Upregulation of the AT-hook DNA binding gene BoMF2 in OguCMS anthers of Brassica oleracea suggests that it encodes a transcriptional regulatory factor for anther development

Abstract

Ogura cytoplasmic male sterility (OguCMS) is the most important CMS system used for F1 hybrid cabbage production worldwide. The anther abortion and defective pollen development exhibited in OguCMS are coordinately regulated by the mitochondrial male sterile gene orf138 and many nuclear transcriptional regulatory factors. AT-hook DNA binding proteins regulate cell-specific gene expression. In this study, we cloned the gene encoding the AT-hook DNA binding protein BoMF2 using the cDNA-AFLP TDF sequence, which was upregulated in OguCMS cabbage flower buds, as a querying probe. BoMF2 contains a 783-nt continuous complete open reading frame encoding a 260 amino-acid polypeptide. In vivo transient expression assays using GFP fusions showed that BoMF2 protein was located in the nucleus. BoMF2 was preferentially expressed in cabbage stamens, with a short expression window at anther development stage 7-8. However, in OguCMS flowers, BoMF2 expression continued into the mature pollen stage and was concomitant with the continued proliferation of tapetum cells exhibited in this mutant. Arabidopsis plants overexpressing BoMF2 showed significantly shorter siliques than the wild type, as well as decrease of pollen viability. These results suggest that BoMF2, a transcriptional regulatory factor, might regulate tapetum proliferation during anther development.