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.