15th International Conference on Arabidopsis Research - TAIR

T02-099
Regulatory Mechanisms in Shoot and Root
Development
Jennifer C. Fletcher(1), Leor Williams(1), Stephen P. Grigg(1), Mingtang Xie(2), Sioux
Christensen(2)
1-USDA/UC Berkeley Plant Gene Expression Center, Albany, CA 94710 USA
2-Dept. of MCD Biology, UCLA, Los Angeles, CA 90095 USA
Plant architecture is the product of shoot and root apical meristems, which
form from opposite poles during embryogenesis and remain active throughout
the life of the plant. Shoots and roots grow in very different environments,
and thus respond to different exogenous and endogenous cues. They
also have different ways of making lateral organs, with shoots producing
leaves and flowers in stereotypical arrangements at the very tip, and primary
roots forming lateral roots in a stochastic fashion at some distance from
the apex. However, recent experiments have revealed that shoots and roots
share some common molecular mechanisms for regulating their growth
and development, and their responses to their environments. As part of our
ongoing effort to understand the molecular processes that regulate Arabidopsis
shoot apical meristem function, we are characterizing a dominant,
activation-tagged mutant called jabba-1D (jba-1D) that has defective shoot
apical meristem (SAM) activity and lateral organ polarity. The SAMs of jba-1D
plants enlarge progressively beginning during embryogenesis, leading to
the splitting of the shoot apex during the vegetative phase and eventually to
inflorescence stem fasciation. This phenotype is associated with broadening
of the WUS and CLV3 expression domains, and with abnormally high levels
of WUS transcription in the SAM. jba-1D plants also develop extra vascular
bundles in their stems, and form radialized leaves and gynoecia. We show
that the jba-1D phenotypes are caused by over-expression of miR166g, one
of nine microRNAs encoded in the Arabidopsis genome that are complementary
to the class III homeodomain-leucine zipper (HD-Zip) developmental
regulatory transcription factor family. miR166g over-expression in jba-1D
plants requires DICER-LIKE1 (DCL1) activity, and alters the expression of the
HD-Zip genes REVOLUTA, PHABULOSA, and PHAVOLUTA.
T02 Development 2 (Shoot, Root)
T02-100
Comparative chloroplast proteomics of a cpSRP54
deletion mutant in Arabidopsis thaliana
Heidi Rutschow(1), Jimmy Ytterberg(1), Robert Nilsson(1), Klaas J. van Wijk(1)
1-Department of Plant Biology, Cornell University, Ithaca, NY 14853
Chloroplasts are essential organelles containing some 3000 nuclear-encoded
proteins, ~120 chloroplast-encoded proteins and an internal thylakoid membrane
system. Protein sorting, assembly and proteolytic disposal within this
plastid are critical for plant development and function. Specifically, the targeting
machinery must ensure proper coordination and insertion of hundreds
of known and unknown nuclear and chloroplast-encoded thylakoid proteins,
while the proteolytic machinery must maintain cellular housekeeping and
remove aggregated and damaged proteins. Different protein sorting routes
and their protein components have been discovered within the chloroplast,
with just a handful of identified substrates for each of these routes.
This poster will describe our preliminary data on the effect of
deletion of the cpSRP54 subunit on the chloroplast proteome in Arabidopsis
thaliana. cpSRP54 has been demonstrated to be involved in membrane
targeting of selected nuclear-encoded hydrophobic chlorophyll a/b binding
thylakoid membrane proteins. cpSRP54 is also implied in insertion of several
hydrophobic chloroplast-encoded membrane proteins. However, the deletion
mutant is viable, showing slightly pale leaves, reduced biomass and a delay
in flowering time. Given that the thylakoid membrane proteome contains
hundreds of membrane proteins, it is expected that other proteins also depend
on cpSRP54. However, as the deletion mutant is viable, with a relative
mild chloroplast phenotype, it is logic to postulate that other sorting pathways
or mechanisms can compensate for the loss of cpSRP54. Also, protein aggregates
resulting from miss-targeting are possibly removed by up-regulation
of proteolytic activity.
I will present data concerning the thylakoid proteome, as well as
the stromal proteome, using different fractionation techniques, mass spectrometry
and Western blotting. In addition, I will discuss the relation between
expression of protein targeting components and the developmental stage of
the leaf.
Amin, et al. (1999). Plant Physiol 121, 61-70.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin