**5.1 Role of MYC2 in JA mediating signal transduction**


Various homologs of MYC2 like MYC3 and MYC4 binds with G-box (5′-CACGTG-3′) and G-box-related hexamers and regulate the transcription of downstream targets [29].

**53**

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

and results in the promotion of lateral root formation in Arabidopsis [32].

Various transcription factors of R2R3-MYB family like MYB21, MYB24, and MYB57 are direct targets of JAZ proteins (**Figure 6**). These TFs have significant role in mediating JA-regulated stamen development [33]. Formation of MYB-MYC complexes due to the association of MYB21 and MYB24 with the IIIe bHLH factors MYC2, MYC3, MYC4, and MYC5 controls stamen development in Arabidopsis [34]. Besides the role of JA on stamen development, JA plays a major role in seed and embryo development in tomato The *jasmonic acid-insensitive1* (*jai1*) mutant, which exhibits a loss of function of the tomato homolog of COI1, cannot set viable seeds. Moreover, production of OPDA and a residual amount of JA, in tomato mutant *acx1a*, set viable seeds. Gene silencing (*OPR3* silenced gene*)* in *SiOPR3* a transgenic line of tomato produces comparable amount of OPDA to wild type and sets only a few viable seeds; methyl-JA treatment can restore the seed setting of *SiOPR3.*This further suggests the role of methyl jasmonate in maternal control of

Numerous morphological, physiological, biochemical and molecular changes take place due to abiotic stresses like drought stress, salinity stress, high- and low-temperature stress, heavy metal toxicity, etc.; these stresses adversely affect plant growth and productivity. JA is believed to play a role in plant responses to abiotic stresses including drought, salt, and heat stress. Salinity is one of the perilous stresses that causes physiological drought and is responsible for delayed seed germination, seedling establishment and reduced growth and yield of any crop. Under salt stress, jasmonates proved to be an imperative phytohormone in mitigation. Jasmonates recovered salt inhibition on dry mass production in rice [36] and diminished the inhibitory effect of NaCl on the rate of 14CO2 fixation, protein content in *Pisum sativum* [37]. The pleiotropic effects of MeJA in protecting plants have been reported for several plants [38], reported in his studies JA is responsible for the amelioration of chilling injury, water stress, and salinity stress in *Oryza sativa* L., *Lycopersicon esculentum* L. [39], *Fragaria vesca* [40], and *Hordeum vulgare.* High-temperature stress destructively influences plant processes and disturbs the cell homeostasis [41]. Heat shock proteins (HSPs) are synthesized in plants in response to high temperature that prevent denaturation and assist refolding of

Exogenous application of JA possibly shows inhibition of primary root growth, leaf expansion, and hypocotyl elongation which ultimately leads to inhibitory action in seedling growth [30]. InsP5 enhances the interaction of COI1 with JAZ9 and the inhibitory effect of JAs on root growth [31]. JA represses leaf expansion by inhibiting the activity of the mitotic cyclin CycB1;2 and cell division, rather than by affecting cell size. Transcription factor like MYC2 and its close homologs shows both positive and negative effects on hypocotyls in red/far-red light and blue light conditions; it works positively in inhibition of hypocotyl elongation in red/far-red light and negatively regulates the inhibition of hypocotyl elongation by blue light. ERF109 binds to and activates *anthranilate synthase Α1* (*ASA1*) and *YUCCA2 (*promoters of the auxin biosynthetic genes)

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

**6.1 Inhibitory action on seedling growth**

**6.2 Role in plant reproductive development**

seed development [35].

**6.3 Role in abiotic stress tolerance**

**6. Emerging roles of Jasmonates**
