Cloning and molecular characterization of a putative habanero pepper SERK1 cDNA expressed during somatic and zygotic embryogenesis

Background: Plant gene homologs that control cell differentiation can be used as biotechnological tools to study the in vitro cell proliferation competence of tissue culture-recalcitrant species such as peppers. It has been demonstrated that SERK1 homologs enhance embryogenic competence when overexpressed in transformed tissues; therefore, cloning of a pepper SERK1 homolog was performed to further evaluate its biotechnological potential. Results: A Capsicum chinense SERK full-length cDNA (CchSERK1) was cloned and characterized at the molecular level. Its deduced amino acid sequence exhibits high identity with sequences annotated as SERK1 and predicted-SERK2 homologs in the genomes of the Capsicum annuum CM-334 and Zunla-1 varieties, respectively, and with SERK1 homologs from members of the Solanaceae family. Transcription of CchSERK1 in plant tissues, measured by quantitative RT-PCR, was higher in stems, flowers, and roots but lower in leaves and floral primordia. During seed development, CchSERK1 was transcribed in all zygotic stages, with higher expression at 14 days post anthesis. During somatic embryogenesis, CchSERK1 was transcribed at all differentiation stages, with a high increment in the heart stage and lower levels at the torpedo/cotyledonal stages. Conclusion: DNA sequence alignments and gene expression patterns suggest that CchSERK1 is the C. chinense SERK1 homolog. Significant levels of CchSERK1 transcripts were found in tissues with cell differentiation activities such as vascular axes and during the development of zygotic and somatic embryos. These results suggest that CchSERK1 might have regulatory functions in cell differentiation and could be used as a biotechnological tool to study the recalcitrance of peppers to proliferate in vitro.

Cloning of the Coffea canephora SERK1 promoter and its molecular analysis during the cell-to-embryo transition

Background: Somatic embryogenesis receptor-like kinase 1 (SERK1) is a cell membrane receptor active in different plant tissues and involved in cell differentiation activities including somatic embryogenesis. The identification of promoter elements responsible for SERK1 expression during the onset of somatic embryogenesis can be useful to understand the molecular regulation of the cell-to embryo transition, and these promoter elements represent biotechnological tools in plant organ tissue culture. Results: A −1,620 bp DNA sequence located upstream of the Coffea canephora SERK1 gene homologue (CcSERK1) was isolated, and then, different segments containing key response elements (REs) for somatic embryogenesis onset and development were fused to the uidA (encoding a ß-glucuronidase, GUS) reporter gene to evaluate its expression in transgenic leaf explants. DNA segments of −1,620 and −1048 bp in length directed uidA expression with patterns in leaf explants similar to those occurring during somatic embryogenesis. When a −792-bp fragment was used, uidA expression disappeared only in leaf explants and pro-embryogenic mass but persisted in developing embryos. No uidA expression was detected in any embryogenic stage when a −618-bp fragment was used. Conclusion: DNA deletions showed that a −1048-bp sequence located upstream of the CcSERK1 gene is sufficient to direct gene expression during the onset and the development of C. canephora somatic embryogenesis. The DNA segment located between −1048 and −792 bp (containing BBM and WUS REs) is needed for gene expression before embryogenesis onset but not during embryo development. The promoter segment between −792 and −618 bp (including GATA, ARR1AT, and ANT REs) regulates gene expression in developing embryos.

Ectopic expression of the Coffea canephora SERK1 homolog-induced differential transcription of genes involved in auxin metabolism and in the developmental control of embryogenesis.

