Menthol Biosynthesis and Genetic Enhancement in Peppermint Plants

[Music] [Music] welcome to nptl online certification

course on pharmacognosy and metabolic engineering we'll now go to lecture number 45 which is the Menthol story so

where I will cover biosynthesis and pathway manipulation for enhancing the yield of

Menthol so the concepts covered first will be the biosynthetic pathway of Menthol and its

regulation and its cellular localization and next we will discuss a few case studies where attempts were

made to enhance the Menthol yield in peppermint plant through genetic engineering

approaches so Menthol is basically a monot Tarpin which I have

mentioned in one of the previous classes so the structure of Menthol just to remind

you this is menthal and

another compound uh monotor uh which is not Menthol but it's called

carvone this is car

one and that one is menal

well so this pathway originates from

map so map means it is basically operating in the plastid but

uh then the substrate is basically the gpp Geral pyop phosphate and then

gpp makes lonin and lonin subsequently converted into

either carbon or

Menthol so the major difference is here that uh one

enzyme uh which basically drives the lonin towards the carbon which is lonin six

hydroxy lonin six

hydroxy whereas the other enzyme which drives the pathway towards Menthol which is lmon in three

hydroxy carbon uh you will find in the species which is Mena

speak and Menthol you will find in the papermint which is

Mena pipera enas spata is also call this common name as

Pina so now let us see this in detail in the next slide so that means the biosynthesis now we will drop

so here at the cellular level so multiple cellular organis are involved uh for so I will put it in this

way first I will try to draw the organal and then I will put the pathway inside so consider this whole thing as a cell

so I am only putting here the the green indicates basically it's the

chloroplast okay and then I will also put uh endoplasmic

reticulum which should be here

and then another endoplasmic reticulum I have to put it

here and then I also have to put the mitochondria

here okay so this endoplasmic reticulum I have to make it

slightly larger in size oh sorry okay so now let us

write this is plasted okay

and this is endoplasmic

reticulum this is [Music] endo plasmic

[Music] reticulum and then uh this is

the Mito quria so the map pathway starts with py

and uh D Gap and

uh so we will straight away start with the uh DXs then DXs

and then it makes DX p and which M map and then subsequently I will push the

pathway in this direction finally at one point we will see the formation of

gpp so now I'll write the compound so uh this is first one is and this

is M sorry this is yeah me and the enzymes are

and then so many so many finally you will land in

gpp so the gpp is here so gppp will be converted into

limonin l i m o n e n e this

lonin will be transported out and enters into the endoplasmic reticulum so lmon I have to write it

again lonin and the enzyme responsible for this step is lonin

synthes so lonin synthes basically converts gpp to lonin and lonin now

moves inside the endoplasmic reticulum and where by the action of this enzyme

l3h which is the three hydroxy lonin 3 hydroxy which converts lmon to so I put

l3h l3h yeah which converts lmon into trans isoptin so

trans ISO pad

isol so this transpo isop pipol will be subsequently converted into ISO

piperon so the trans hyperon will now moved into the

mitochondria and where it is converted into isopar ton so this

is trans ISO

P reol now converted into

ISO pper ton okay this isopar Tenon will come out

from the mitochondria into the cytool and then so I have to put the writing again

ISO P tone and which will be converted into

ISO polyon C isop polyon so C ISO

po G and C isop polygon subsequently converted into polygon so I put the

arrow and then this poon uh we'll move one in one root polygon will move

inside the uh endoplasmic reticulum again and where it will be converted into menthofuran

if you are n you okay

whereas in another case this polyon will be converted into Menon so pulan can be converted into

either menthon or also is Menon so Menon

or Isom menthon okay and from menthon Menthol is

finally synthesized and from Isom menthon

isomenthol can be formed and also NE isomenthol can also be

formed new isomenthol can be form new

ISO menol can also be formed so we put the arrow here okay so this step basically

occurring in the cytool okay now it is also possible that M MBA

pathway contributes towards the Menthol biosynthesis but much later it was found that in fact NBA pathway is not

contributing to Menthol biosynthesis because there are some blockage exist in the late steps of MBA pathway therefore

