Ly. Wen et Cd. Chase, Mitochondrial gene expression in developing male gametophytes of male-fertile and S male-sterile maize, SEX PLANT R, 11(6), 1999, pp. 323-330
Mitochondria play a critical role in the normal development of the plant ma
le gametophyte and in the disruption of normal gametophyte development asso
ciated with cytoplasmically inherited male sterility (CMS). To investigate
the role of mitochondria in these processes, the accumulation of mitochondr
ial gene transcripts and the accumulation of nuclear gene transcripts encod
ing mitochondrial proteins were investigated through male gametophyte devel
opment in normal maize and through the course of pollen abortion in CMS-S m
aize. Male gametophytes differing in developmental stage were isolated from
male-fertile or male-sterile plants by sucrose density gradient centrifuga
tion. Mature pollen was collected from dehiscent anthers of male-fertile pl
ants. Aborted pollen, which collapsed during starch accumulation, was isola
ted from emergent tassels of CMS-S male-sterile plants. Microspores, develo
ping pollen and mature pollen exhibited striking differences in mitochondri
al transcript accumulation. Mature pollen lacked detectable mitochondrial t
ranscripts. Aborted pollen of CMS-S plants contained abundant, intact trans
cripts of all mitochondrial genes studied, but prematurely degraded transcr
ipts of several nuclear genes. Transcripts of the CMS-S associated mitochon
drial open reading frames (orf355 and orf77) were detected from the early s
tages of microspore development through the aborted pollen stage. The impli
cations of these findings are discussed in terms of the mitochondrial requi
rements for pollen function and the mechanism of pollen abortion in CMS-S m
aize.