Isolation and characterization of three duplicated PISTILLATA genes in Brassica napus

BnC15 and BnATA20, the different putative components, control anther development in Brassica napus L

In Brassica napus, male fertility depends on proper cell differentiation in the anther. However, relatively little is known about the genes regulating anther cell differentiation and function. Here, we report two floral organ specific genes, BnC15 and BnATA20, derived from a B. napus two-line Rs1046A/B floral subtractive library. Although BnC15 and BnATA20 genes have a different expression pattern in anthers demonstrated by in situ hybridization and real-time PCR analysis, silencing of both genes in B. napus by antisense suppression resulted in pollen abortion after microspore release. Light and electron microscopy observation revealed the lack of plastoglobuli, lipid bodies and sporopollenin secreted from the tapetum leading to aberrations in exine sculpturing and the formation of a pollen coat. In addition, the microspores were squeezed to the irregular shape in the locule in the end. As shown by gene expression analysis in transgenic plants and the comparison of anther development between bnc15 or bnata20 mutants and Rs1046A, BnC15 and BnATA20 were positively regulated downstream of Rf gene controlling the fertility of Rs1046B in the same pathway. The results support the hypothesis that BnC15 and BnATA20 are crucial components of a genetic network that controls tapetum development and exine sculpturing.

Isolation and characterization of a novel BcMF14 gene from Brassica campestris ssp. chinensis

A putative RALF (rapid alkalinization factor)-like gene (GenBank accession number EF523517), named BcMF14, was isolated from Chinese cabbage (Brassica campestris L. ssp. chinensis Makino, syn. B. rapa ssp. chinensis) by rapid amplification of cDNA ends (RACE) based on a cDNA-AFLP differential fragment exclusively expressed in fertile line. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) discovered that BcMF14 was prominently expressed in stage four and five flower buds of fertile line, no expression in vegetative structures or in sterility line. Detailed RT-PCR illuminated its strong expression in stamens. Successful suppression of BcMF14 gene expression greatly reduced the normal pollen grains. The frequency of abnormal pollen grains was 48.95% in the mutant with many shriveled pollen grains with irregular shape and some larger ones with deep hollows along the germination ditch. Pollen germination was stopped because of the severely twisted pollen tubes. These results demonstrate a potential role of the BcMF14 gene in the development of male gametogenesis in Chinese cabbage.

Molecular analysis and expression of a floral organ-specific polygalacturonase gene isolated from rapeseed (Brassica napus L.)

High throughput screening of stage-specific differentially expressed genes in a Brassica napus two-line Rs1046A/B subtractive library was used to identify the BnQRT3 gene associated with cell wall metabolism. Phylogenetic analysis indicates the protein product of BnQRT3 is polygalacturonase. According to cytological comparisons of Rs1046 sterile and fertile anthers, RT-PCR studies and in situ hybridizations, BnQRT3 is expressed most strongly in floral organs and may play an essential role in pollen maturation. Analysis of the histological staining pattern of BnQRT3 promoter-GUS constructs in transgenic Arabidopsis and Brassica napus revealed that proximal part of 5'-flanking region directed expression in the vascular tissue of filaments, veins in sepal and petals, stigma, branch connective and the floral organ abscission zone during the open flower stage. In the meanwhile, Activity of BnQRT3 was detected in the anthers, which commences at the microsporocyte stage and persists as anther approaches dehiscence. Strong GUS expression also can be observed in the vascular tissue of leaves and stem by compression with forceps or excision, suggesting that the BnQRT3 promoter is responsive to wounding.