A naturally occurring conditional albino mutant in rice caused by defects in the plastid-localized OsABCI8 transporter

Abstract

A wide range of molecules are transported across membranes by the ATP binding cassette (ABC) transporters. Plants possess a collection of ABC proteins bearing similarities to the components of prokaryotic multi subunit ABC transporters, designed as ABC group I. However the functions of most of them are not well understood. Here, we characterized a naturally occurring rice mutant that exhibited albino phenotype under continuous rainy days in the field, but gradually recovered to normal green after the rainy season. Molecular and genetic analyses revealed that the phenotypes were caused by a mutation in the OsABCI8 that encoded a member of the ABCI family. Subcellular localization demonstrated that OsABCI8 is a chloroplast ABC transporter. Expression of OsABCI8 is significantly enhanced in rainy days compared to sunny days. Besides defects in chloroplast development and chlorophyll biosynthesis, the mutant phenotype is accompanied by a higher accumulation of iron, suggesting that OsABCI8 is involved in iron transportation and/or homeostasis in rice. Our results demonstrate that OsABCI8 represents a conserved ABCI protein involved in transition metals transportation and/or homeostasis and suggest an important role of the plastid-localized OsABCI8 for chloroplast development.

TSC1 enables plastid development under dark conditions, contributing to rice adaptation to transplantation shock

“…n, the number of tested seedlings in each treatment. homologous to AtNAP14, and mutations in the AtNAP14 and LOC_Os11g29850 coding regions have been reported to cause albino leaves (Shimoni-Shor et al 2010;Zeng et al 2017). Although previous studies did not support the hypothesis that this gene and its related albino phenotype are regulated by light/dark conditions, LOC_Os11g29850 is a strong candidate for TSC1.…”

“…All recombinant individuals were homozygous for the mutation type (T), indicating that this G‐to‐T transversion co‐segregated with the albino phenotype. LOC_Os11g29850 encodes a chloroplast‐located noncanonical ABC protein homologous to AtNAP14 , and mutations in the AtNAP14 and LOC_Os11g29850 coding regions have been reported to cause albino leaves (Shimoni‐Shor et al ; Zeng et al ). Although previous studies did not support the hypothesis that this gene and its related albino phenotype are regulated by light/dark conditions, LOC_Os11g29850 is a strong candidate for TSC1 .…”

“…TSC1-mediated iron and copper balance is required for adaptation to transplantation shock AtNAP14 and its orthologs are responsible for metal homeostasis (Shimoni-Shor et al 2010;Zeng et al 2017). Therefore, we compared the concentrations of biologically relevant transition metals in the tsc1-KO mutant and WT under normal growth conditions (i.e., light conditions) and dark conditions.…”

“…In our study, we found that although TSC1 regulates the homeostasis of multiple metals, the iron and copper balance has the predominant effect on TSC1‐mediated plastid development. Strikingly, the iron concentration was increased in the shoot of the atnap14 mutant and in the leaf of the abci8 mutant (Shimoni‐Shor et al ; Zeng et al ), but in the tsc1 mutant, the iron concentration was decreased in the leaf under dark conditions and was not significantly changed under light conditions (Figure ). The expression patterns of iron‐deficiency‐response genes supported the observed decrease in iron concentration (Figure ).…”

“…A mutation in LOC_Os11g29850/ABCI8 was reported to cause albino leaves with defective chloroplasts under continuous cloudy/rainy weather (Zeng et al ). Our findings showed that light is the key factor affecting albinism of the tsc1 mutant after transplanting.…”