Molecular cloning and characterization of a novel pollen predominantly membrane protein gene BcMF12 from Brassica campestris ssp. chinensis

Whole-transcriptome analysis and construction of an anther development-related ceRNA network in Chinese cabbage (Brassica campestris L. ssp. pekinensis)

Anther development is precisely regulated by a complex gene network, which is of great significance to plant breeding. However, the molecular mechanism of anther development in Chinese cabbage is unclear. Here, we identified microRNAs (miRNAs), mRNAs, long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) related to anther development in Chinese cabbage (Brassica campestris L. ssp. pekinensis) to construct competitive endogenous RNA (ceRNA) regulatory networks and provide valuable knowledge on anther development. Using whole-transcriptome sequencing, 9055, 585, 1344, and 165 differentially expressed mRNAs (DEmRNAs), miRNAs (DEmiRNAs), lncRNAs (DElncRNAs), and circRNAs (DEcircRNAs) were identified, respectively, in the anthers of Chinese cabbage compared with those in samples of the vegetative mass of four true leaves. An anther-related ceRNA regulatory network was constructed using miRNA targeting relationships, and 450 pairs of ceRNA relationships, including 97 DEmiRNA-DEmRNA, 281 DEmiRNA-DElncRNA, and 23 DEmiRNA-DEcircRNA interactions, were obtained. We identified important genes and their interactions with lncRNAs, circRNAs, and miRNAs involved in microsporogenesis, tapetum and callose layer development, pollen wall formation, and anther dehiscence. We analyzed the promoter activity of six predominant anther expression genes, which were expressed specifically in the anthers of Arabidopsis thaliana, indicating that they may play an important role in anther development of Chinese cabbage. This study lays the foundation for further research on the molecular mechanisms of anther growth and development in Chinese cabbage.

BcMF11, a novel non-coding RNA gene from Brassica campestris, is required for pollen development and male fertility

KEY MESSAGE : BcMF11 as a non-coding RNA gene has an essential role in pollen development, and might be useful for regulating the pollen fertility of crops by antisense RNA technology. We previously identified a 828-bp full-length cDNA of BcMF11, a novel pollen-specific non-coding mRNA-like gene from Chinese cabbage (Brassica campestris L. ssp. chinensis Makino). However, little information is known about the function of BcMF11 in pollen development. To investigate its exact biological roles in pollen development, the BcMF11 cDNA was antisense inhibited in transgenic Chinese cabbage under the control of a tapetum-specific promoter BcA9 and a constitutive promoter CaMV 35S. Antisense RNA transgenic plants displayed decreasing expression of BcMF11 and showed distinct morphological defects. Pollen germination test in vitro and in vivo of the transgenic plants suggested that inhibition of BcMF11 decreased pollen germination efficiency and delayed the pollen tubes' extension in the style. Under scanning electron microscopy, many shrunken and collapsed pollen grains were detected in the antisense BcMF11 transgenic Chinese cabbage. Further cytological observation revealed abnormal pollen development process in transgenic plants, including delayed degradation of tapetum, asynchronous separation of microspore, and aborted development of pollen grain. These results suggest that BcMF11, as a non-coding RNA, plays an essential role in pollen development and male fertility.

cDNA-AFLP analysis on bolting or flowering of flowering Chinese cabbage and molecular characteristics of BrcuDFR-like/BrcuAXS gene

The molecular basis of flower bud differentiation in flowering Chinese cabbage (Brassica rapa L. ssp. Chinensis var. utilis Tsen et Lee) was studied in this work. Samples were taken from two varieties, the early-blooming "Youqin 49" and the late-blooming "Youqingtiancaixin 80", at five different developmental stages and studied via cDNA-AFLP. Nineteen expression sequence tags (ESTs) associated with bolting or flowering were isolated and cloned. Blast results indicated that 15 ESTs were involved in the synthesis of anthocayanins, photosynthesis, signal transduction, and phytochrome production. Two ESTs had high similarity to hypothetical proteins with unknown function. Two other ESTs shared no similarity to any sequence in the NCBI database and potentially may be newly identified genes. The deduced amino acid sequences of EST amplified by primer A6T4 or A8T4 had high similarity to both dihydroflavonol reductase (DFR) and UDP-D: -apiose/UDP-D: -xylose synthase (AXS), thus was named BrcuDFR-like/BrcuAXS. Using the cDNA sequence, a putative BrcuDFR-like/BrcuAXS gene was cloned and characterized from flowering Chinese cabbage via rapid amplification of cDNA ends (RACE). The full-length cDNA has 1332 bp with an open frame of 919 bp which codes for a polypeptide of 313 amino acids. The corresponding genome sequence is 2,046 bp. Comparison of cDNA and its corresponding genomic sequence indicates that BrcuDFR-like/BrcuAXS contains 9 exons and 8 introns. The temporal expression patterns indicated the gene is more likely to encode the DFR protein, which catalyzes the synthesis of anthocayanins, than UDP-D: -apiose/UDP-D: -xylose synthase (AXS), which catalyzes the conversion of UDP-D: -glucuronate to a mixture of UDP-D: -apiose and UDP-D: -xylose. Further work is needed to determine what role BrcuDFR-like/BrcuAXS plays during floral organ development.

