Dr Qihua Ling

Research interests

Group Leader: Professor Paul Jarvis.

Research Areas:

1. Role of Ubiquitin-proteasome system in chloroplasts.

2. Chloroplast protein import and biogenesis.

3. Plant environmental stress tolerance related with chloroplast biogenesis and photosynthesis.

Protein import is critical to chloroplast biogenesis because most chloroplast proteins are imported from the cytosol. To uncover the regulatory mechanism of protein import, we conducted a screen for suppressors of a well-known Arabidopsis import mutant, ppi1, with a mutation in the receptor gene atTOC33. We identified sp1, which specifically suppresses the ppi1 phenotype in leaf colour and chloroplast protein import. Map-based cloning revealed that SP1 encodes a ubiquitin E3 ligase, a component of the UPS for protein degradation. SP1 is shown to be an integral chloroplast outer membrane protein. Biochemical studies showed that SP1 associates with TOC complexes and mediates ubiquitination of TOC components, promoting their degradation by the UPS. Mutant sp1 plants show retardation during de-etiolation and senescence, indicating that the regulation of protein import is involved in plastid developmental transitions. Recently, we have revealed a new role of SP1 in abiotic stress tolerance closely related to chloroplast protein import control. These results for the first time show that the UPS acts in chloroplast-resident proteins, regulating protein import to change the chloroplast proteome in response to developmental and environmental cues.