Chloroplast SRP54s are Essential for Chloroplast Development in Rice

Yongfeng Shi,Xiangguang Lv,Yanlin Wei,Jian-Li Wu,Liangjian Li,Yan He,Xiaobo Zhang,Xia Xu

doi:10.1186/s12284-020-00415-2

Abstract

BackgroundThe chloroplast signal recognition particle 54 (cpSRP54) is known for targeting the light-harvesting complex proteins to thylakoids and plays a critical role for chloroplast development in Arabidopsis, but little is known in rice. Here, we reported two homologous cpSRP54s that affect chloroplast development and plant survival in rice.ResultsTwo rice cpSRP54 homologues, OscpSRP54a and OscpSRP54b, were identified in present study. The defective OscpSRP54a (LOC_Os11g05552) was responsible for the pale green leaf phenotype of the viable pale green leaf 14 (pgl14) mutant. A single nucleotide substitution from G to A at the position 278, the first intron splicing site, was detected in LOC_Os11g05552 in pgl14. The wild type allele could rescue the mutant phenotype. Knockout lines of OscpSRP54b (LOC_Os11g05556) exhibited similar pale green phenotype to pgl14 with reduced chlorophyll contents and impaired chloroplast development, but showed apparently arrested-growth and died within 3 weeks. Both OscpSRP54a and OscpSRP54b were constitutively expressed mainly in shoots and leaves at the vegetative growth stage. Subcellular location indicated that both OscpSRP54a and OscpSRP54b were chloroplast-localized. Both OscpSRP54a and OscpSRP54b were able to interact with OscpSRP43, respectively. The transcript level of OscpSRP43 was significantly reduced while the transcript level of OscpSRP54b was apparently increased in pgl14. In contrast, the transcript levels of OscpSRP54a, OscpSRP43 and OscpSRP54b were all significantly decreased in OscpSRP54b knockout lines.ConclusionOur study demonstrated that both OscpSRP54a and OscpSRP54b were essential for normal chloroplast development by interacting with OscpSRP43 in rice. OscpSRP54a and OscpSRP54b might play distinct roles in transporting different chloroplast proteins into thylakoids through cpSRP-mediated pathway.

Highlights

The chloroplast signal recognition particle 54 is known for targeting the light-harvesting complex proteins to thylakoids and plays a critical role for chloroplast development in Arabidopsis, but little is known in rice
Seven open reading frames (ORFs) were annotated within this region in the database of Rice Genome annotation Project, two of which (LOC_Os11g05552 and LOC_Os11g05556) were both annotated as hypothetical loci encoding for chloroplast signal recognition particle 54 (cpSRP54)
To determine the subcellular location, we first predicted their physical locations using the ChloroP program and the results showed that both OscpSRP54a and OscpSRP54b were located in chloroplasts (Supplementary Fig. 1)

Summary

Introduction

The chloroplast signal recognition particle 54 (cpSRP54) is known for targeting the light-harvesting complex proteins to thylakoids and plays a critical role for chloroplast development in Arabidopsis, but little is known in rice. The null mutant of Arabidopsis cpSRP43, chaos, exhibits pale green leaves including the first true leaves in the whole lifecycle, with elevated chlorophyll a/b ratio, but a normal level of reaction center proteins (Amin et al 1999; Klimyuk et al 1999). The chlorophyll synthesis and chloroplast development are impaired in company with altered expression of chlorophyll synthesis-associated genes in rice OscpSRP43 mutants, w67 and pgl, both of them show pale green leaves at all growth stages (Lv et al 2015; Ye et al 2018). Similar phenomena have been observed in tobacco, the cpSRP43 knockdown plants show lower chlorophyll contents in the RNAi canopy leaves with increased leaf-to-stem ratio, improved photosynthetic productivity and canopy biomass accumulation under high-density cultivation conditions (Kirst et al 2018)

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