Abstract

Cytoplasmic male sterility (CMS) in pepper (Capsicum annuum L.) has been associated with novel genes in the mitochondria, such as orf507 and Ψatp6-2. Plant sterility has been proved to result from the rearrangement of the mitochondrial genome. Previous studies have demonstrated that orf507 is co-transcribed with the cox II gene, and Ψatp6-2 is truncated at the 3′ region of the atp6-2 that is found in the maintainer line. Until this time, little has been known about the relationship between the novel gene and the function of its corresponding enzyme in mitochondria from the CMS pepper line. Moreover, the aberrant function of the mitochondrial enzymes is seldom reported in pepper. In this study, we observed that anther abortion occurred after the tetrad stage in the CMS line (HW203A), which was accompanied by premature programmed cell death (PCD) in the tapetum. The spatiotemporal expression patterns of orf507 and Ψatp6-2 were analyzed together with the corresponding enzyme activities to investigate the interactions of the genes and mitochondrial enzymes. The two genes were both highly expressed in the anther. The orf507 was down-regulated in HW203A (CMS line), with nearly no expression in HW203B (the maintainer line). In contrast, the cytochrome c oxidase activity in HW203A showed the opposite trend, reaching its highest peak at the tetrad stage when compared with HW203B at the same stage. The Ψatp6-2 in the CMS line was also down-regulated, but it was up-regulated in the maintainer line. The corresponding F1Fo-ATPase activity in the CMS line was gradually decreased along with the development of the anther, which showed the same trend for Ψatp6-2 gene expression. On the contrary, with up-regulated gene expression of atp6-2 in the maintainer line, the F1Fo-ATPase activity sharply decreased after the initial development stage, but gradually increased following the tetrad stage, which was contrary to what happened in the CMS line. Taken together, all these results may provide evidence for the involvement of aberrant mitochondrial cytochrome c oxidase and F1Fo-ATPase in CMS pepper anther abortion. Moreover, the novel orf507 and Ψatp6-2 genes in the mitochondria may be involved in the dysfunction of the cytochrome c oxidase and F1Fo-ATPase, respectively, which are responsible for the abortion of anthers in the CMS line.

Highlights

  • Cytoplasmic male sterility (CMS) is an important crop trait that is widely used in hybrid breeding to produce non-functional pollen [1]

  • We focused on investigating the relationship between novel mitochondrial orf507, Ψatp6-2gene and mitochondrial cytochrome c oxidase and F1Fo-ATP synthase enzyme in the oxidative phosphorylation complex (OPC)

  • To study the relationship of premature programmed cell death (PCD) on the abortion of pollen in HW203A, we compared the characteristics of pollen development with those from the HW203B

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Summary

Introduction

Cytoplasmic male sterility (CMS) is an important crop trait that is widely used in hybrid breeding to produce non-functional pollen [1]. The FAd subunit of mitochondrial F1Fo-ATP synthase in Arabidopsis thaliana, which is encoded by the MGP1 gene, is essential for anther development [25]. The orf522, homology to atp, encodes a subunit of F1Fo-ATP synthase and induces male sterility in the plant [32]. The two novel genes of interest have been widely used as selection markers in pepper production, and orf456 has been shown to induce male sterility in Arabidopsis thaliana, but the definite function of the genes and the relationship of the novel gene and its corresponding mitochondrial enzyme activity are not clear. We focused on investigating the relationship between novel mitochondrial orf507, Ψatp6-2gene and mitochondrial cytochrome c oxidase and F1Fo-ATP synthase enzyme in the OPC system of a CMS line, respectively.

Confirmation of Pollen Phenotype in the Sterile and Maintainer Lines
Gene Expression Analysis of Cox II-orf507 and Ψatp6-2
Evaluation of Cytochrome c Oxidase and ATPase Activity
Plant Materials and Growing Conditions
Analysis of Pollen Development
Extraction of Mitochondria
Gene Expression Pattern Analysis
ATPase and Cytochrome c Oxidase Activity
Conclusions

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