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

159 HANABA TARANU (HAN) Organizes Axis and Root Formation in the Early Embryo
Tal Nawy 1 , Chris Somerville 2 , Wolfgang Lukowitz 1
1
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 2 Carnegie Institution, Stanford, CA
Root formation in Arabidopsis is initiated early, coinciding with the elongation of the embryonic provascular cells
and the definition of a visible apical-basal axis. In this process, the hypophysis, or uppermost cell of the otherwise
extraembryonic filamentous suspensor, is recruited by the embryo and undergoes an asymmetric division that produces the
founder cell of the root meristem. We have identified mutations in the gene encoding the GATA-type transcription factor
HANABA TARANU (HAN) that have a dramatic and novel effect on axis and root formation in the early Arabidopsis
embryo. In han mutants, the hypophysis does not divide and the basal tier of the embryo is populated by fewer, abnormally
large cells. In contrast to other known mutants that lack basal pattern elements such as monopteros, han embryos often
generate an adventitious root in the central region of the embryo later in development. Analysis of basal marker gene
expression in the han background is consistent with this observation, as basal fates are not lost but appear to shift apically.
Interestingly, the embryonic auxin maximum as visualized by DR5:GFP also shifts from the hypophysis to the embryo
proper in han mutants. We are currently exploring the question of whether HAN is involved directly or indirectly with
auxin signaling, or if it operates in an independent pathway to pattern the early embryo.
160 Morphological changes in Arabidopsis by clock mutations lhy cca1 and prr9 prr7 prr5 in
light/dark cycles and continuous light condition
Kanae Niinuma 1 , Sumire Fujiwara 1 , Norihito Nakamichi 2 , Takeshi Mizuno 2 , Hiroshi Kamada 1 , Tsuyoshi Mizoguchi 1
1
University of Tsukuba, Japan , 2 University of Nagoya, Japan
LHY and CCA1 are shown to be closely associated with circadian clock function in Arabidopsis (1). The lhy cca1
mutation causes an extremely early flowering under short-days (1-3). We found that lhy cca1 flowered later than wildtype
plants under continuous light (LL). The lhy cca1 plants showed dark green and curled leaves and short hypocotyls
in LL. Molecular mechanisms of the dramatic morphological changes in light/dark (L/D) cycles and LL have not been
elucidated. PSEUDO RESPONSE REGULATORS (PRR1/TOC1, PRR3, PRR5, PRR7 and PRR9) are also shown to
be closely associated with circadian clock function in Arabidopsis (4). Triple loss-of-function of prr9 prr7 prr5 has been
shown to cause an arrhythmic expression of clock-controlled genes in LL (4). The prr9 prr7 prr5 showed a late flowering
phenotype and had pale green leaves and long petiols and hypocotyls in L/D cycles such as long-days and short-days
(4). Here we demonstrate that the prr9 prr7 prr5 plants had dark green/ curled leaves and short petiols in LL. These are
completely opposite to those in L/D cycles. The reversal of leaf color and petiol length phenotypes between L/D cycles
and LL is common in lhy cca1 and prr9 prr7 prr5. Molecular mechanisms underlying the reversal of the phenotypes will
be discussed.
1) Mizoguchi et al. Developmental Cell 2002
2) Mizoguchi et al. Plant Cell 2005
3) Fujiwara et al. Plant Biotech. 2005a, 2005b, 2005c
4) Nakamichi et al. Plant Cell Physiol. 2005