Abstract
BnAP2, an APETALA2 (AP2)-like gene, has been isolated from Brassica napus cultivar Zhongshuang 9. The cDNA of BnAP2, with 1, 299 bp in length, encoded a transcription factor comprising of 432 amino acid residues. Results from complementary experiment indicated that BnAP2 was completely capable of restoring the phenotype of Arabidopsis ap2-11 mutant. Together with the sequence and expression data, the complementation data suggested that BnAP2 encodes the ortholog of AtAP2. To address the transcriptional activation of BnAP2, we performed transactivation assays in yeast. Fusion protein of BnAP2 with GAL4 DNA binding domain strongly activated transcription in yeast, and the transactivating activity of BnAP2 was localized to the N-terminal 100 amino acids. To further study the function of BnAP2 involved in the phenotype of B. napus, we used a transgenic approach that involved targeted RNA interference (RNAi) repression induced by ihp-RNA. Floral various phenotype defectives and reduced female fertility were observed in B. napus BnAP2-RNAi lines. Loss of the function of BnAP2 gene also resulted in delayed sepal abscission and senescence with the ethylene-independent pathway. In the strong BnAP2-RNAi lines, seeds showed defects in shape, structure and development and larger size. Strong BnAP2-RNAi and wild-type seeds initially did not display a significant difference in morphology at 10 DAF, but the development of BnAP2-RNAi seeds was slower than that of wild type at 20 DAF, and further at 30 DAF, wild-type seeds were essentially at their final size, whereas BnAP2-RNAi seeds stopped growing and developing and gradually withered.
Highlights
Flower is the most important organ of a flowering plant
We studied the function of B. napus AP2 (BnAP2) using the transgenic approach that involved targeted RNA interference repression induced by ihp-RNA in B. napus, floral various phenotype defectives and reduced female fertility were observed in BnAP2-RNAi lines, loss of the function of BnAP2 gene resulted in delayed abscission and senescence of sepals, in the strong BnAP2-RNAi lines, seeds showed defects in shape, structure and development and larger size
Nine amino acid substitutions and sixteen amino acids deletions exist in the AP2 domains between BnAP2 and Brassica rapa AP2 (BrAP2) genes compared with other AP2-(like) genes, seven amino acids substitutions and 16 deletions of 25 full linker sequences of the predicted occurred (Fig. 1), while the amino acids mentioned above are conserved in the other AP2-(like) genes
Summary
Flower is the most important organ of a flowering plant. As a close relative of Arabidopsis thaliana, Brassica napus has a concentric arrangement of four types of flower organs: four sepals in whorl 1, four petals in whorl 2, six stamens in whorl 3, and two fused carpels in whorl 4. Floral organ identity is specified by the transcription factors encoded by 3 classes of floral homeotic genes: the A, B and C functional genes [1,2,3]. Class A genes specify sepals and interact with class B genes to specify petals. Class C genes specify carpels and interact with class B genes to specify stamens. Classes A and C genes act antagonistically to restrict each other’s activities in perianth and reproductive organs respectively
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