Sequence characterization and expression pattern of BcMF21, a novel gene related to pollen development in Brassica campestris ssp. chinensis

In this report a full length cDNA, Brassica campestris Male Fertile 21 (BcMF21) was successfully isolated from one of the cDNA-amplified fragment length polymorphism (cDNA-AFLP) transcript-derived fragments (TDFs), BBP10, that was found down-regulated in the flower buds of sterile plants in Brassica campestris L. ssp. chinensis Makino genic male sterile (GMS) AB line system (Bcajh 97-01A/B). BcMF21 protein structure analysis showed a signal peptide at the N-terminus; two protein kinase C phosphorylation sites, five N-myristoylation sites and one casein kinase II phosphorylation site. The promoter region of BcMF21, a 779 bp upstream of ATG was isolated by thermal asymmetric interlaced-PCR (TAIL-PCR). Bioinformatics analysis revealed that the promoter of BcMF21 contained several classical cis-acting elements and three pollen specific elements. Transient expression analysis showed that the promoter could drive green fluorescence protein (GFP) expression. Quantitative reverse transcript-PCR analysis revealed that BcMF21 was specifically expressed in flower buds. The transcript level of BcMF21 was much lower in the sterile flower buds than in the fertile flower buds in 'Bcajh 97-01A/B' system. In situ hybridization further showed that BcMF21 was only expressed in the tetrads and the microspores at the tetrad stage and the uninucleate stage. In addition, phylogenetic analysis demonstrated that the BcMF21 was relative conserved within family Crucifereae and might be originated from the ancestor diploid B. campestris within genus Brassica according to the Triangle of U theory.

Functional analysis of a rice late pollen-abundant UDP-glucose pyrophosphorylase (OsUgp2) promoter

OsUgp2, a rice UDP-glucose pyrophosphorylase gene, has previously been shown to preferentially express in maturing pollens and plays an important role in pollen starch accumulation. Here, a 1943 bp promoter fragment (P1943) of OsUgp2 was characterized by 5' deletion and gain-of-function experiments. P1943 and its 5' deletion derivatives (P1495, P1005, P665 and P159) were fused to GUS reporter gene and stably introduced into rice plants. Histochemical analyses of different tissues and pollens at different developmental stages of the transgenic plants showed that P1943 could only direct GUS expression in binucleate pollens. P1495 and P1005 could still drive GUS expression in binucleate pollens but at a lower level. On the other hand, neither P665 nor P159 transformant exhibited any GUS activity in pollens. Gain-of-function analyses showed that the region (-1005 to -665 relative to translation start site) combined with a minimal CaMV 35S promoter could direct GUS expression in pollens. Further analysis of 5' deletion truncated at -952, -847 and -740 delimited a 53 bp region (-1005 to -952) essential for pollen-specific expression. The 53 bp sequence contains two motifs of TTTCT and TTTC, which were known to be pollen-specific cis-elements. In addition, the same P1943-GUS fusion construct was introduced into tobacco to analyze its specificity in dicotyledon. Interestingly, the GUS expression pattern in transgenic tobacco was quite different from that in rice. High level of GUS expression was detected in mature pollens as well as leaves, roots, sepals and stigmas. These findings suggested a complicated transcriptional regulation of OsUgp2.

Characterization of a new male sterility-related gene Camf1 in Capsicum annum L

For the sake of screening novel genes related to the male sterility in chili pepper for studying the molecular mechanism of plant male sterility, the gene differential expression analysis was performed by cDNA-amplified fragment length polymorphism (cDNA-AFLP) in the genic male sterile-fertile line 114AB of Capsicum annum L., and a variety of differentially expressed cDNA fragments were detected in fertile or sterility material. Camf1, a transcript-derived fragment (TDF) accumulated in fertile line flower buds was further investigated. The Camf1 has 1,854 bp in length with no introns containing a 1,707-bp open reading frame (ORF). The deduced amino acid sequence of Camf1 shares higher similarity to some members from a glyoxal oxidase-related protein family, and has a glyoxal oxidase conserved domain at the N-terminus and a domain of unknown function (DUF1929) at C-terminal end. Expression analysis showed that Camf1 expressed only in stage 3-7 flower buds of male fertile of C. annum L. 114AB, and no detection in all organs of male sterility. The peak of expression level of Camf1 appeared at stage 4 flower buds of fertile line. Furthermore, expression analysis of different organs revealed that Camf1 expressed only in anthers of male fertile material and there were no expression in sepals, petals, pistils, roots, stems, leaves and open flowers. These results suggested that Camf1 was an anther-specific gene and might be essential for the fertility of C. annum L.

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.