**4. Biosynthesis of jasmonates: the octadecanoid pathway**

The biosynthetic pathway of jasmonates (**Figure 4**) was identified in Year 1984. The scientists Vick and Zimmerman [17] were the first to illustrate the biosynthetic pathway in a simplified manner which indicated that linolenic acid could be converted into the cyclopentanone 12-oxo-phytodienoic acid (12-oxo-PDA) through lipoxygenase enzyme. Methodically the pathway was studied in model plants like Arabidopsis and tomato. The octadecanoid pathway of Jasmonates completes in two cellular organelles such as chloroplasts and peroxisomes and are considered to be the primary sites [7, 18]. α-Linolenic acid (α-LeA) released from galactolipids (due to wounding or pathogens attack) of chloroplast membranes is found to be the main player of MeJA and JA production [12]. Phospholipases1 (PL1), lipoxygenase, allene oxide synthase, and allene oxide cyclase (AOC) are significant enzymes involved in biosynthesis of jasmonates.

**51**

JAZ (NINJA).

*Jasmonates: An Emerging Approach in Biotic and Abiotic Stress Tolerance*

**4.1 Role of enzymes involved in jasmonates biosynthetic pathway**

• **Phospholipases:** formation of α-LeA from chloroplastic membrane lipids

• **13-Lipoxygenase (LOX):** addition of oxygen molecule to α-LeA and results in formation of an intermediate compound 13-hydroperoxy-9,11,15-octadecatrienoic

• **Allene oxide cyclase (AOC):** formation of 12-oxo-phytodienoic acid (12-OPDA)

• **Allene oxide synthase (AOS):** oxidation of 13-HPOT to allene oxide

The AOS and AOC are present in plastids and they act in concert [19]. 12-OPDA is the final product of biosynthetic pathway formed in chloroplast and undergoes three cycles of β-oxidation in the peroxisomes [8] A methylation reaction by JA methyl transferase results in the formation of jasmonate methyl ester derivative, i.e., methyl jasmonate. Among the six 13-LOXs of Arabidopsis, four of them are (LOX2, LOX3, LOX4, and LOX6) but LOX2 is a vital lipoxygenase in

• Responsible for the bulk of JA formation upon wounding [7, 20]

• Oxylipin generation during natural and dark-induced senescence

Several transcription factors (TFs), repressors, up- regulation and down-regulation of certain genes, and members of ubiquitin-proteasome complexes are involved in JA signal perception and transduction pathway (**Figure 5**). Different independent studies [21, 22] with GC-MS and HPLC analyses in *A. thaliana* revealed that (+)-7-iso-JA-L-Ile

The Skp1/Cullin/F-box (SCF) complex is of proteinous type and is the ubiquitinproteasome complex. In jasmonate signal transduction pathway *coronatine insensitive1* (*COI1*)*,* the locus encodes an F-box protein that associates with its other counterparts, SKP1, Cullin, and Rbx proteins, to form an E3 ubiquitin ligase [23]. So *COI1* is found to be the jasmonate receptor in signaling pathway. In 2007, [22, 24, 25] scientists in independent research found new family of proteins called jasmonate zim-domain (JAZ) proteins in Arabidopsis, which were found to be the key negative regulator of JA signaling and act as substrate for SCF*COI1* E3 ubiquitin ligase complex. About 12 JAZ proteins were present in *A. thaliana* and contain N-terminal domain, a highly conserved C-terminal Jas domain that mediates the interaction with the *COI1* and several transcription factors, and the conserved protein–protein interaction domain, the ZIM (TIFY) domain that helps in JAZ dimerization and interaction with novel interactor of

Moreover, the interaction of *COI1* with the Jas domain of JAZ proteins in the presence of JA-Ile forms the co-receptor complex [26] SCF*COI1*, E3 ubiquitin ligase complex, JAZ degrons (*JAZ1* to *JAZ12*) and IP5 form the co-receptor complex and

**5. Jasmonates signal perception and transduction pathway**

is the only natural and direct JA-signaling ligand in plants.

found to be true jasmonates receptors [27].

*DOI: http://dx.doi.org/10.5772/intechopen.84608*

an unstable compound from allene oxide.

acid (13-HPOT).

JA biosynthesis.

**4.2 Key roles of LOX2**

**Figure 4.** *Step wise pathway of jasmonates biosynthesis. Source: Ahmad et al., [16].*
