Small chloroplast-targeted DnaJ proteins are involved in optimization of photosynthetic reactions in Arabidopsis thaliana

Abstract

BackgroundDnaJ proteins participate in many metabolic pathways through dynamic interactions with various components of these processes. The role of three small chloroplast-targeted DnaJ proteins, AtJ8 (At1 g80920), AtJ11 (At4 g36040) and AtJ20 (At4 g13830), was investigated here using knock-out mutants of Arabidopsis thaliana. Photochemical efficiency, capacity of CO2 assimilation, stabilization of Photosystem (PS) II dimers and supercomplexes under high light illumination, energy distribution between PSI and PSII and phosphorylation of PSII-LHCII proteins, global gene expression profiles and oxidative stress responses of these DnaJ mutants were analyzed.ResultsKnockout of one of these proteins caused a series of events including a decrease in photosynthetic efficiency, destabilization of PSII complexes and loss of control for balancing the redox reactions in chloroplasts. Data obtained with DNA microarray analysis demonstrated that the lack of one of these DnaJ proteins triggers a global stress response and therefore confers the plants greater tolerance to oxidative stress induced by high light or methyl viologen treatments. Expression of a set of genes encoding enzymes that detoxify reactive oxygen species (ROS) as well as a number of stress-related transcription factors behaved in the mutants at growth light similarly to that when wild-type (WT) plants were transferred to high light. Also a set of genes related to redox regulation were upregulated in the mutants. On the other hand, although the three DnaJ proteins reside in chloroplasts, the expression of most genes encoding thylakoid membrane proteins was not changed in the mutants.ConclusionIt is proposed that the tolerance of the DnaJ protein knockout plants to oxidative stress occurs at the expense of the flexibility of photosynthetic reactions. Despite the fact that the effects of the individual protein knockout on the response of plants to high light treatment are quite similar, it is conceivable that both specific- and cross-talk functions exist between the three small chloroplast-targeted DnaJ proteins, AtJ8, AtJ11 and AtJ20.

A Small Zinc Finger Thylakoid Protein Plays a Role in Maintenance of Photosystem II in Arabidopsis thaliana

“…Although we cannot rule out the possibility that LQY1 is directly involved in ROS detoxification, the comigration of LQY1 with CP43-less PSII monomer is consistent with the role of LQY1 in PSII repair and reassembly. Further studies of LQY1 and other thylakoid accessory proteins should lead to a more detailed understanding of the dynamics of PSII core protein repair and assembly (Yokthongwattana et al, 2001;Mulo et al, 2008;Chen et al, 2010).…”

“…The repair cycle of PSII requires the participation of more than 25 auxiliary proteins (Mulo et al, 2008), including heat shock protein 70 family members, PSII 22 kDa protein (PSB29), LOW PSII ACCUMULATION protein (LPA1), which are essential for repair of PSII, and small J-domain proteins AtJ8, AtJ11, and AtJ20 (Schroda et al, 1999;Yokthongwattana et al, 2001;Keren et al, 2005;Peng et al, 2006;Chen et al, 2010).…”

Nucleoid-Enriched Proteomes in Developing Plastids and Chloroplasts from Maize Leaves: A New Conceptual Framework for Nucleoid Functions

“…Plastid DnaJ(-like) proteins play diverse roles in plastid biogenesis, including plastid division and protein assembly and disassembly, and the DnaJ domain is best known as a nucleotide-exchange factor of ATP-dependent chaperones such as HSP70 (Albrecht et al, 2008;Chen et al, 2010). Other well-studied plastid DnaJ domain proteins include Rubisco assembly factor BSD2 (Brutnell et al, 1999) and ARC6, involved in plastid division (Glynn et al, 2009).…”

Evolution of C4 Photosynthesis in the GenusFlaveria: How Many and Which Genes Does It Take to Make C4?

“…Several DnaJ proteins with unknown function behaved similarly. Plastidic DnaJ proteins are involved in the stabilization of thylakoid membrane complexes like photosystem II (Chen et al, 2010). Several proteases belonging to Clp (ClpR1 and ClpP5) and FtsH (FtsH8, VAR1, and VAR2) complexes were upregulated, too.…”