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

135 Discovering the function of WAVE-ARP2/3-generated actin filaments during plant cell
morphogenesis
Chunhua Zhang 1 , Taisiya Zakharova 1 , Jie Le 1 , Eileen Mallery 1 , Salah El-Din El-Assal 2 , Daniel Szymanski 1
1
Purdue University, 2 Cairo University
The leaf epidermis is a critical organ that regulates gas-exchange and water loss, as well as being the first line of
resistance against insect and pathogen attack. Epidermal cell functions are intimately tied to their complex shapes.
For example, the highly polarized pavement cells have a complex lobed structure that allows adjacent pavement cells
to interlock and tightly seal internal compartments from the external environment. Trichomes are branched, highly
polarized cells that protect the plant against insect attack. We are using both cell types as models to understand how the
actin and microtubule cytoskeletons are coordinated during epidermal morphogenesis. Actin Related Protein (ARP) 2/3
is a heteromeric 7 subunit complex that efficiently nucleates actin filaments. In plants ARP2/3 is required for polarized
trichome growth, as well as for the normal development of pavement cell shape and cell-cell adhesion. ARP2/3 requires
positive regulation by another heteromeric complex termed WAVE (Szymanski, 2005). Although Arabidopsis continues
to provide important information regarding the in vivo function of individual WAVE and ARP2/3 complex proteins
(Djakovic et al., 2006; Le et al., 2006), little is known about the cellular function of these important complexes and the
actin filaments that they generate. The combination of well characterized mutants and new cytological tools has allowed
us to identify the active pools of WAVE and ARP2/3 in growing epidermal cells. Cell fractionation, localization data,
and live cell imaging assays indicate that ARP2/3 functions are intimately linked to the positioning and biogenesis of the
centeral vacuole. We will present our data indicating that plants cells have multiple and unique uses for the evolutionarily
conserved WAVE and ARP2/3 complexes.
Szymanski (2005) Current Opinion Plant Biol. 8(1): 103-12
Dajakovic et al. (2006) Development 133: 1091-1100
Le et al. (2006) Current Biology 16:1-7
136 MIKC* MADS-box transcription factors contribute to late pollen development in
Arabidopsis
Benjamin Adamczyk, Donna Fernandez
University of Wisconsin-Madison, Madison, WI
The MIKC* clade of MADS-box genes in Arabidopsis consists of six members, whose function has not been
previously defined. Members of the MIKC* clade are structurally similar to the well-characterized MIKC c MADS-box
factors, but have a less-conserved keratin-like domain and a longer intervening domain. Our lab has shown that all six
MIKC* genes are expressed in developing embryos (Lehti-Shiu et al. (2005) Plant Mol. Biol. 58: 89-107), and other
sources have shown that they are prominently expressed in mature pollen as well. To determine whether MIKC* factors
contribute to embryo or pollen function, we analyzed homozygous mutant plants for embryo and pollen defects. No
developmental changes were seen in the single mutants. Since functional redundancy is common with MADS-box factors,
we also generated double, triple, and quadruple mutant combinations. While embryo development was not affected in
any of the mutant combinations, we found that pollen function was compromised. Reciprocal crosses revealed that three
MIKC* factors play a redundant gametophyte-specific regulatory role in pollen development. Triple mutant pollen cannot
compete effectively with wild type or double mutant pollen, resulting in reduced transmission of the triple mutant allele
combination. We recovered plants homozygous for all three mutant alleles, which are viable but show fertility defects.
In vitro assays have shown that the rate of mutant pollen germination is reduced relative to wild type, and pollen tube
growth may also be defective. We are currently carrying out pollen competition assays with additional double, triple, and
quadruple mutant combinations to determine whether other pollen-expressing MADS-box factors contribute to pollen
function. Supported by USDA NRICGP (2001-35304-10887), and the UW-Madison Graduate School.