Plant nuclear genome organization

1. PLANT NUCLEAR GENOME ORGANIZATION
The plant nuclear genome consists of deoxyribonucleic acid (DNA)
divided among the chromosomes within the cell nucleus. Plant
genomes contain coding and regulatory sequences for genes and
repetitive DNA.
➢ Plant genome is organized into chromosomes
➢ Genome sizes are diverse from 63-1,49,000 Mb
➢ Structural features of chromosomes like centromeres, telomeres and
chromatin packaging are well-conserved
➢ The plant nuclear genome consist of DNA and associated proteins
➢ It is organized into discrete chromosomes
➢ unreplicated chromosome and metaphase chromatid consists of a
single DNA molecule that is linear

2. Proteins
➢ There are 2 types of proteins found in DNA Basic proteins-Positive
charge at neutral pH Histone (H1, H2A, H2B, H3 and H4 )
➢ Acidic proteins- Negative charge at neutral pH Non-histone
proteins
DNA PACKING:
➢ Nucleosome contains Eight histone protein molecules, these being
two each of histones H2A, H2B, H3 and H4
➢ These eight proteins form a barrel shaped core octamer with the
DNA twice around the outside
➢ 140 to 150 bp of DNA are associated with the nucleosome particle
and each nucleosome is separated by 50-70 bp of linker DNA
constituent of chromatin
➢ DNA= 20-40 %- most important chemical constituent of chromatin
➢ RNA=05-10 %-associated with chromatin as;
⚫ Ribosomal RNA-( rRNA)
⚫ Messenger RNA- (mRNA)
⚫ Transfer RNA- (tRNA)
➢ PROTEINS=55-60%-associated with chromatin
TYPES OF CHROMATIN

3. Euchromatin
➢ Lightly packed form of chromatin that is rich in gene concentration
➢ takes up light stain and represent most of the chromatin, that
disperse after mitosis has completed.
➢ Consists of structural genes which replicate and transcribe during
G1 and S phase of the interphase.
➢ Considered genetically active chromatin, since it has a role in their
phenotypic expression of the genes.
Heterochromatin
➢ Tightly packed form of chromatin that takes up deep stain during
interphase and prophase but metaphase takes up light stain.
➢ Chromomeres, centromeric regions, and knobs also take up dark
staining, of which centromeric regions and knobs are the true
Heterochromatic.
➢ In the chromosomes all the centromeres fuse to form a long
Heterochromatic mass called chromocentre.
➢ Heterochromatin consists of highly repetitive DNA sequences.
CENTROMERE
➢ The centromere is the specialized DNA sequence of a
chromosome that links a pair of sister chromatids
➢ During mitosis, spindle fibers attach to the centromere via the
kinetochore.

4. TELOMERE
➢ sequences consist of short tandem repeats that contribute to the
stability and integrity of the chromosome

5. NUCLEAR GENOME
Single-or low-copy sequences
➢ Single copy DNA refers to any DNA sequence present in only one
copy per haploid genome.
➢ It contain INTRON AND EXON
➢ The average
coding region of
plant gene requires about 1,300 bp or 15,000 genes.

6. Repetitive DNA-non coding
Repeated sequences are patterns of nucleic acids (DNA) that occur in
multiple copies throughout the genome Repetitive DNA can be present
in hundreds or even thousands of copies in the genome Repetitive DNA
can be subdivided into 2 classes
• Tandem repeats
• Dispersed
repeats
Tandem repeats
➢ Much of the repetitive DNA falls into the tandem repeats is referred
to as satellite DNA
➢ It is a non-coding DNA seq
➢ Satellite DNA is

7. a ssociated with
centromere or telomeres and is heterochromatic
Moderately repetitive DNA includes:
➢ minisatellites
➢ Microsatellites
➢ variable number tandem repeats (VNTRs)
Dispersed repeats
➢ Dispersed repeats are segments of DNA that occur multiple times at
more or less random positions in the genome.
➢ They are typically transposable elements, large segments that
encode a protein responsible for the moving of the segment from
one site to another.
Transposable elements
➢ DNA transposons
➢ Retrotransposons
DNA transposons
➢ DNA transposons it also called JUMPING GENE.
➢ Eukaryotic genomes contain an abundance of repeated DNA, and
some repeated sequences are mobile.
➢ Transposable elements (TEs) are defined as DNA sequences that are
able to move from one location to another in the genome.
➢ It move from one genomic location to another by a cut-and-paste

8. mechanism.
REFERENCE
1. https://www.researchgate.net/publication/228052081_Plant_Nuclear
_Genome_Composition
2. Capelson M, Liang Y, Schulte R, Mair W, Wagner U, Hetzer MW
(2010) Chromatin-bound nuclear pore components regulate gene
expression in higher eukaryotes.
3. Alkhimova, O.G., Mazurok, N.A., Potapova, T.A., Zakian, S.M.,
Heslop‐Harrison, J.S. and Vershinin, A.V. (2004) Diverse patterns of
the tandem repeats organization in rye chromosomes.