, these mutant plants resurrect, forming new basal rosettes, suggesting that the LTPs are involved in meristem arrest. In further studies, we compared the flowering time of an FT mutant, ft-10, to the wild-type plant, observing that ft-10 flowers 4-5 weeks later than WT. To better understand the function of FT and our LTPs in the flower transition, we generated a double mutant plant expecting a further delay in flowering. Indeed, our double mutant plants exhibited a longer delay in flowering, as long as 7 months following the transition in wild-type plants and 6 months later than ft-10 plants. Uncommon phenotypes were also observed, such as a long woody stem with only leaves and no flowers and long bolts with only a few flowers at the tips. This delay suggests that the LTP and FT are both carriers of a lipid that is associated with flowering in Arabidopsis. To further study the role of the LTPs in our double mutants, RNA extractions followed by cDNA and RT-PCR will be done on the shoot apical meristem, bolts with floral meristems, bolts, leaves, and roots in different developmental stages to examine the expression levels of floral markers. We suspect low expression levels of certain flowering markers, leading to an accumulation of lipids that triggers late flowering in the double mutants altogether. Overall, studying these levels will help us understand the relationship between expression levels and phenotypic changes in our mutant plant.
References: Banuelos, R.G., Argumedo, R., Zhou, Feimeng., Vellanoweth, L. R., The development transition to flowering in Arabidopsis is associated with an increase in leaf chloroplastic lipoxygenase activity. Plant Science. 2008, 174, 366-373.
Funder Acknowledgement(s): This project is supported by Louis Stokes Alliances for Minority Participation (LSAMP) Program funded by NSF Grant (HRD-1302873).
Faculty Advisor: Robert Luis Vellnoweth, firstname.lastname@example.org
Role: The phenotypic comparisons and RNA extractions, followed by c-DNA and RT-PCR in tissues of interests in our double mutants to the ft-10 and wild-type plants.