We investigated the mechanism regulating cytoplasmic male sterility (CMS) in Brassica rapa ssp. pekinensis
using floral bud transcriptome analyses of Ogura-CMS Chinese cabbage and its maintainer line in B. rapa
300-K oligomeric probe (Br300K) microarrays. Ogura-CMS Chinese cabbage produced few and infertile
pollen grains on indehiscent anthers. Compared to the maintainer line, CMS plants had shorter filaments
and plant growth, and delayed flowering and pollen development. In microarray analysis, 4646 genes
showed different expression, depending on floral bud size, between Ogura-CMS and its maintainer line.
We found 108 and 62 genes specifically expressed in Ogura-CMS and its maintainer line, respectively.
Ogura-CMS line-specific genes included stress-related, redox-related, and B. rapa novel genes. In the
maintainer line, genes related to pollen coat and germination were specifically expressed in floral buds
longer than 3 mm, suggesting insufficient expression of these genes in Ogura-CMS is directly related
to dysfunctional pollen. In addition, many nuclear genes associated with auxin response, ATP synthesis,
pollen development and stress response had delayed expression in Ogura-CMS plants compared
to the maintainer line, which is consistent with the delay in growth and development of Ogura-CMS
plants. Delayed expression may reduce pollen grain production and/or cause sterility, implying that
mitochondrial, retrograde signaling delays nuclear gene expression.