4-Coumaroyl and Caffeoyl Shikimic Acids Inhibit 4-Coumaric Acid: Coenzyme A Ligases and Modulate Metabolic Flux for 3-Hydroxylation in Monolignol Biosynthesis of Populus trichocarpa

Abstract

In a number of plant species, downregulation of 4-coumaric acid: coenzyme A ligase (4CL) can reduce lignin content. In lignin precursor (monolignol) biosynthesis during stem wood formation in Populus trichocarpa, two enzymes Ptr4CL3 and Ptr4CL5 catalyze the CoA ligation of 4-coumaric acid to 4-coumaroyl-CoA and caffeic acid to caffeoyl-CoA. CoA ligation of 4-coumaric acid is essential for the 3-hydroxylation of 4-coumaroyl shikimic acid. This hydroxylation results from sequential reactions of 4-hydroxycinnamoyl-CoA: shikimic acid hydroxycinnamoyl transferases (PtrHCT1 and PtrHCT6) and 4-coumaric acid 3-hydroxylase 3 (PtrC3H3). Alternatively, 3-hydroxylation of 4-coumaric acid to caffeic acid may occur through an enzyme complex of cinnamic acid 4-hydroxylase 1 and 2 (PtrC4H1 and PtrC4H2) and PtrC3H3. We found that 4-coumaroyl and caffeoyl shikimic acids are inhibitors of Ptr4CL3 and Ptr4CL5. 4-Coumaroyl shikimic acid strongly inhibits formation of 4-coumaroyl-CoA and caffeoyl-CoA. Caffeoyl shikimic acid inhibits only formation of 4-coumaroyl-CoA. 4-coumaroyl and caffeoyl shikimic acids both act as competitive and uncompetitive inhibitors. Estimates of metabolic flux in wildtype and PtrC3H3 downregulated P. trichocarpa transgenics have been made using LC-MS/MS based absolute protein and metabolite quantification, mass action kinetics and inhibition equations. Inhibition by 4-coumaroyl and caffeoyl shikimic acids may play significant regulatory roles when these inhibitors accumulate.

Characterization of the Gh4CL gene family reveals a role of Gh4CL7 in drought tolerance

“…Lignin is the second largest polymer in plants after cellulose [47]. It provides mechanical support to plants by increasing cell wall hardness and enhancing compressive strength of cells [48,49]. We found that repressing the expression level of Gh4CL7 in G. hirsutum reduced the lignin content and led to a reduction in drought resistance, consistent with the result of rice plants with a decreased lignin content being more prone to drought stress [50].…”

Characterization of the Gh4CL gene family reveals a role of Gh4CL7 in drought tolerance

“…Lignin is the second largest polymer in plants after cellulose [59]. It provides mechanical support to plants by increasing cell wall hardness and enhancing compressive strength of cells [60][61][62]. We found that repressing the expression level of Gh4CL7 in G. hirsutum reduced the lignin content and led to a reduction in drought resistance, consistent with the result of rice plants with a decreased lignin content being more prone to drought stress [63].…”

Comparative analysis of transcrptome profiling to identify genes involved in bulged surface of pear fruits (Pyrus bretschneideri Rehd. cv. Yuluxiangli)

“…In addition, it had been reported that, phytohormones, lignin synthesis related genes such as phenylpropane metabolic pathway genes CYP73A2 and COMT [44,21,22], transcriptional factor genes bHLH and MYB, as well as cellulose synthetase genes were involved in vascular tissue, growth, development and metabolism of its secondary cell wall. On the other hand, bHLH genes played an important role in early vascular bundle development [45,46].…”

“…Thus, lignin plays important roles in increasing the strength of the cell wall and enhancing the ability of water transport in plants [20]. In lignin biosynthesis process, some genes such as F5H (ferulic acid-5-hydroxylase), 4CL (4-coumaric acid CoA ligase) and COMT (caffeic acid/5-hydroxyferulic acid-O-methyltransferase) genes could also affect the growth and development of vascular tissue [21][22][23]. In addition, bHLH transcription factor, such as target of monoperos 5 (tmo5) interacted directly with ARF (auxin responsive gene), and playing a significant role in the procambium tissue, where the vascular bundles split and bHLH interacted directly with another bHLH transcriptional factor LHW to act on ARF5/MP [24,25].…”