Molecular Plant Advance Access originally published online on September 18, 2009
Molecular Plant 2009 2(6):1211-1222; doi:10.1093/mp/ssp077
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Arabidopsis FtsZ2-1 and FtsZ2-2 Are Functionally Redundant, But FtsZ-Based Plastid Division Is Not Essential for Chloroplast Partitioning or Plant Growth and Development
a Department of Plant Biology, 166 Plant Biology Bldg, Michigan State University, East Lansing, MI 48824-1312, USA
b Cell and Molecular Biology Program, Michigan State University, East Lansing, MI 48824, USA
c Department of Energy–Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
d Genetics Program, Michigan State University, East Lansing, MI 48824, USA
e Biochemistry and Molecular Biology Program, Michigan State University, East Lansing, MI 48824, USA
f Present address: The Salk Institute for Biological Studies, Plant Molecular and Cellular Biology Laboratory, La Jolla, CA 92037, USA
g Present address: Mycobacteria and Brucella Section, NVSL/APHIS/USDA, 1920 Dayton Ave, Ames, IA 50010, USA
1 To whom correspondence should be addressed. E-mail osteryou{at}msu.edu, fax 517-353-1926, tel. 517-355-4685.
FtsZ1 and FtsZ2 are phylogenetically distinct families of FtsZ in plants that co-localize to mid-plastid rings and facilitate division of chloroplasts. In plants, altered levels of either FtsZ1 or FtsZ2 cause dose-dependent defects in chloroplast division; thus, studies on the functional relationship between FtsZ genes require careful manipulation of FtsZ levels in vivo. To define the functional relationship between the two FtsZ2 genes in Arabidopsis thaliana, FtsZ2-1 and FtsZ2-2, we expressed FtsZ2-1 in an ftsZ2-2 null mutant, and vice versa, and determined whether the chloroplast division defects were rescued in plants expressing different total levels of FtsZ2. Full rescue was observed when either the FtsZ2-1 or FtsZ2-2 level approximated total FtsZ2 levels in wild-type (WT). Additionally, FtsZ2-2 interacts with ARC6, as shown previously for FtsZ2-1. These data indicate that FtsZ2-1 and FtsZ2-2 are functionally redundant for chloroplast division in Arabidopsis. To rigorously validate the requirement of each FtsZ family for chloroplast division, we replaced FtsZ1 with FtsZ2 in vivo, and vice versa, while maintaining the FtsZ level in the transgenic plants equal to that of the total level in WT. Chloroplast division defects were not rescued, demonstrating conclusively that FtsZ1 and FtsZ2 are non-redundant for maintenance of WT chloroplast numbers. Finally, we generated ftsZ triple null mutants and show that plants completely devoid of FtsZ protein are viable and fertile. As plastids are presumably essential organelles, these findings suggest that an FtsZ-independent mode of plastid partitioning may occur in higher plants.
Key Words: Chloroplast • plastid division • FtsZ • ARC6 • PDV1