Title: An Essential Component in Chloroplast Development and Maintenance at Moderate High Temperature in Higher Plants: Chloroplast-targeted FtsH11 Proteases Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 30, 2010
Publication Date: N/A
Technical Abstract: Among the 12 predicted FtsH proteases in Arabidopsis, AtFtsH11 is the only metalloprotease targeting to both chloroplast and mitochondria and the only one essential for Arabidopsis plant to survive at moderate heat stress at all developmental stages. Under optimal conditions, atftsh11 mutants were indistinguishable from wild type plants in development and photosynthesis capacity. Cotyledons of ftsh11 seedlings germinated at 21ºC in dark contained normal etioplasts and developed normal chloroplast after exposure to light at the same temperature. However, the etiolated ftsh11 cotyledons failed to turn green after being transferred to light at 30ºC. TEM analysis showed that, instead developing thylakoid membranes, various forms of membrane stacks and lipid body were formed in the so-called chloroplasts. Further analysis revealed that the impacts of temperature on thylakoid membrane development in mutant started at around 25 ºC, a temperature considered in the normal range for Arabidopsis. Moreover, the thylakoids membranes of healthy chloroplasts in 21 ºC-grown ftsh11 plants started to disintegrate after exposure to 30ºC, a temperature at which WT plants developed normally. Overexpression of wildtype FtsH11 genes in ftsh11 was able to complement the thermosensitive phenotypes of mutant plants. These results suggest that FtsH11 plays critical roles in both the early stages of chloroplast biogenesis and maintaining thermostability of thylakoid membranes at moderate elevated temperatures. Several FtsH11 homologs with significant sequence similarity have been identified in several plant species. Overexpression of wild-type FtsH11 genes from pea (PsFtsH11), castor bean (RcFtsH11) and black cottonwood (PbFtsH11) in ftsh11 complemented the thermosensitive phenotypes of mutant plants, suggesting a conserved role of FtsH11 proteases in alleviation of damage caused by high temperatures in higher plants. Furthermore, targeted expression of AtFtsh11 in either chloroplast (cTP-FtsH11) or mitochondria (mTP-FtsH11) have showed that only chloroplast-targeted FtsH11 is essential for chloroplast biogenesis and maintaining thermostability of photosynthetic systems under high temperature stress.