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

421 Arabidopsis Receptor-like Cytoplasmic Kinases Involved in Growth and Development
Carl-Erik Tornqvist, Ronan O'Malley, Jenny Liu, Anthony Bleecker, Sara Patterson
University of Wisconsin, Madison
Plant receptor-like kinases (RLKs) have been implicated in growth and development, disease resistance, stress
response, and self-incompatibility. The Arabidopsis RLK gene family contains over 600 members, yet only a handful
have known functions. Using a high-throughput reverse genetics approach, we have isolated homozygous T-DNA lines
spanning 26 subfamilies and covering much of four. Specifically, we have focused on receptor-like cytoplasmic kinases
(RLCKs), which lack the transmembrane and extracellular domains of typical RLKs. These proteins may function as
intermediate signaling components between other kinase players. Such interactions have been shown in pathways of
Pseudomonas resistance and self-incompatibility. All mutant lines have been screened for alterations in growth and
development and responses to phytohormones, including: auxin, cytokinin, gibberellin, and ethylene.
Currently, only three single mutant lines and one double mutant display growth defects. All four mutant lines have
disruptions in RLCKs; all from subfamily RLCK VII. Two single mutants have altered root and hypocotyl growth. A
double homozygous mutant, which was generated between two closely related mutant lines with no phenotypes, appears
to have delayed flowering, evidenced by much larger rosettes, thicker primary shoot, and longer time to bolting than wild
type. Of particular interest is a single homozygous mutant we call lacy, which displays asymmetric leaf morphology,
reduced leaf size, small stature, altered apical dominance, and irregular trichomes with supernumerary branching. We
have conducted preliminary phenotypic characterizations of all four mutant lines, with most emphasis on the lacy mutant.
To answer the question of why lacy has altered leaf development, epidermal cell size and cell number were compared
to wild type. The pattern of cell division was also examined in the mutant and wild type by introgression of a construct
harboring the Cyclin1a promoter with the GUS reporter (Ferreira, 1994). In addition to phenotypic characterization of
lacy, genetic interactions with the most closely related RLKs were also analyzed. We will present the phenotypes of
these four mutants, some expression data culled from microarray experiments, and summarize genotyping results for
the entire homozygous set.
422 Functional Genomic Analysis of the 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE
(ACS) Gene Family Members in Arabidopsis thaliana: Construction and Characterization of
a pentuple Mutant
Atsunari Tsuchisaka 1 , Hailing Jin 4 , Jose Alonso 2, 3 , Joseph Ecker 2 , Athanasios Theologis 1
1
UCB/USDA Plant Gene Expression Center, Albany, CA 94710, USA, 2 Salk Institute for Biological Studies, La
Jolla, CA 92037, USA, 3 Department of Genetics, North Carolina State University, Raleigh, NC 27695, USA,
4
Department of Plant Pathology, University of California at Riverside, CA 92521, USA
1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE (ACS) catalyzes the rate-limiting step in the ethylene
biosynthetic pathway in plants. The Arabidopsis genome encodes nine ACS polypeptides that form eight functional
(ACS2, ACS4-9, ACS11) and one non-functional (ACS1) homodimers. The ACS polypeptides have also the capacity
to form active (17) and inactive (25) heterodimers. Herein, we report the identification and characterization of T-DNA
insertion lines for five (ACS2, ACS4, ACS5, ACS6 and ACS9) among the nine ACS genes. All single insertion alleles
show an enhanced plant size and the acs6-1, acs9-1 mutants flower earlier than the wild type plants. Subsequently, we
generated 19 double, 25 triple, 16 quadruple, and 4 pentuple mutants, using various insertional alleles of the single T-
DNA lines. There is a progressive enhancement in plant height in the higher order mutations. A pentuple mutant (acs2-1
acs4-1 acs5-2 acs6-1 acs9-1) was phenotypically characterized in a great detail and its phenotype was compared to those
of two ethylene perception mutants, etr1-1 and ein2-5. The pentuple mutant forms a normal hook, flowers earlier and is
taller than the wild type. The sizes of its siliques, flowers, seeds, leaves are the same as the wild type. Its responses to
the infection with the bacteria pathogens, Xanthomonas campestris pv. vesicatoria (Xcv), Xanthomonas campestris pv.
campestris (Xcc), necrotropic fungus Alternaria brassicicola and oil rape mosaic virus (ORMV) are the same as the wild
type. Inactivation of the Arabidopsis ACS capacity by eighty percent in the pentuple mutant yields a perfectly functional
plant and does not delay its senescence. These observations provide molecular insight into the unique and overlapping
functions of the ACS gene family members in Arabidopsis. The pentuple mutant also provides the framework for future
construction of a “Yang cycle”-dependent null ethylene producing Arabidopsis plant, to ascertain whether ethylene is
required for plant growth and development.