75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

423 Protein Prenylation Process Negatively Regulates Abscisic Acid Signaling on Seed
Germination and Plant Drought Response in Arabidopsis thaliana
Xuejun Wang, Mark Running
Donald Danforth Plant Science Center
PLURIPETALA (PLP) encodes the α-subunit sharedbetween protein farnesyltransferase (PFT) and protein
geranylgeranyltransferase-I (PGGT-I) in Arabidopsisthaliana. Knockout of PLP (plp) show dramatically larger meristem,
increased floral organ number, ABA-sensitivity, and extreme drought tolerance. Knockout of the β-subunitof PFT (ERA1)
show milder developmental phenotypes and drought tolerance, but stronger ABA-hypersensitivity in seed germination
assays compared to plp. ABA response of stomataapertures of ggb, which is the knockout of PGGT-I β-subunit, were
very mild in phenotype. To learn the interactions of PLP and GGB in ABA response, we tested the development, seed
germination on ABA, drought stress response, and stomata aperture of single and double mutants of plp and ABA
biosynthesis and response mutants. Phenotypes of plp aba1-4, plp aba1-6, plp aba2-1, and plp aba3-1 show a synergistic
developmental phenotype of much smaller plants, suggesting that PLP does not mediate all ABA responses and that not
all PLP phenotypes depend on ABA. The double mutants also indicate that ABA is important for long term but not short
term drought tolerance of plp plants. Double plants of plp abi1-1, plp abi2-1, plp abi3-1, and plp abi4-101 showed same
developmental phenotype as plp alone. plp abi1-1 and plp abi2-1 doubles were sensitive to ABA on seed germination,
stomata aperture, and drought stress, while plp abi3-1 and plp abi5-1 doubles were insensitive to ABA in these assays.
Our result implicated that ABI1 and ABI2 act upstream of PLP and ABI3 and ABI5 act downstream of PLP. plp abi4-101
double showed similar results as wild type in all assays, suggesting they act in parallel pathways. Interestingly, abi5-1
plp plants show a dramatic rescue of plp developmental phenotypes, suggesting that abi5-1 acts downstream of plp in
pathways other than ABA response.
Corresponding author: Running P. M. Email: mrunning@danforthcenter.org
424 Prephenate dehydratase 1 Activity is Critical for Protection from UV Radiation Damage in
Etiolated Seedlings
Katherine Warpeha, Jack Gibbons, Andy Carol, Syed Lateef, Bob Lee, Lon Kaufman
University of Illinois at Chicago
Understanding the relationship between the synthesis of phenylalanine and the synthesis of UV screening pigments
will become increasingly important as the levels of incident UV-B radiation increase. We recently demonstrated BL or
ABA treatment of etiolated wt seedlings leads to the synthesis of phenylalanine via activation of a signal transduction
mechanism comprised of GCR1, GPA1 and Prephenate Dehydratase 1 (PD1). The phenylalanine produced by PD1
in etiolated seedlings is used by the phenylpropanoid pathway to produce a range of UV absorbing compounds, none
of which are produced in seedlings deficient in PD1, GPA1 or GCR1. Brief high energy radiation is lethal to etiolated
pd1, gcr1, and gpa1, yet wt and cry1cry2 and mutants in other members of the PD gene family (pd3,4,5 & 6) do not
exhibit lodging in response to the same treatment. The cotyledons of etiolated wt and pd1 mutants exhibit differences
in the distribution of UV absorbing compounds following brief exposure to UV (366 nm) light. Because they are slow
to accumulate chlorophyll and lack characteristic pink background autofluorescence, we examined the plastid status in
etiolated pd1 T-DNA insertion mutants. The cotyledons of etiolated pd1 insertion mutants have a proplastid in contrast
to etioplast present in wt seedlings. SEM data of etiolated wt seedlings demonstrates that a thick wax coat originates
at the tip of the cotyledon in both untreated and UV treated seedlings. In contrast, pd1 mutants do not accumulate this
material regardless of the light treatment. Osmium tetroxide staining confirms that the cotyledons of dark-grown pd1
insertion mutants have less cuticular surface wax and fewer long chain fatty acids, particularly at the very tip of the
cotyledon. SEM data also indicate that the cotyledons of UV treated pd1 mutants and not those of wt seedlings, accumulate
waxy material on both the adaxial and the abaxial surfaces. We are interested in the determining the roles of the PD1-
produced pigments and waxy materials in young etiolated seedlings, and how these PD-1-derived materials function in
UV-screening and protection.