A male sterility‐associated mitochondrial protein in wild beets causes pollen disruption in transgenic plants

Abstract

SummaryIn higher plants, male reproductive (pollen) development is known to be disrupted in a class of mitochondrial mutants termed cytoplasmic male sterility (CMS) mutants. Despite the increase in knowledge regarding CMSencoding genes and their expression, definitive evidence that CMS-associated proteins actually cause pollen disruption is not yet available in most cases. Here we compare the translation products of mitochondria between the normal fertile cytoplasm and the male-sterile I-12CMS(3) cytoplasm derived from wild beets. The results show a unique 12 kDa polypeptide that is present in the I-12CMS(3) mitochondria but is not detectable among the translation products of normal mitochondria. We also found that a mitochondrial open reading frame (named orf129) was uniquely transcribed in I-12CMS(3) and is large enough to encode the novel 12 kDa polypeptide. Antibodies against a GST-ORF129 fusion protein were raised to establish that this 12 kDa polypeptide is the product of orf129. ORF129 was shown to accumulate in flower mitochondria as well as in root and leaf mitochondria. As for the CMS-associated protein (PCF protein) in petunia, ORF129 is primarily present in the matrix and is loosely associated with the inner mitochondrial membrane. The orf129 sequence was fused to a mitochondrial targeting pre-sequence, placed under the control of the Arabidopsis apetala3 promoter, and introduced into the tobacco nuclear genome. Transgenic expression of ORF129 resulted in male sterility, which provides clear supporting evidence that ORF129 is responsible for the male-sterile phenotype in sugar beet with wild beet cytoplasm.

Mitochondrial-targeted Expression of orf456 Causes Male Sterility in Chinese Cabbage (Brassica rapa L.)

“…Several transformants containing orf gene constructs, with or without a mitochondrial targeting sequence, exhibited a semi-sterile or male sterile phenotype (He et al 1996;Wang et al 2006;Kim et al 2007;Yamamoto et al 2008). The failure of mitochondrial expression of novel orfs to induce male sterility is probably due to problems in disruption of mitochondrial membranes (Rhoads et al 1995;He et al 1996), effect on ATP synthase function (Bergman et al 2000;Sabar et al 2003) and pollen abortion by programmed cell death in transgenic plants.…”

“…It is generally considered that CMS is caused by the rearrangement of mitochondrial genomes, which, in many cases, is attributed to the generation of novel Open Reading Frames (ORF) (Yang and Zhang 2007). In a number of cases, transcripts originating from these altered open reading frames are translated into unique proteins that appear to interfere with mitochondrial function and pollen development (Yamamoto 2008). CMS anther degeneration is probably caused by dysfunction of tapetum or vacuolation of tapetum, PMCs, and microspores (Shi et al 2010).…”

The Cell Death in CMS Plants

“…After introducing the BT-rice orf79 gene into Taichung 65 carrying normal cytoplasm, it is revealed that ORF79 is toxic to plant regeneration when expresses as a fusion with mitochondrial targeting sequence of the ATPase subunit [11]. The CMS-associated mitochondrial protein in petunia, ORF129 results in male sterility in transgenic tobacco plants [12]. It is reported that the expression of sunflower cytoplasmic male sterilityassociated open reading frame, orfH522 induces male sterility in transgenic tobacco plants [13].…”

Plant Mitochondrial Genome Evolution and Cytoplasmic Male Sterility

“…However, as is the case with rice COX11 and other CMS systems, the mode of action may affect more than one category. An additional interesting dimension is that while the expression of CMS genes does not appear to be restricted to the male reproductive tissues in many species (Warmke and Lee, 1978;Abad et al, 1995;Yamamoto et al, 2008;Chen and Liu, 2014), accumulation of CMS-related proteins can be highly spatiotemporally specific to induce CMS (Abad et al, 1995;Wang et al, 2006;Luo et al, 2013).…”