Arabidopsis Chloroplast FtsH, var2 and Suppressors of var2 Leaf Variegation: a Review

Abstract

Variegation mutants are ideal model systems to study chloroplast biogenesis. We are interested in variegations whose green and white-sectored leaves arise as a consequence of the action of nuclear recessive genes. In this review, we focus on the Arabidopsis var2 variegation mutant, and discuss recent progress toward understanding the function of VAR2 and the mechanism of var2-mediated variegation. VAR2 is a subunit of the chloroplast FtsH complex, which is involved in turnover of the Photosystem II reaction center D1 protein, as well as in other processes required for the development and maintenance of the photosynthetic apparatus. The cells in green sectors of var2 have normal-appearing chloroplasts whereas cells in the white sectors have abnormal plastids that lack pigments and organized lamellae. To explain the mechanism of var2 variegation, we have proposed a threshold model in which the formation of chloroplasts is due to the presence of activities/processes that are able to compensate for a lack of VAR2. To gain insight into these activities, second-site suppressor screens have been carried out to obtain mutants with non-variegation phenotypes. Cloning and characterization of several var2 suppressor lines have uncovered several mechanisms of variegation suppression, including an unexpected link between var2 variegation and chloroplast translation.

Proteomic Analysis of Chloroplast-to-Chromoplast Transition in Tomato Reveals Metabolic Shifts Coupled with Disrupted Thylakoid Biogenesis Machinery and Elevated Energy-Production Components

“…The build up of the thylakoids requires the import of proteins within the plastid. A thylakoid Sec translocase subunit (SECA1, Solyc01g080840) is essential for chloroplast biogenesis (Liu et al, 2010b). Interestingly, the FtsH and EGY1 proteins decrease in abundance, mostly between the B and R stages, which correlates well with the dismantling of the thylakoid membranes, while SECA was present only at the MG stage, indicating an early end to the provision of material for thylakoid biogenesis.…”

A Comprehensive Analysis of Chromoplast Differentiation Reveals Complex Protein Changes Associated with Plastoglobule Biogenesis and Remodeling of Protein Systems in Sweet Orange Flesh

“…These Clp proteases formed a chaperone complex to drive the import of proteins into the plastids, cleave the transit peptide, and recycle plastid components. In Arabidopsis, knocking out most members of the Clp protease family results in reduced plant growth with pale-green or variegated leaf phenotype, indicating the crucial role of the Clp complex in chloroplast development (Meinke et al, 2008;Liu et al, 2010;Olinares et al, 2011). Previous studies have revealed that the Clp complex, one of the prominent complexes, increases in abundance during the transition from proplastids or etioplasts into chloroplasts (Kanervo et al, 2008;Majeran et al, 2010).…”

Rice Cytokinin GATA Transcription Factor1 Regulates Chloroplast Development and Plant Architecture

“…Instead, both Arabidopsis and rice show significant coexpression with tubulin-like Fts proteins found in the chloroplast thylakoid membrane that show homology to bacterial cell division genes (Jen et al, 2006;Jung et al, 2008a;Karamoko et al, 2011). Chloroplast division in plant cells requires the coordinated action of the tubulin-like FtsZ ring inside the chloroplast and the dynamin-like ring outside (Osteryoung et al, 1998;Osteryoung and McAndrew, 2001;Liu et al, 2010b;Pogson and Albrecht, 2011). The rice FtsZ gene (Os04g56970) is predicted to be involved in chloroplast division and was found to be significantly regulated by Cga1 expression in both microarray and quantitative reverse transcription (qRT)-PCR (Fig.…”