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

215 TRIDENT and VARICOSE encode components of the RNA decay machinery and are required
for normal leaf blade expansion
Leslie Sieburth, David Goeres, MaryLou Spencer, Weiping Zhang, Jaimie Van Norman
University of Utah
To understand the molecular basis for leaf blade development, we are characterizing mutants with leaf blade (and
vein patterning) defects. One of our mutants, trident (tdt), develops into very small sickly seedlings with multiple vascular
defects. In contrast to the wild type, which produces cotyledon veins composed of two to four complete areoles, tdt
cotyledons have no complete aeroles, and instead produced fork-like vein patterns. In addition, tdt mutants also have
vascular defects in the transition zone (hypocotyl apex) and occasional ectopic tracheary elements within the cotyledon
lamina. Aspects of the tdt phenotype are similar to that of varicose (vcs), a mutant that we characterized previously
(Deyholos et al., 2003 Devel 130:6577). To determine the molecular basis for the tdt phenotype, we mapped the gene to
chromosome 5. One candidate gene within our mapping interval contained a 50 nt deletion (in At5g13570). To confirm
that this was the gene that caused the tdt phenotype, we obtained a SALK insertion allele (exon 3) for this gene. The salk
allele (tdt-2) failed to complement the tdt-1 allele, indicating that the two lines have mutations in the same gene. The
TDT gene encodes a putative protein with two well-conserved N-terminal domains, a DCP2 domain, and an adjacent
NUDIX domain. This gene identity indicates that TDT encodes an mRNA decapping enzyme. VCS encodes a putative
protein with an N-terminal proline-rich domain followed by two WD domains, and shows similarity to the human RCD8
autoantigen. Recently, RCD8 was renamed GE-1/HEDLS, and was shown to be a component of P-Bodies and to bind
hDCP2 and hDCP1 (Yu et al., 2005 RNA 11:1795; Fenger-Gron 2005 Mol Cell 20:905). The phenotypic similarity of
vcs to tdt, and the molecular interaction between hVCS/HEDLS/GE-1 and hDCP2 suggests that VCS functions with
TDT in carrying out RNA decay.
216 Characterization of LcrTFL1, the Leavenworthia crassa TERMINAL FLOWER 1 ortholog
Marek Sliwinski, David Baum
University of Wisconsin Madison
TERMINAL FLOWER 1 (TFL1) encodes a small protein that is expressed in Arabidopsis inflorescence meristems
(IM) and functions to prevent the IM from adopting a floral fate by suppression of the floral meristem identity gene
LEAFY (LFY). tfl1 plants flower early and produce a determinate inflorescence in which the apical meristem is converted
to a terminal flower soon after the transition to flowering. In contrast, 35S::TFL1 lines are delayed in flowering and
the number of vegetative nodes increases 2-3 fold. These lines also have an increased number of paraclades, secondary
shoots with cauline leaves (I1) and novel secondary shoots without a subtending leaf (I1*). TFL1 and LFY homologs
have been identified in a number of species and have been postulated to play a role in the evolutionary diversification of
shoot architecture. Prior work with Leavenworthia crassa (Lcr) which produces flowers on long pedicels directly from
the rosette, showed that the LcrLFY gene differs from LFY in the regulation of TFL1. To test the hypothesis that there
has been molecular coevolution of LcrTFL1 and LcrLFY, and this played a role in the evolution of rosette flowering, we
cloned and characterized LcrTFL1 including introns and cis-regulatory regions. LcrTFL1 is able to rescue the premature
production of terminal flowers in tfl1 mutants indicating LcrTFL1 protein function and cis-regulation are largely conserved.
LcrTFL1 transgenic plants did differ from wildtype in other aspects of inflorescence architecture. As in 35S::TFL1
lines, LcrTFL1 causes an increase in the number of paraclades, yet unlike 35S::TFL1 this is predominantly in the form
of more I1 paraclades rather than I1* paraclades. This increase is dominant (it also occurs in LcrTFL1;TFL1 plants)
suggesting LcrTFL1 is more potent than TFL1 in maintaining the I1 developmental phase or less potent at suppressing
bract production. In addition, LcrTFL1 is different from 35S::TFL1 lines in that flowering time is not delayed. LcrTFL1
does not extend the vegetative phase suggesting LcrTFL1 expression before the transition to flowering is repressed. We
also rescued tfl1 using an EGFP:LcrTFL1 translational fusion construct allowing us to explore protein expression driven
by the LcrTFL1 cis-regulatory regions in an Arabidopsis genetic background.