Bilin Metabolism in Plants: Structure, Function and Haem Oxygenase Regulation of Bilin Biosynthesis

Abstract

Bilins are open‐chain tetrapyrroles with a wide range of visible and nearly visible‐light absorption and emission properties. The linear tetrapyrrole molecules function as chromophores of the light‐harvesting phycobiliproteins and phytochrome‐mediated light sensing in photosynthetic organisms. They are derived from the cyclic precursor haem. The initial step in bilin biosynthesis is the conversion of haem into biliverdin (BV IX α) catalysed by haem oxygenase, which is subsequently reduced to specific bilins by ferredoxin‐dependent bilin reductases (FDBRs). Bilins usually bound to apoproteins via single or double covalent bonds to form a macromolecular complex phycobilisomes. The attachment of apoproteins to bilin is an autocatalytic process, but bilin lyases are required for the specific attachment of bilin chromophores to phycobiliprotein apoproteins. Besides the biosynthesis, structure and functions of bilins, this article also aims to recapitulate and discuss the current progress in the field of bilins and to emphasise the emerging areas. Key Concepts Bilins are open‐chain tetrapyrrole non‐metallic colour compounds formed as a metabolic product of protoporphyrin IX. Biliverdin IX α is the common precursor of all naturally occurring bilins. Haem oxygenase (HO) and ferredoxin‐dependent bilin reductases (FDBRs) are the two key enzymes involved in the biosynthesis of bilins. Phycobiliproteins assemble with bilins to form phycobilisomes, which help in light harvesting and energy transfer. Bilin plays a significant role in various physiological processes, namely, photosynthesis, respiration, light perception, signalling, cell defence against oxidative stress, nitrate and sulfate assimilation and programmed cell death.

Role of Engineered Carbon Nanoparticles (CNPs) in Promoting Growth and Metabolism of Vigna radiata (L.) Wilczek: Insights into the Biochemical and Physiological Responses

“…Heme-oxygenase is a novel discovered enzyme in higher plants that works as an antioxidant against different environmental stress, namely salinity, UV-B and heavy metal stress [ 10 , 11 , 12 , 13 ]. The enzyme catalyzes the oxidative degradation of Fe (III) protoporphyrin IX to biliverdin IX (BV), carbon monoxide (CO) and iron in the presence of a reducing equivalent (NADPH) [ 14 , 15 , 16 ]. These antioxidants show regular activity during normal conditions, but their catalytic reaction is magnified under changing environments [ 10 ].…”

Nitric oxide mitigates salt-induced oxidative stress in Brassica juncea seedlings by regulating ROS metabolism and antioxidant defense system

“…Increasing salinization of soil and water is a global concern which affects the agricultural production worldwide. This problem becomes greater in the region with dry climate, infrequent rainfall and extreme temperature leading to high evapotranspiration rate (Hasanuzzaman et al 2018;Khator et al 2019;Mahawar and Shekhawat 2019). All of these characteristics are common in arid and semiarid regions of India.…”

“…In fact, the United Nation Environment Program estimated that approx 20% of irrigated agriculture land in the world is affected by soil salinity (Hasanuzzaman et al 2018). Salinity stress influences various physiological and metabolic pathways of the plant which mainly depends on concentration and duration of stress that eventually leads to a diminution in crop production (Verma et al 2015;Khator and Shekhawat 2019;Khator et al 2020). In plant soil, NaCl is the most prevalent and soluble salt and its elevated concentration incite two principal effects on plant; osmotic stress and ion toxicity.…”

“…Consequently, salinity stress is regarded as hyperosmotic stress. Moreover, increased concentration of Na + and Cl − in the cytosol causes a severe ionic imbalance which leads to electrolyte leakage and also affects the substantial physiological disorders including membrane disruption, nutrients imbalance; impairment in the ability to neutralize the reactive oxygen species and variation in antioxidant enzyme activity (Mahawar and Shekhawat 2016;Khator and Shekhawat 2019). Photosynthetic inhibition and fractional closure of stomata are other negative consequences of salt stress which constitutes to restrict plant development and productivity (Ahmad et al 2016).…”

“…chloroplast, mitochondria and peroxisome, thus causing the oxidative burst in terms of peroxidation of lipid, oxidation of protein and nucleic acids (Hasanuzzaman et al 2018) which ultimately reduces the plant growth and production (Fatma et al 2016;Ahmad et al 2016). To minimize the oxidative stress, plants have developed potential antioxidant defense system to counteract ROS mediated toxicity (Verma et al 2008;Shekhawat et al 2008Shekhawat et al , 2009Shekhawat et al , 2010Shekhawat et al , 2019Khator and Shekhawat 2020). The antioxidant defense system comprises non-enzymatic antioxidants which include; ascorbic acid (AsA), glutathione (GSH), proline, phenolic compounds, alkaloids, non-protein amino acids, and α-tocopherols and enzymatic antioxidants include; superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), guaiacol peroxidase (GPX) and glutathione S-transferase (GST) (Hasanuzzaman et al 2012;Verma and Shekhawat 2012;Khator and Shekhawat 2018;Mahawar and Shekhawat 2018;Mahawar et al 2018a).…”