I am not showing the MV pathway here so as you know the MBA pathway operates in the cytool so you can uh keep a space

for this so this is basically the me pathway and here is the space

for MV pathway which is not really contributing towards the uh Menthol

biosynthesis now uh this is about uh okay now there are few enzymes I have to put it here uh for

example this uh important enzyme the MFS menthofuran

synthes so Ms MFS will be here menopur and synthes

and IPR will be here which converts isop piperon to isopon

so and another important enzyme is

ipgi let okay so I make it simple as simple as I can

so ipgi yes s isop poon isomes ipgi I can put it here

so ipgi stands for CIS isopon isaris and IPR stands for Trans isop

piperon reductors so R is basically reduct is and this is

basically Isis okay and IP DH is also

there which is basically a dehydrogen is now next what we see what is happening

in case of carbon so carbon what is this that the lonin uh because lonin moved to

endoplasmic reticulum in in case of Mena uh spata the lonin formed in the uh plastid

moves into the endoplasmic reticulum so I will put the lmon in here

and this lonin will be converted into trans carvol TR r e n

s c a r v e o l this trans Carval will come out from

the endoplasm reticulum into the cytool so trans

and this trans Carval will be converted into Carbone so now I will add the arrow well so you should not be confused

so therefore this endoplasmic reticulum I will remove it from

here instead I will uh prefer to put it here inside so

the enzyme is limonin 6 hydroxy which is here

l6h and then there is a CDH trans Carval dehydrogenase so which converts trans

Carval to carbon so this is CDH so these two are the meas

enzyme converting lonin into carbon and this one particularly you will find in that species what is that which is Mena

spicata whereas the other pathway is operating in the Mena pipera the

pment so this is basically in brief in the most simplified way the uh I I represented the pathway of

Menthol and carbon biosynthesis okay one important enzyme I must put it which is menthol

reduce which should come here which should be menthon Menthol reductors so or I can put it simply

write it Mr Mr stands for Menon

reductors and pogon to menthon formation this is called

PR that means again poon reductors

well so this is in brief the pathway and which which operates uh starting from plastid involving endoplasmic

reticulum and mitochondria and finally to the cytool so this is basically in brief the pathway also Menthol can be

converted into meny acetate acetate as well

so so now what we will see we'll see the regulation of the pathway and where we will find the Menthol in the plant

so next slide so this is localization of the

Menthol so the place where these menthols are synthesized and accumulate is called

triome so I will draw a structure of a triome to show you here these are called glandular triome

because this forms a typical gland I just uh draw

it this is called the stock cell and then above it these are called secretary

cells and then top of it will be

the subc oil storage cavity so this is this is the oil

storage Cav cavity this is also subicular this is the stock

cell and this is called the thisel

cell and these are called secretary

cells so the products are synthesized then from here it secretes

here so this is basically filled up with essential oil where menol is the m component so this is basically the

structure of one such glandular

triome there are two type one is called Pate another is called capitate so if it has a stock it is capitate if the stock

is not there proper so it is basically beled okay now next is the regulation of menthol bi

synthesis there a problem with m regulation of Menthol

biosynthesis so basically there it's it can be divided into two periods one is the two distinct period one is the first

period so which is basically picks around 12 days of leaf initiation that

means F at about 12 Days

After Leaf initiation so where what you will find here in this stage you will find oil

glands filling with the essential oil and

conversion of precursors to

menthon and also pon pon and Muran are

also detected U and this will be followed by the

second period so which is basically

one week later so in this period what you will see that

the transcripts and the

enzymes both will be diminished and then important point is is gradual

increase of of Menon reduced

activity Mr resulting in depletion

of Menon and concomitant

increase in Menthol okay so Leaf surface contains

glandular triom and when you touch the leaf of this men menas species basically you are by touching you are breaking

down the glandular triom and if you smell your hand you will get the aroma because what happens you you are

basically uh breaking down this uh this subc oil storage cavity which is very delicate and that is this one if it is

broken down then that leads to the release of the essential oil okay so this is brief about the regulation of

Menthol biosynthesis I will end this lecture here and in the next class I will

continue this topic to complete the total theme so that is menthol story so thank you very much