RecQ helicases function in development, DNA repair, and gene targeting in Physcomitrella patens

RecQ DNA helicases are genome surveillance proteins found in all kingdoms of life. They are characterized best in humans, as mutations in RecQ genes lead to developmental abnormalities and diseases. To better understand RecQ functions in plants we concentrated on Arabidopsis thaliana and Physcomitrella patens, the model species predominantly used for studies on DNA repair and gene targeting. Phylogenetic analysis of the six P. patens RecQ genes revealed their orthologs in humans and plants. Because Arabidopsis and P. patens differ in their RecQ4 and RecQ6 genes, reporter and deletion moss mutants were generated and gene functions studied in reciprocal cross-species and cross-kingdom approaches. Both proteins can be found in meristematic moss tissues, although at low levels and with distinct expression patterns. PpRecQ4 is involved in embryogenesis and in subsequent development as demonstrated by sterility of ΔPpRecQ4 mutants and by morphological aberrations. Additionally, ΔPpRecQ4 displays an increased sensitivity to DNA damages and an increased rate of gene targeting. Therefore, we conclude that PpRecQ4 acts as a repressor of recombination. In contrast, PpRecQ6 is not obviously important for moss development or DNA repair but does function as a potent enhancer of gene targeting

HIMyb3, a putative regulatory factor in hop (Humulus lupulus L.), shows diverse biological effects in heterologous transgenotes

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Cloning and molecular analyses of hop transcription factors

Expression of hop chs_H1 and other hop chalcone synthase (CHS)-like enzymes was assayed in developing pollen tissue. Both, chs_H1 and valerophenone synthase (vps) are highly expressed in pollen suggesting the existence of common specific regulatory element(s). While vps is highly specific for female and male floral organs, the oligofamily of chs_H1 is expressed in both generative and somatic tissues, suggesting a more universal promoter. To identify novel transcription factors involved in the regulation of chs_H1 genes in lupulin glands, cone-specific ESTs showing homology to bZIP and bHLH were utilized to screen hop cDNA and genomic libraries. Additionally, inverse PCR was used to amplify full length cDNAs of members of two bZIP oligofamilies from hop. Transcription factors H/bZIP1A and H/bZIP2 have predicted molecular masses of 27.4 and 34.2 kDa, respectively. While H/bZIP1A is rather neutral (pI 6.42), H/bZIP2 is strongly basic (pI 8.51). A truncated variant of H/bZIP1 (H/bZIP1B) that is strongly basic but lacks the zipper domain was also cloned from hop. Additionally, the first bHLH transcription factor was cloned from hop. H/bHLH1 is a protein of 33.6 kDa with a predicted pI of 6.08. Based on semiquantitative RT PCR results, this TF is expressed specifically in hop floral and cone tissue. The combinatorial action of H/bZIP2 and other hop TFs that have been cloned, especially H/Myb1 and 3 were analyzed in P. hybrida and N. benthamiana transient expression systems. TF H/bZIP2, as well as both Myb TFs, were found as activators of chs_H1 promoter. In the combinatorial system, H/bZIP2 was found to modulate expression of H/Myb1 and H/Myb3 Trs from hop