Albino Leaf 1 that Encodes the Sole Octotricopeptide Repeat Protein Is Responsible for Chloroplast Development in Rice

Abstract

Chloroplast, the photosynthetic organelle in plants, plays a crucial role in plant development and growth through manipulating the capacity of photosynthesis. However, the regulatory mechanism of chloroplast development still remains elusive. Here, we characterized a mutant with defective chloroplasts in rice (Oryza sativa), termed albino leaf1 (al1), which exhibits a distinct albino phenotype in leaves, eventually leading to al1 seedling lethality. Electronic microscopy observation demonstrated that the number of thylakoids was reduced and the structure of thylakoids was disrupted in the al1 mutant during rice development, which eventually led to the breakdown of chloroplast. Molecular cloning revealed that AL1 encodes the sole octotricopeptide repeat protein (RAP) in rice. Genetic complementation of Arabidopsis (Arabidopsis thaliana) rap mutants indicated that the AL1 protein is a functional RAP. Further analysis illustrated that three transcript variants were present in the AL1 gene, and the altered splices occurred at the 39 untranslated region of the AL1 transcript. In addition, our results also indicate that disruption of the AL1 gene results in an altered expression of chloroplast-associated genes. Consistently, proteomic analysis demonstrated that the abundance of photosynthesis-associated proteins is altered significantly, as is that of a group of metabolism-associated proteins. More specifically, we found that the loss of AL1 resulted in altered abundances of ribosomal proteins, suggesting that RAP likely also regulates the homeostasis of ribosomal proteins in rice in addition to the ribosomal RNA. Taken together, we propose that AL1, particularly the AL1a and AL1c isoforms, plays an essential role in chloroplast development in rice.

The Rice Pentatricopeptide Repeat Gene TCD10 is Needed for Chloroplast Development under Cold Stress

“…Similarly, the significantly reduced transcripts of rbcL , an indicator for the accumulation of polysomes (Barkan 1993), chloroplast 16SrRNA, 23SrRNA and rps7, rps14, rps20 in the tcd10 mutants indicated that the tcd10 mutation affects the assembly and accumulation of plastid ribosomes, resulting in disruption of plastid translation. Similarly, the blockage of the chloroplast 16SrRNA maturation in Arabidopsis rap mutant (Kleinknecht et al 2014) and rice al1 mutant (Zhang et al 2016) leads to abnormal chloroplasts. Thus, TCD10 participates in not only the plastid translation, but also the assembly and the accumulation of plastid ribosomes.…”

A novel tetratricopeptide repeat protein, WHITE TO GREEN1, is required for early chloroplast development and affects RNA editing in chloroplasts

“…Deficient chloroplast development is always associated with abnormal expression of plastid genes ( Wang et al , 2016 a , 2016 b , Zhang et al , 2016 ). To analyze the effect of the wtg1 mutation on gene expression, we determined the transcription profiles of wild-type, wtg1 , and complemented seedlings using RNA-seq ( Supplementary Fig.…”

Integrating cell biology and proteomic approaches in plants

“…Shot gun proteomic analysis of al1 mutant indicated that AL1 controls chloroplast development through regulation of important chloroplast associated proteins such as subunits of different light reaction complexes including PSI, PSII, cytochrome b 6 /f, photosynthetic electron transport and F-type ATPase. Moreover, homeostasis of ribosomal proteins appeared to be important for chloroplast development [59]. Alteration of ribosomal proteins followed also chromoplast differentiation during orange fruit maturation as found by iTRAQ-based proteomic analysis.…”