A research team led by Dr. GUO Fangqing from the Institute of Plant Physiology and Ecology (SIPPE), Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences reveals the importance of the PBR1-Ycf1 module for translational control of the concerted biogenesis of Photosystem I (PSI), cytochrome b6 (Cytb₆f) and NADH dehydrogenase (NDH) complexes. These three complexes have long been known to play a fundamental role in cyclic electron transfer around PSI during photosynthesis. Prior to this study, it is not known whether and how the biogenesis processes of these three complexes are finely coordinated.

Given that the photosynthetic complexes PSI, Cytb₆f and NDH each consists of both plastid- and nucleus-encoded subunits, the concerted accumulation of the various subunits of photosynthetic complexes in chloroplasts relies on a tight cooperation between the plastid and nucleus genomes.

In this study, scientists reported the identification of PHOTOSYSTEM BIOGENESIS REGULATOR 1 (PBR1). PBR1 is a nuclear-encoded chloroplast RNA-binding protein that regulates the concerted biogenesis of NDH, PSI and Cytb₆f complexes.

They measured the rate of translation of the chloroplast-encoded polypeptides as determined by pulse labeling experiments with both genetic loss-of-function and gain-of-function studies. They identified Ycf1, one of the two largest chloroplast genome-encoded open reading frames, as the direct downstream target protein of PBR1. Biochemical and molecular analyses reveal that PBR1 regulates the translation of Ycf1 by directly binding to its mRNA.

These findings demonstrate that the PBR1-Ycf1 module not only acts as a common fate determinant regulating biogenesis of NDH, PSI and Cytb₆f complexes but also perhaps functions as part of a developmental timer due to the strong light-inducible expressions of PBR1 during chloroplast development.

The study entitled “PBR1 selectively controls biogenesis of photosynthetic complexes by modulating translation of the large chloroplast gene Ycf1 in Arabidopsis” was published online in Cell Discovery.

This work was supported by grants from the Ministry of Science and Technology of China (2012CB944802) and the National Natural Science Foundation of China (91317305 and 31570260) and the Chinese Academy of Sciences.