Mitochondrial gene expression in developing male gametophytes of male-fertile and S male-sterile maize

Abstract

Mitochondria play a critical role in the normal development of the plant male gametophyte and in the disruption of normal gametophyte development associated with cytoplasmically inherited male sterility (CMS). To investigate the role of mitochondria in these processes, the accumulation of mitochondrial gene transcripts and the accumulation of nuclear gene transcripts encoding mitochondrial proteins were investigated through male gametophyte development in normal maize and through the course of pollen abortion in CMS-S maize. Male gametophytes differing in developmental stage were isolated from male-fertile or male-sterile plants by sucrose density gradient centrifugation. Mature pollen was collected from dehiscent anthers of male-fertile plants. Aborted pollen, which collapsed during starch accumulation, was isolated from emergent tassels of CMS-S malesterile plants. Microspores, developing pollen and mature pollen exhibited striking differences in mitochondrial transcript accumulation. Mature pollen lacked detectable mitochondrial transcripts. Aborted pollen of CMS-S plants contained abundant, intact transcripts of all mitochondrial genes studied, but prematurely degraded transcripts of several nuclear genes. Transcripts of the CMS-S associated mitochondrial open reading frames (orf355 and orf77) were detected from the early stages of microspore development through the aborted pollen stage. The implications of these findings are discussed in terms of the mitochondrial requirements for pollen function and the mechanism of pollen abortion in CMS-S maize.

Interactions of Mitochondrial and Nuclear Genes That Affect Male Gametophyte Development

“…This model is consistent with the finding of several highly similar PPR motifcontaining genes at the nuclear loci in petunia, Brassica, and rice that have been found to affect the expression of CMS-associated orfs (Bentolila et al, 2002;Desloire et al, 2003;Kazama and Toriyama, 2003). It also is consistent with the finding that alleles of restorers in Brassica affect the expression of genuine mitochondrial genes and that the presence of the maize Rf3 locus affects transcripts of a chimeric region as well as known mitochondrial genes (Brown, 1999;Wen and Chase, 1999b).…”

Functional Conservation of MIKC*-Type MADS Box Genes in Arabidopsis and Rice Pollen Maturation

“…Starch can serve as an energy resource for subsequent germination, and starch levels hence can be considered as a checkpoint for pollen maturity (Datta et al, 2002). The degree of starch accumulation below a certain threshold can result in premature termination of pollen development and failure of pollen to complete second mitosis (Wen and Chase, 1999;Zhang et al, 2001;Datta et al, 2002;Han et al, 2006). Accordingly, the fact that pollen development of MADS68i/mads63 and MADS62i/mads63 plants is delayed and eventually arrested at the bicellular pollen stage while MADS68 single RNAi can finish the second mitosis to produce three nuclei is assumed to be related to the apparently different degrees of starch deficiency, which are much more severe in the double loss-of-function plants than in MADS68 single RNAi lines (Figures 4 and 5;see Supplemental Figure 8 online).…”

AOX1c, a novel rice gene for alternative oxidase; Comparison with rice AOX1a and AOX1b.

“…Expression of the AOX genes is upregulated under environmental stresses such as lower temperature (Stewart et al, 1990;Vanlerberghe and McIntosh, 1992;Ito et al, 1997) and wounding (Hiser and McIntosh, 1990). On the other hand, increases in AOX mRNA or protein have been detected during pollen development in maize (Wen and Chase, 1999), rice (Abe et al, 1997) and common bean (Johns et al, 1993). The detailed functions of the alternative pathway or AOX remain unclear.…”