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

217 Regulation of inflorescence architecture in Arabidopsis
Harley Smith, Siddhartha Kanrar, Ricardo Junqueira, Moni Bhattacharya
Center for Plant Cell Biology, Dept. Botany and Plant Sciences, University of California, Riverside
Flowering is a major developmental phase change that transforms the fate of the shoot apical meristem (SAM) from
a leaf bearing vegetative meristem to that of a flower producing inflorescence meristem. In Arabidopsis, specifying
flowers and internodes involves the integration of environmental and endogenous floral promoting cues at the SAM. To
date, little is known about the molecular mechanisms that integrate the floral inductive cues to specify the inflorescence
pattern of growth. In Arabidopsis, two redundant functioning homeobox genes, PENNYWISE (PNY) and POUND-
FOOLISH (PNF), which are expressed in the vegetative and inflorescence SAM display a non-flowering phenotype during
inflorescence development. In addition, internode patterning is severely impaired in pny pnf plants. At the biochemical
level, PNY and PNF interact with another homeobox protein, SHOOTMERISTEMLESS (STM). Weak alleles of stm
display an inflorescence phenotype that is comparable to pny pnf double mutants, indicating that PNY-STM and PNF-
STM regulate inflorescence architecture. Genetic studies from our laboratory indicate that PNY-STM and PNF-STM
heterodimers function as co-factors for transcriptional complexes that regulate floral specification, internode patterning
and the maintenance of boundaries between initiating floral primordia and the inflorescence meristem.
218 Properties of Subtilase Genes Associated with Plant Development in Arabidopsis
Jianxiang Liu, Renu Srivastava, Sudhansu Dash, Ping Che, Stephen Howell
Plant Sciences Institute, Iowa State University
Subtilisin serine proteases (subtilases) are encoded by a family of 56 genes in Arabidopsis (Rautengarten et al.,
2005). We became interested in these genes when three of them (At1g01900, At4g26330 and At5g59120) appeared on
a list of genes upregulated in association with a major QTL conditioning shoot development in Arabidopsis (Lall et al.,
2004). We were awarded a NSF 2010 grant to understand the function of these three subtilase genes and seven others
(At5g51750, At1g32960, At1g32940, At4g21326, At5g59090, At1g20160, At5g59810 and At5g45650) that are regulated
during shoot, root or callus regeneration in culture. We are also part of a The Arabidopsis Subtilase Consortium (TASC,
http://csbdb.mpimp-golm.mpg.de/csbdb/dbcawp/psdb.html) that seeks to understand the function of all plant subtilase
genes. Many of the subtilase knockouts do not have obvious phenotypes (Rautengarten et al, 2005), hence, functional
studies are being directed toward understanding the properties of the genes and their gene products. Expression profiling
during organ regeneration revealed that At1g01900 is upregulated both during callus and shoot development. Two of the
genes (At1g32940 and At5g59810) are highly upregulated when root explants are placed on auxin-rich callus induction
medium. At4g21326, At5g59090 and At5g45650 are upregulated during shoot development and At5g51750, At4g26330
and At1g20160 are upregulated during root regeneration. The localization of subtilase gene expression based RT-PCR
analysis has been reported by Rautengarten et al. 2005. We expanded on that analysis using promoter: GUS constructs
and demonstrated that At1g01900 is expressed in newly formed callus and shoot primordia during organ regeneration
in culture. Many of the subtilase genes showed a strong disposition for expression in guard cells, such as At1g01900,
At1g32960, At5g51750, At5g59090, At5g59120 and At5g59810 while others such as At4g21326 and At1g20160, were
expressed in veins. Most of the subtilases in our study encode preproenzymes, which are predicted to be secreted proteins.
The exceptions are At4g21326 and At4g26330, which lack perceptible presequences. YFP-fusion constructs demonstrated
that, for example, the product of At1g01900 accumulates in the plasma membrane or apoplast. The subtilases are being
expressed in heterologous systems or as tap-tag constructs in Arabidopsis with the aim of characterizing the enzymatic
properties of the protein and the nature of the substrates.