**4. Conclusion**

**Gene <sup>1</sup>**

1

210 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

16

3

1

3

2

2

Cinnamoyl-CoAreductase (*AhCCR*)

Cinnamyl alcohol dehydrogenase (*AhCAD*)

Caffeoyl CoA 3-Omethyltransferase (*AhCCoAOMT*)

4-Coumaroyl shikimate 3-hydroxylase/ pcoumarate 3-hydroxylase

Ferulic acid hydroxylase

Hydroxycinnamoyl CoA:

hydroxycinnamoyl transferase (*AhHCT*).

(*AhC3H*)

(*AhF5H*)

shikimate

1

Caffeic acid Omethyltransferase (*AhCOMT*)

**No. Seq. Function in stress Reference(s)**

[189,190]

[189,191,192]

[193–195]

[196]

[193,197]

[198–201]

[202]

In wheat, this gene is involved in pathogen defense signaling. In tomato and other plants, the repression of this gene produced severe development-related phenotypes.

The silencing *CAD* led to changes in the lignin structure, fiber

This gene can be highly induced by drought and cold stress, suggesting a possible role in plant abiotic stress resistance. In maize and wheat, *CCoAOMT* is involved in the mechanism of resistance/susceptibility against fusariosis and powdery

C3H downregulation led to a dramatic accumulation of several glucosides of *p*-coumaric acid, including phenylglucosides (populoside, grandidentatin, and trichocarposide). This modification may be an acceptable strategy to increase the secondary metabolite diversity against pathogens.

In wheat, silencing of this gene is linked to increased susceptibility to fungal pathogens, such as *Blumeria graminis*.

*F5H* transcripts accumulated in the leaves in response to mechanical wounding or the application of related elicitors, such as ethylene, ABA, and hydrogen peroxide (H2O2). *f5h* mutants were unable to develop normally under UV light, probably because of a lack of UV-radiation protective synapate esters. This gene is essential for expression of anthocyanin biosynthesis-associated genes and anthocyanin accumulation

Downregulation of the HCT gene in alfalfa plants exhibited constitutive activation of defense responses, triggered by release of bioactive cell wall fragments and production of hydrogen peroxide generated as a result of impaired secondary

Conversely, it led to an augmented resistance to *Hyaloperonospora arabidopsidis* in Arabidopsis.

under photo-oxidative stress.

cell wall integrity.

Number of genes detected in the grain amaranth transcriptome [14].

**Table 5.** Lignin biosynthetic pathway genes identified in grain amaranth

quality, and/or improved digestibility. It also led to development related phenotypes during vegetative and reproductive stages. Pathogen resistance was also modified. Phylogenetic analysis suggests that the *AhCAD2* gene could be

involved in stress tolerance responses.

mildew, respectively.

The several hypotheses raised by the discovery of the numerous stress-related phenylpropa‐ noid genes in grain amaranth represents a strong incentive for the initiation and subsequent deepening of secondary metabolite studies in *Amaranthus* plants, which may yield promising results in various areas of interest, including food science and nutrition, medicine and stress plant physiology, among others.
