Expression in multigene families. Analysis of chloroplast and mitochondrial proteases.
The proteolytic machinery of chloroplasts and mitochondria in Arabidopsis consists primarily of three families of ATP-dependent proteases, Clp, Lon, and FtsH, and one family of ATP-independent proteases, DegP. However, the functional significance of the multiplicity of their genes is not clear. To test whether expression of specific isomers could be differently affected by growth conditions, we analyzed transcript abundance following short-term exposure to different environmental stimuli, using 70-mer oligonucleotide arrays. This analysis revealed variability in the response to high light and different temperatures within members of each family. Thirty out of the 41 tested genes were up-regulated in response to high light, including both chloroplast and mitochondrial isozymes, whereas only six and five genes responded to either high or low temperature, respectively. The extent of response was variable, ranging from 2- to 20-fold increase in the steady-state levels. Absolute transcript levels of the tested genes, compiled from one-channel arrays, were also variable. In general, transcripts encoding mitochondrial isozymes were accumulated to a lower level than chloroplastic ones. Within the FtsH family, transcript abundance of most genes correlated with the severity of mutant phenotypes in the relevant genes. This correlation was also evident at the protein level. Analysis of FtsH isozymes revealed that FtsH2 was the most abundant species, followed by FtsH5 and 8, with FtsH1 being accumulated to only 10% of FtsH2 level. These results suggest that, unlike previous expectations, the relative importance of different chloroplast protease isozymes, evidenced by mutant phenotypes at least in the FtsH family, is determined by their abundance, and not necessarily by different specific functions or specialized expression under certain conditions.
Sinvany-Villalobo
Galit
G
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
Davydov
Olga
O
Ben-Ari
Giora
G
Zaltsman
Adi
A
Raskind
Alexander
A
Adam
Zach
Z
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D002736:Chloroplasts / Q000201:enzymology*; D017931:DNA Primers; D020224:Expressed Sequence Tags; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010446:Peptide Fragments / Q000737:chemistry; D010447:Peptide Hydrolases / Q000737:chemistry / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000235:genetics
D029681:Arabidopsis Proteins; D017931:DNA Primers; D010446:Peptide Fragments; D010447:Peptide Hydrolases