Prof. Paul Jarvis BSc PhD
Professor of Plant Cell Biology
Prof. RP Jarvis
The biogenesis of chloroplasts and other plastids, including protein import mechanisms and regulation by the ubiquitin-proteasome system
Our research is focused on the biogenesis of chloroplasts and other
plastids in plants, particularly in relation to the import of nucleus-encoded
proteins and the role of the ubiquitin-proteasome system.
Chloroplast protein import
Plastids are a diverse family of plant organelles. The family includes
chloroplasts – the organelles responsible for photosynthesis – as well as a
range of non-photosynthetic variants such as starch-containing amyloplasts in
seeds, tubers and roots, carotenoid-rich chromoplasts in flowers and fruits,
and chloroplast-precursor organelles in dark-grown plants called etioplasts (Nat. Rev. Mol. Cell Biol. 2013, 14: 787-802). Most plastid proteins are encoded by the nuclear genome and synthesized
in the cytosol as precursors with N-terminal targeting signals called transit
peptides. Import of precursors into chloroplasts is mediated by the TOC and TIC
(Translocon at the Outer/Inner envelope membrane of Chloroplasts)
complexes (New Phytol. 2008, 179: 257-285). While much
progress has been made in understanding how the import machinery works,
substantial gaps remain in our knowledge; for example, the mechanisms
underlying the regulation of import are poorly understood. Our research seeks
to achieve a more complete understanding of chloroplast protein import
mechanisms, using a full spectrum of molecular, cellular, genetic, and
biochemical approaches. We have brought to bear the unique advantages offered
by the model plant Arabidopsis thaliana
(thale cress) as an experimental system in relation to plastid protein import
research. More recently, having identified potential practical applications of our
work, we have begun to also employ crop species as alternative models.
Control of plastid
biogenesis by the ubiquitin-proteasome system
recent work revealed that plastid biogenesis is directly regulated by the
ubiquitin-proteasome system (UPS), defining a new and fundamentally important
area of biology (Trends Cell Biol. 2013, 23: 399-408). In a screen for
extragenic suppressors of the Arabidopsis
plastid protein import mutation ppi1 (Science 1998, 282: 100-103), we identified SUPPRESSOR OF PPI1 LOCUS1
(SP1). SP1 encodes a RING-type ubiquitin E3 ligase in the plastid outer
membrane that selectively targets the TOC machinery for ubiquitination and
degradation. By controlling the levels of different TOC receptor isoforms, SP1
regulates which proteins are imported, and this in turn controls the plastid’s
proteome, functions and developmental fate (i.e.,
which type of plastid is formed) (Science 2012, 338: 655-659). This revealed
for the first time that the UPS directly regulates plastid development. It also
showed that plastid protein import is not merely a housekeeping process, but
rather it is one that can be dynamically regulated. In addition to its
fundamental importance, the discovery of SP1 suggested potential applications
in agriculture. In Arabidopsis, SP1
is important for developmental transitions in which plastids convert from one type
to another. As plastids and their interconversions are important throughout
plant development, manipulation of SP1 could conceivably find diverse
applications (e.g., during fruit
ripening in crops such as tomato and citrus, when chloroplasts transform into
chromoplasts, or during grain development in field crops such as wheat and
rice, when amyloplasts are formed). Manipulation of SP1 activity may allow
greater control over the developmental transitions of plastids.
Jarvis Group Members
Selected recent publications
Jarvis, P. and López-Juez, E. (2013) Biogenesis and homeostasis of chloroplasts and other plastids. Nat. Rev. Mol. Cell Biol. 14: 787-802.
Ling, Q. and Jarvis, P. (2013) Dynamic regulation of endosymbiotic organelles by ubiquitination. Trends Cell Biol. 23: 399-408.
Ling, Q., Huang, W., Baldwin, A. and Jarvis, P. (2012) Chloroplast biogenesis is regulated by direct action of the ubiquitin-proteasome system. Science 338: 655-659.
Jarvis, R.P., ed. (2011) Chloroplast Research in Arabidopsis: Methods and Protocols, Vols. I & II. Methods in Molecular Biology, Vols. 774 & 775. Humana Press, Totowa, NJ, USA.
Huang, W., Ling, Q., Bédard, J., Lilley, K. and Jarvis, P. (2011) In vivo analyses of the roles of essential Omp85-related proteins in the chloroplast outer envelope membrane. Plant Physiol. 157: 147-159.
Kasmati, A.R., Töpel, M., Patel, R., Murtaza, G. and Jarvis, P. (2011) Molecular and genetic analyses of Tic20 homologues in Arabidopsis thaliana chloroplasts. Plant J. 66: 877-889.
Aronsson, H., Combe, J., Patel, R., Agne, B., Martin, M., Kessler, F. and Jarvis, P. (2010) Nucleotide binding and dimerization at the chloroplast pre-protein import receptor, atToc33, are not essential in vivo but do increase import efficiency. Plant J. 63: 297-311.