Os10g0497300

This gene is the same as Rf1a,Rf-1,or Rf5, which are involved in fertility restoration.

Annotated Information

Introduction

This gene is called "Pollen fertility restoration-1", which encodes a pentatricopeptide repeat (PPR) protein[1], and we show that Rf5 is identical to Rf1 (Rf1a) in BT-CMS rice. It co-segregates with the SSR marker RM3150, and is flanked by RM1108 and RM5373, which are 0.9 cM and 1.3 cM away, respectively.[2].It is located on chromosome 10, 7.8 cM from the microsatellite marker RM258[3].

Function

RF5 plays a critical role in the assembly of the fertility restoration complex[1]. The cloning of fertility restorer genes for CMS from petunia, rapeseed, radish, sorghum, and rice has identified PPR proteins as essential components for fertility restoration. Apart from the PPR13 restorer of fertility in sorghum, which belongs to the E type, all other RF-related proteins belong to the P subclass of PPR proteins. Their structural simplicity suggests the need for additional interaction partners to direct transcript binding and cleavage. PPR4 and PPR2 from maize chloroplasts associate with RNase-sensitive high molecular mass complexes that coprecipitate with ribosomes[4-5]. In the same vein, Arabidopsis thaliana pTAC2 (for plastid transcriptionally active chromosome 2) was copurified with transcription complexes from chloroplasts. To date, very few direct protein partners of PPR proteins have been identified. The conventional model suggests that RF proteins process CMSassociated transcripts directly, owing to the RNA binding activity of PPR proteins. So far, the fertility restoration complex and its partner proteins have not been identified, and few results have shown direct interactions between the RF and CMS-associated transcripts. A Petunia RF restorer protein, PPR592, associates with a soluble, mitochondrial, RNase-sensitive, high molecular mass protein complex attached to the inner membrane. PPR-B has been demonstrated to associate with the orf138RNAin vivo by immunoprecipitation experiments. It remains unclear whether these interactions between the RNA and RF proteins are direct.In this study, we demonstrated that in mitochondria from the NILF1 hybrid, an RFC with a size of 400 to 500 kD functions in the restoration of fertility. These investigations provided evidence that RF5 is not involved in RNA binding and that RNA processing occurs via a GRP with RNA binding activity that is necessary for the restoration of pollen fertility. We postulate that the critical function of RF5 is to assemble the RFC in mitochondria, wherein Rf5 and GRP coordinate the processing of transcripts involved in fertility restoration in HL-CMS.

The cytoplasmic male sterility (CMS) phenotype in plants can be reversed by the action of nuclear-encoded fertility restorer (Rf) genes. The molecular mechanism involved in Rf gene–mediated processing of CMS-associated transcripts is unclear, as are the identities of other proteins that may be involved in the CMS–Rf interaction. In this study, we cloned the restorer gene Rf5 for Hong-Lian CMS in rice and studied its fertility restoration mechanism with respect to the processing of the CMS-associated transcript atp6-orfH79. RF5, a pentatricopeptide repeat (PPR) protein, was unable to bind to this CMS associated transcript; however, a partner protein of RF5 (GRP162, a Gly-rich protein encoding 162 amino acids) was identified to bind to atp6-orfH79. GRP162 was found to physically interact with RF5 and to bind to atp6-orfH79 via an RNA recognition motif. Furthermore, we found that RF5 and GRP162 are both components of a restoration of fertility complex (RFC) that is 400 to 500 kD in size and can cleave CMS-associated transcripts in vitro. Evidence that a PPR protein interacts directly with a Gly-rich protein to form a subunit of the RFC provides a new perspective on the molecular mechanisms underlying fertility restoration.

Location

Cytoplasmic male sterility (CMS), a maternally inherited inability to produce functional pollen, has been observed in more than 200 species of higher plants. At the molecular level, CMS is correlated with aberrant, often chimeric, mitochondrial genes in all cases that have been examined. The CMS phenotype can be rescued by a class of nuclear genes termed restorer of fertility (Rf) genes. In general, Rf genes belong to a large, well-defined family of genes that encode organelle-targeted pentatricopeptide repeat (PPR) proteins. The Honglian cytoplasmic male sterility (cms-HL) system, a novel type of gametophytic CMS in indicarice, is being used for the large-scale commercial production of hybrid rice in China. However, the genetic basis of fertility restoration (Rf) in cms-HL remains unknown. Previous studies have shown that fertility restoration is controlled by a single locus located on chromosome 10, close to the loci Rf1 and Rf4, which respond to cms-BT and cms-WA, respectively. To determine if the Rf locus for cms-HL is different from these Rf loci and to establish fine-scale genetic and physical maps for map-based cloning of the Rf gene, high-resolution mapping of the Rf gene was carried out using RAPD and microsatellite markers in three BCF1 populations. The results of the genetic linkage analysis indicated that two Rf loci respond to cms-HL, and that these are located in different regions of chromosome 10. One of these loci, Rf5 , co-segregates with the SSR marker RM3150, and is flanked by RM1108 and RM5373, which are 0.9 cM and 1.3 cM away, respectively. Another Rf locus, designated as Rf6(t), co-segregates with RM5373, and is flanked by RM6737 and SBD07 at genetic distances of 0.4 cM. The results also demonstrated these loci are distinct from Rf1 and Rf4. A 105-kb BAC clone covering the Rf6(t) locus was obtained from a rice BAC library. The sequence of a 66-kb segment spanning the Rf6(t) locus was determined by a BLASTX search in the genomic sequence database established for the cultivar 93-11.

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References

[1]Jun Hu, Kun Wang, Wenchao Huang, and et al.(2012) The Rice Pentatricopeptide Repeat Protein RF5 Restores Fertility in Hong-Lian Cytoplasmic Male-Sterile Lines via a Complex with the Glycine-Rich Protein GRP162. Plant Cell. 24(1): 109–122.

[2]Liu, X.Q., Xu, X., Tan, Y.P.,and et al.(2004)Inheritance and molecular mapping of two fertility-restoring loci for Honglian gametophytic cytoplasmic male sterility in rice (Oryza sativa L.). Mol. Genet. Genomics 271: 586–594.

[3]Huang QY, He YQ, Jing RC, and et al.(2000) Mapping of the nuclear fertility restorer gene for HL CMS in rice using microsatellite markers. Chinese Sci Bull 45:430–432.

[4]Williams, P.M., and Barkan, A. (2003). A chloroplast-localized PPR protein required for plastid ribosome accumulation. Plant J. 36:675–686.

[5]Schmitz-Linneweber, C., Williams-Carrier, R.E., Williams-Voelker, P.M.,and et al.(2006). A pentatricopeptide repeat protein facilitates the trans-splicing of the maize chloroplast rps12 pre-mRNA. Plant Cell 18: 2650–2663.