Albino seedling lethality 4; Chloroplast 30S Ribosomal Protein S1 is Required for Chloroplast Ribosome Biogenesis and Early Chloroplast Development in Rice

Tingchen Ma,Zefu Li,Yuanlei Wang,Caijuan Zhang,Jiafa Xia,Kunneng Zhou,Peng Yun

doi:10.1186/s12284-021-00491-y

Tingchen Ma, Zefu Li + Show 5 more

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https://doi.org/10.1186/s12284-021-00491-y

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Abstract

BackgroundRibosomes responsible for transcription and translation of plastid-encoded proteins in chloroplasts are essential for chloroplast development and plant growth. Although most ribosomal proteins in plastids have been identified, the molecular mechanisms regulating chloroplast biogenesis remain to be investigated.ResultsHere, we identified albinic seedling mutant albino seedling lethality 4 (asl4) caused by disruption of 30S ribosomal protein S1 that is targeted to the chloroplast. The mutant was defective in early chloroplast development and chlorophyll (Chl) biosynthesis. A 2855-bp deletion in the ASL4 allele was verified as responsible for the mutant phenotype by complementation tests. Expression analysis revealed that the ASL4 allele was highly expressed in leaf 4 sections and newly expanded leaves during early leaf development. Expression levels were increased by exposure to light following darkness. Some genes involved in chloroplast biogenesis were up-regulated and others down-regulated in asl4 mutant tissues compared to wild type. Plastid-encoded plastid RNA polymerase (PEP)-dependent photosynthesis genes and nuclear-encoded phage-type RNA polymerase (NEP)-dependent housekeeping genes were separately down-regulated and up-regulated, suggesting that plastid transcription was impaired in the mutant. Transcriptome and western blot analyses showed that levels of most plastid-encoded genes and proteins were reduced in the mutant. The decreased contents of chloroplast rRNAs and ribosomal proteins indicated that chloroplast ribosome biogenesis was impaired in the asl4 mutant.ConclusionsRice ASL4 encodes 30S ribosomal protein S1, which is targeted to the chloroplast. ASL4 is essential for chloroplast ribosome biogenesis and early chloroplast development. These data will facilitate efforts to further elucidate the molecular mechanism of chloroplast biogenesis.

Highlights

Ribosomes responsible for transcription and translation of plastid-encoded proteins in chloroplasts are essential for chloroplast development and plant growth
Chlcontaining cells were few in number in leaves of the asl4 mutant compared to wild type (Fig. 1c, d)
To investigate the effect of the asl4 mutation on chloroplast development, we examined the ultrastructure of chloroplasts by transmission electron microscopy (TEM)

Summary

Introduction

Ribosomes responsible for transcription and translation of plastid-encoded proteins in chloroplasts are essential for chloroplast development and plant growth. Most ribosomal proteins in plastids have been identified, the molecular mechanisms regulating chloroplast biogenesis remain to be investigated. Plastids have their own genome and transcriptional and translational systems. Plastid ribosomes are the main sites of plastid protein translation in higher plants. Chloroplast biogenesis from a proplastid to mature chloroplast requires three steps and involves different regulatory genes (Kusumi et al 2010). RpoTp, rpoA and rpoB, are abundant in the second step: establishment of the plastid transcription/translation apparatus (De Santis-MacIossek et al 1999; Kusumi et al 2004). Genes psaB, psbA, psbB, psbC, rbcL, rbcS, cab1R and cab2R

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