Somatic embryogenesis receptor-like kinase 1 (SERK1) is a membrane receptor that might serve as common co-regulator of plant cell differentiation processes by forming heterodimers with specific receptor-like kinases. The Coffea canephora SERK1 homolog (CcSERK1) was cloned in this work, and its early function in the transcription of embryogenesis master genes and of genes encoding proteins involved in auxin metabolism was investigated by externally manipulating its expression in embryogenic leaf explants, before the appearance of embryogenic structures. Overexpression of CcSERK1 early during embryogenesis caused an increase in the number of somatic embryos when the 55-day process was completed. Suppression of CcSERK1 expression by RNA interference almost abolished somatic embryogenesis. Real time-PCR experiments revealed that the transcription of the CcAGL15, CcWUS, CcBBM, CcPKL, CcYUC1, CcPIN1 and CcPIN4 homologs was modified in direct proportion to the expression of CcSERK1 and that only CcLEC1 was inversely affected by the expression levels of CcSERK1. The expression of the CcYUC4 homolog was induced to more than 80-fold under CcSERK1 overexpression conditions, but it was also induced when CcSERK1 expression was silenced. The level of CcTIR1 was not affected by CcSERK1 overexpression but was almost abolished during CcSERK1 silencing. These results suggest that CcSERK1 co-regulates the induction of somatic embryogenesis in Coffea canephora by early activation of YUC-dependent auxin biosynthesis, auxin transport mediated by PIN1 and PIN4, and probably auxin perception by the TIR1 receptor, leading to the induction of early-stage homeotic genes (CcAGL15, CcWUS, CcPKL and CcBBM) and repression of late-stage homeotic genes (CcLec1).

Systemic induction of a Capsicum chinense nitrate reductase by the infection with Phytophthora capsici and defence phytohormones.

The mRNA differential display technique was used to identify genes from Habanero pepper (Capsicum chinense Jacq.) seedlings whose expression is modified systemically by infection with the oomycete Phytophthora capsici L. Experiments with different oligonucleotide primer combinations revealed that no single gene was synthesised de novo. Instead, the quantitative accumulation of multiple transcripts was found. From these transcripts, levels of a nitrate reductase (Capsicum chinense nitrate reductase, CcNR), which has a high percentage of identity with other Solanaceae NRs, showed a consistent increase a few hours after inoculation (hai) with P. capsici. Reverse northern blotting revealed the existence of basal levels of CcNR transcripts in different adult tissues; however, systemic levels rose dramatically after spraying seedlings with salicylic acid (SA) and ethephon (ET) but not with methyl jasmonate (MeJa). Both P. capsici and defence phytohormones (DP) also modified NR enzymatic activity (nitrite:NAD(+) oxidoreductase; EC 1.7.1.1) with similar kinetics. Because the application of DP induced and activated the CcNR differentially, it is possible that the activity of CcNR is related to a specific host defence response.

Agrobacterium tumefaciens-transient genetic transformation of Habanero pepper (Capsicum chinense Jacq. ) leaf explants

Most of the pepper species of the genus Capsicum have been recalcitrant to efficient Agrobacterium tumefaciens-mediated stable or transient, genetic transformation. In the present work, we optimized a protocol for transient transformation of the Habanero pepper (Capsicum chinense Jacq.) through the standardization of several experimental factors. These included the age of the plants, the temperature, the length of co-cultivation, the application of a negative (vacuum) and/or a positive (infiltration) pressure, along with micro injection, the use of acetosyringone during the bacterial culturing, and modification of the pH during the GUS assay to eliminate the endogenous beta-glucuronidase activity. The standardized protocol, which yielded nearly 55 percent fully transformed leaf explants, was used to successfully mobilize two empty binary vectors (pCAMBIA2301 and pCAMex), as well as the C. chinense cDNAs encoding the pathogenesis-related protein 10 and esterase, respectively.

Identification of genes expressed as a result of lindane exposure in Oreochromis niloticus using differential display.

In order to assess the effect of lindane exposure on gene expression in tilapia (Oreochromis niloticus), twenty male fish were individually weighted and injected intraperitoneally with a single dose of lindane (19.09 mg/kg bw) using corn oil as a carrier vehicle, while a second group of twenty male fish (controls) was only injected with the carrier vehicle. Groups of four fish each were then sacrificed at 3, 6, 12, 18 and 24h after treatment application and total RNA was extracted from liver tissue. The differential display (DD) technique was then used to identify differentially expressed cDNA fragments between treatment and control fish. A total of fifty cDNA fragments were isolated and sequenced, from which only four showed homology with genes previously described in other fish species, namely the immunoglobulin heavy chain (IgH), coagulation factor V (FV), casein kinase 2 alpha (CK2a), and the receptor protein-tyrosine-like phosphatase (RPT-LP). The expression of such genes was confirmed using quantitative real time-polymerase chain reaction (QRT-PCR). Results showed that lindane exposure triggered the differential expression of these genes during the first 6, 18 and 24h subsequent to treatment application, suggesting that lindane exposure can trigger a rapid immune system response in tilapias.