Antisense inhibition of mitochondrial pyruvate dehydrogenase E1α subunit in anther tapetum causes male sterility

Abstract

These two authors contributed equally to this work. SummaryWe hypothesized that cytoplasmic male sterility (CMS) in sugar beet may be the consequence of mitochondrial dysfunctions affecting normal anther development. To test the hypothesis, we attempted to mimic the sugar beet CMS phenotype by inhibiting the expression of mitochondrial pyruvate dehydrogenase (PDH), which is essential for the operation of the tricarboxylic acid (TCA) cycle. Screening with a cDNA library of sugar beet¯ower buds allowed the identi®cation of two PDH E1a subunit genes (bvPDH_E1a-1 and bvPDH_E1a-2). bvPDH_E1a-1 was found to be highly expressed in tap roots, whereas bvPDH_E1a-2 was expressed most abundantly in¯ower buds. Green¯uorescent protein (GFP) fusion of bvPDH_E1a revealed mitochondrial targeting properties. A 300-bp bvPDH_E1a-1 cDNA sequence (from 620 to 926) was connected to a tapetum-speci®c promoter in the antisense orientation and then introduced into tobacco. Antisense expression of bvPDH_E1a-1 resulted in conspicuously decreased endogenous bvPDH_E1a-1 transcripts and male sterility. The tapetum in the male-sterile anthers showed swelling or abnormal vacuolation. It is also worth noting that in the sterile anthers, cell organelles, such as elaioplasts, tapetosomes and orbicules were poorly formed and microspores exhibited aberrant exine development. These features are shared by sugar beet CMS. The results thus clearly indicate that inhibition of PDH activity in anther tapetum is suf®cient to cause male sterility, a phenocopy of the sugar beet CMS.

Interactions of Mitochondrial and Nuclear Genes That Affect Male Gametophyte Development

“…At this stage in development, demand for energy or particular mitochondrial biosynthetic products may be especially high, so that impairment of mitochondrial function becomes devastating. Consistent with this hypothesis is the finding that antisense downregulation of alternative oxidase orpyruvate dehydrogenase in the tobacco tapetum resulted in microspore death (Yui et al, 2003). Furthermore, although N. sylvestris plants that contain a deletion in a gene that encodes a mitochondrial NADH dehydrogenase subunit survive, they are male sterile (Gutierres et al, 1997).…”

The Cell Death in CMS Plants

“…Consistent with this, tobacco cells lacking AOX or cyanide-resistant respiration increased PCD in response to H 2 O 2 [48]. Furthermore, the downregulation of AOX or pyruvate dehydrogenase in the tobacco tapetum results in microspore death [49]. Ethylene signaling genes are preferentially expressed in rice tapetal cells, especially during the tetrad and unicellular stages [24], which suggest that ROS may firstly accumulate in tapetal cells, and trigger PCD in CMS anthers.…”

CsPDC-E1α, a novel pyruvate dehydrogenase complex E1α subunit gene from Camellia sinensis, is induced during cadmium inhibiting pollen tube growth

“…Previous studies have noted that the expression of plant mtPDC was high in anther (Thelen et al 1999;Luethy et al 2001). Furthermore, antisense inhibition of PDC-E1α subunit in anther tapetum causes male sterility (Yui et al 2003). In addition, Thelen et al (1999) reported that one E1α subunit and three E1β subunits were isolated from maize and their expression levels were the highest in pollen.…”