Abstract
Flowering occurs in angiosperms during a major developmental transition from vegetative growth to the reproductive phase. Squamosa promoter binding protein (SBP)-box genes have been found to play critical roles in regulating flower and fruit development, but their roles in grapevine have remained unclear. To better understand the functions of the grape SBP-box genes in both vegetative and reproductive growth phases, a full-length complementary DNA (cDNA) sequence of the putative SBP-box transcription factor gene, VpSBP11, was obtained from Chinese wild grapevine Vitis pseudoreticulata Wen Tsai Wang (W. T. Wang) clone ‘Baihe-35-1’. VpSBP11 encoded a putative polypeptide of 170 amino acids with a highly conserved SBP-domain with two zinc-binding sites of the Cx2C-x3-H-x11-C-x6-H (C2HCH) type and a nuclear localization signal. We confirmed that the VpSBP11 protein was targeted to the nucleus and possessed transcriptional activation activity by subcellular localization and trans-activation assay. Over-expression of VpSBP11 in Arabidopsis thaliana was shown to activate the FUL gene, and subsequently the AP1 and LFY genes, all of which were floral meristem identity genes, and to cause earlier flowering than in wild type (WT) plants. The pattern of vegetative growth was also different between the transgenic and WT plants. For example, in the VpSBP11 over-expressing transgenic plants, the number of rosette leaves was less than that of WT; the petiole was significantly elongated; and the rosette and cauline leaves curled upwards or downwards. These results were consistent with VpSBP11 acting as a transcription factor during the transition from the vegetative stage to the reproductive stage.
Highlights
Flowering occurs in angiosperms during a major developmental transition from vegetative growth to the reproductive phase [1]
The formation of normal flowers requires the signals of flowering which are integrated by floral integrator genes such as SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), FLOWERING LOCUS T (FT) and FLOWERING LOCUS D (FD) [5,6,7,8], and the expression of the flower-meristem-identity genes including FRUITFULL (FUL), APETALA1 (AP1), LEAFY (LFY), Squamosa, and so on [9,10,11,12]
Squamosa promoter binding proteins (SBP)-box genes were first discovered in Antirrhinum majus and two genes named AmSBP1 and -2 were identified based on their ability to interact with the promoter sequence region of the floral meristem identity gene Squamosa [15]
Summary
Flowering occurs in angiosperms during a major developmental transition from vegetative growth to the reproductive phase [1]. We reasoned that the precocious meristem identity transition in 35S: VvSBP11 could be due to upregulation of genes that were upstream regulators of floral meristem identity (LFY, FUL and AP1) To test this possibility, we examined their expression in the transgenic lines (SBP11-31, SBP11-35, SBP11-36) and in WT plants before and after the onset of the reproductive stage (5, 9, 11, 13 and 15 days after germination) by using quantitative real-time PCR (qRT-PCR) analysis. Compared to the other two genes, LFY was not as obviously up-regulated; its expression was greater in the transgenic lines than in WT: >10, >160-fold and >7-fold higher in SBP11-31, SBP11-35, and SBP11-36, respectively (Figure 4). ThlreeaprveredesselionnfteasttihvveeisbuVlaapldSlyeBPpin1e1dtiioctlareat;en(Estgh)eePneliectinogllietnhleeson. fgTtthhhseeorfereprdorseeslteitnneetlsaetaivvvieessubaollfalydtheeinpgdeeitncioaotltey;p(tehEse)ilPlluestnitgoratlhetedleonifngt(hhAes) of rosr(ee2pt1tredelsaeeyansvt,aentsivo=ef5tb0hleafodgreeenpaoectthyiopgleees;n(oiEltly)upsPteer,tai*toeplde
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