-1- Plant genomes - •Chloroplast genome = circular, double strand...

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-1- Plant genomes

There are 3 types of genomes in plant cells:

•Chloroplast genome = circular, double stranded DNA that ranges from 120 to 160 kb in size and contains about 120-140 genes. If there are inverted repeats it is type II chloroplast genome.•Mitochondrial genome = 200 – 2500 kb and thus much larger than mammals. Lots of non- coding DNA, few genes. Promiscuous DNA = chloroplast DNA in mitochondrial DNA •Nuclear genome = DNA/chromosomes in cell Nucleus DNA -> histones -> nucleosomes(DNA 150bp wrapped around histones, cores H2A, H2B, H3 and H4) -> 30nm fibre -> wrapped into chromosomes microRNA = short (21-24 nucleotides) RNAs that are found in the genome regions that are not associated with protein-coding genes. They are generally well conserved among plant species.First a hairpin needs to be synthetized from the miRNA. These are produced by RNA polymerase II, like normal RNA. Dicer, a RNAse III endonucleoase, splices the duplex into mature miRNA which is also referred to as RNA induced silencing complex (RISC). Not shown in picture, RISC also has an Argonaut molecule (AGO1) attached.In translation of a gene, transcription factors (TFIID) bind to the TATA-box. These transcription factors then attract RNA- polymerase II and the gene is activated.Ribosomes attach to the 5’ side of the mRNA and move one codon in the 3’ direction.

Gene expression can be influenced by:

•Chromatin conformation (eu- and heterochromatin, open and closed), also including DNA methylation •Gene transcription (promotor, cis-elements = sequence elements that function to recruit the proteins that regulate transcription of a gene located on the same DNA-strand as the coding region for the gene, transcription factors) •RNA modification (splicing, alternative splicing = combining exons in different ways) •Translation •Post translational modification (phosphorylation, glycosylation and acetylation) •Localization (protein needs to be transported to compatible location) •Protein turnover Essential are promotor cis elements and a poly A signal.Alternative splicing = combining exons differently to obtain different proteins from the same gene.Promotor analysis = determining how long the upstream promotor sequence is by testing various promotor gene fusions. The moment that the gene product is not produced anymore determines how long the promotor fragment is. 3 / 4

promotor examples:

•Light regulated gene expression using light-responsive elements (LREs) •Abscisic acid-induced gene expression ABA •Tissue specific expression -2- Plant tissue culture Plant cells are totipotent = each individual plant cell can under right circumstances develop into a full plant.

Plant hormones:

1-Auxin => promotes cell division 2-Cytokinin => promotes cell division 3-Gibberellin => cell elongation, germination 4-Abscisic acid (ABA) => inhibits cell division 5-Ethylene =>

ripening Auxin:

•Natural: IAA

•Synthetic: IBA, NAA, 2,4-D (most commonly used because very

stable) cytokinin:

•natural: Zeatin, 2iP ((N

6 -(2-isopentyl)adenine)

•synthetic: kinetin, BAP (6-benzylaminopurine)

auxin = cytokinin -> callus formation auxin < cytokinin -> shoot formation auxin > cytokinin -> root formation

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