1) The eui gene controls elongation of the uppermost internode in rice, allowing panicles to emerge from leaf sheaths. This helps overcome the problem of "panicle enclosure" in hybrid rice production. 2) EUI1 encodes an enzyme that deactivates bioactive GAs in rice. Mutations in EUI1 result in increased bioactive GAs and elongated internodes. 3) HOX12 regulates EUI1 expression - higher HOX12 promotes EUI1 and limits GA levels, while lower HOX12 reduces EUI1 and increases GAs, enhancing panicle exsertion.

1. eui Gene
PRESENTED BY,
S.DIVYA.
2017600805(I M.Sc –GPB)

2. Need of eui gene(Elongated UPPERMOST
NODE)
• The adoption of hybrid rice caused the second leap in rice yield after the
‘green revolution’ and contributes substantially to food security of China
and the world.
• Male sterile cultivars play an important role in the production of such
hybrid rice .
• However, almost all cytoplasmic male sterile lines (A lines) as females of
hybrid rice have a natural deficiency of ‘panicle enclosure’.

3. • Natural deficiency of ‘panicle enclosure’ blocks pollination between the A line
and the fertility restorer line as the male (R line) of hybrid rice and decreases
seed yield.
• In hybrid rice seed production, exogenous ‘920’ (the active ingredient is
gibberellin A3) must be applied to eliminate or alleviate panicle enclosure of the
A line
• This not only increases production cost and pollutes the environment and also
decreases the seed quality.

4. Reason for Natural deficiency of panicle
enclosure
• The occurrence of cytoplasmic male sterility (CMS) in the A line caused a
deficiency of indole-3-acetic acid in the panicle
• It consequently caused a decrease of gibberellin A1 (GA1) in the uppermost
internode (UI) by down-regulating the expression of OsGA3ox2 (Yin et
al.,2007).
• The reduced GA1 resulted in a shortened UI, and therefore, the panicle could
not be pushed out of the flag leaf sheath.

5. Initial Discovery of EUI Gene
• Rutger and Carnahan (1981) identified a tall rice mutant (76 : 4512) with
elongated internodes.
• Genetic analysis showed that this trait of internode elongation was controlled by
a single recessive gene designated as eui. (elongated uppermost internode).
• Rutger and Carnahan (1981) proposed that eui could be used to develop a tall R
line, which may facilitate wind dispersal of pollen from the tall R line onto the
short A line in hybrid seed production.

6. Tall R line X semi-dwarf A line
semi-dwarf
Since tallness is controlled by eui was recessively inherited.
The semi-dwarf is known to be more productive than the tall plant
type (Rutger and Carnahan, 1981).

7. EUI gene to overcome panicle enclosure
• Besides developing tall R lines, the other use of eui is the introduction
into an A line to improve its panicle exsertion and solve the problem
of panicle enclosure.
• A tall A line containing eui is called an e-type A line and
its corresponding hybrid is an e-type hybrid.

8. Initial drawbacks of EUI gene
• Introducing the eui gene into parental lines by conventional hybridization and
back-crossing programme often resulted in change in some good agronomical
traits of the original hybrid due to ‘linkage drag’ (Zhang and Yang, 2004), in
which undesired genes close to eui were introduced together with eui.
• To avoid linkage drag Yang et al. (2002) proposed generating A lines or e-type
R lines by direct mutagenesis of the parental lines of hybrids instead of
hybridization and backcrossing

9. Achievement
• The seed production of e-hybrids using e-type A lines as the parent
needs less or no exogenous 920.
• and their morphology, growing period and yield are regularly not
significantly different from the original hybrids (Zhang et al., 2009).

10. eui mutant….
• In rice, GA1 is the predominant bioactive form in vegetable tissues, while
GA4strongly accumulates in panicles (Hirano et al., 2008).
• EUI1 encodes a P450 monooxygenase that epoxidizes GAs (GA4, GA9, and GA12) in
a deactivation reaction. (‘panicle enclosure’)
• The eui1 mutants exhibit enhanced internode elongation and panicle exsertion;
accordingly, increased amounts of bioactive GA4 accumulate in the uppermost
internodes of these mutants (Luo et al., 2006; Zhu et al., 2006)

11. wild
eui mutant
wild
eui mutant

12. MECHANISM

13. EUI
• EUI1 is considered to function mainly in the uppermost internode. In fact,
this gene is highly expressed in anthers and spikelets but is expressed at
relatively low levels in the uppermost internodes (Magome et al., 2013).
• Deactivation of bioactive GA4 in anthers is catalyzed by EUI1, which
epoxidizes GAs and regulates the influx of GA4 into the stem from panicles.

14. • Consequently, when EUI1 loses its function, increased amounts of GA4 flow
into the uppermost internode, leading to the elongation of this internode.
• Recently, two homologous genes of EUI1, CYP714B1 and CYP714B2, were
functionally characterized in rice.
• Compared with EUI1, CYP714B1 and CYP714B2 are highly expressed in
spikelets and in the uppermost internodes of adult plants.

15. HOX12 Acts as a Transcriptional Activator
• HOX12 participates in the regulatory network orchestrating panicle
exsertion by directly regulating EUI1 expression
• Activation of HOX12 leads to GA deficiency, with a dwarf phenotype and
defective panicle exsertion, which is also observed in EUI1 overexpressors.
• HOX12 knockdown plants exhibit elongated internodes with enhanced
panicle exsertion, which is similar to the eui1 mutant
•

16. SIMILARITY BETWEEN HOX12 and eui 1
• Both HOX12 knockdown and eui1 plants are morphologically normal until
increased elongation of the uppermost internode occurs at the heading
stage
• Quantitative analysis of GA biosynthetic intermediates demonstrated that
non-13-hydroxy GAs (GA12, GA15, GA24, GA9, and GA4) accumulate in the
uppermost internodes of HOX12 knockdown plants, which was also
observed in eui1mutants (Luo et al., 2006; Zhu et al., 2006).

19. Working Model Of The Role Of HOX12 In
Developmental Process

21. • EUI1 acts as a switch and regulates the influx of GA4 into the stem
from panicle.
• HOX12 directly regulates the expression of EUI1 by binding to its
promoter.
• Enhanced HOX12levels promote EUI1 expression and inhibit
GA4 accumulation.
• Bycontrast,diminished HOX12 expression downregulates EUI1 activity
and consequently promotes the influx of GA4 into the stem, leading to
enhanced panicle exsertion.