PALE‐GREEN LEAF 1, a rice cpSRP54 protein, is essential for the assembly of the PSI‐LHCI supercomplex

Abstract

Although photosynthetic multiprotein complexes have received major attention, our knowledge about the assembly of these proteins into functional complexes in plants is still limited. In the present study, we have identified a chlorophyll‐deficient mutant, pale ‐ green leaf 1 ( pgl1 ), in rice that displays abnormally developed chloroplasts. Map‐based cloning of this gene revealed that OsPGL1 encodes a chloroplast targeted protein homologous to the 54‐kDa subunit of the signal recognition particle (cpSRP54). Immunoblot analysis revealed that the accumulation of the PSI core proteins PsaA and PsaB, subunits from the ATP synthase, cytochrome, and light‐harvesting complex (LHC) is dramatically reduced in pgl1 . Blue native gel analysis of thylakoid membrane proteins showed the existence of an extra band in the pgl1 mutant, which located between the dimeric PSII/PSI‐LHCI and the monomeric PSII. Immunodetection after 2D separation indicated that the extra band consists of the proteins from the PSI core complex. Measurements of chlorophyll fluorescence at 77 K further confirmed that PSI, rather than PSII, was primarily impaired in the pgl1 mutant. These results suggest that OsPGL1 might act as a molecular chaperone that is required for the efficient assembly and specific integration of the peripheral LHCI proteins into the PSI core complex in rice.

The role of chloroplast SRP54 domains and its C-terminal tail region in post- and cotranslational protein transportin vivo

“…This complex is composed of a subset of PSI core proteins and lacks the LHCI antenna proteins. Therefore, it resembles previously described PSI assembly intermediates in N. tabacum , Chlamydomonas reinhardtii and a recently identified rice mutant lacking cpSRP54 (Ozawa et al, 2010; Wittenberg et al, 2017; Gao et al, 2022). The specific accumulation of this assembly complex in the ffc mutant expressing cpSRP54 lacking its C-terminal region can be explained by our findings that this cpSRP54 variant still supports the cotranslational biogenesis of the PSI core proteins PsaA and PsaB, while the posttranslational transport of the LHCI antenna proteins is impaired.…”

“…This complex is composed of a subset of PSI core proteins and lacks the LHCI antenna proteins. Therefore, it resembles previously described PSI assembly intermediates in N. tabacum, Chlamydomonas reinhardtii and a recently identified rice mutant lacking cpSRP54 (Ozawa et al, 2010;Wittenberg et al, 2017;Gao et al, 2022).…”

A paler shade of green: engineering cellular chlorophyll content to enhance photosynthesis in crowded environments

“…In O. sativa two cpSRP54 paralog genes ( OscpSRP54a and OscpSRP54b ) were described (Shi et al ., 2020) and their individual inactivation resulted in PG plants. However, while the OscpSRP54a mutant displays only slightly reduced growth (Gao et al ., 2022), the OscpSRP54b mutation causes a severely compromised phenotype (Shi et al ., 2020), suggesting non‐redundant roles of the two protein isoforms. These same phenotypes were recently reproduced in a CRISPR/Cas9‐based knockout approach (Caddell et al ., 2023).…”

Transcriptomic Analysis Reveals Panicle Heterosis in an Elite Hybrid Rice ZZY10 and Its Parental Lines

“…Photosystem I (PSI) and photosystem II (PSII) protein complexes play a crucial role during photosynthesis [ 8 , 9 ]. All protein factors involved in the kinetic reactions of PSI and PSII complexes must be characterized in crops to improve photosynthetic efficiency and productivity [ 10 , 11 ]. It is speculated that improving ears photosynthesis in wheat will help increase the yield by 12–60% [ 12 , 13 ].…”