Plant Growth Regulators for Climate-Smart Agriculture

Shah Fahad, Osman Sonmez, Shah Saud, Depeng Wang, Chao Wu, Muhammad Adnan, Veysel Turan, Shah Fahad, Osman Sonmez, Shah Saud, Depeng Wang, Chao Wu, Muhammad Adnan, Veysel Turan

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000408553
• Edition: 1
• Topic: Sciences biologiques
• Subtopic: Botanique

Climatic conditions are key determinants of plant growth, whether at the scale of temperature regulation of the cell cycle or at the scale of the geographic limits for a particular species. The climate is changing due to human activities – particularly the emission of greenhouse gases – therefore the conditions for the establishment, growth, reproduction, survival, and distribution of plant species are changing. In contrast to animals, plants are able to cease and resume growth. This flexibility in their architecture and growth pattern is partly achieved by the action of plant hormones. Still, the role of plant growth regulators (PGRs) in agriculture is modest compared to other agrochemicals, such as fungicides, herbicides, and insecticides. Plant Growth Regulators for Climate-Smart Agriculture is an invaluable guide to the varied roles filled by PGRs in the attainment of higher-quality, better-yielding crops.

Salient Features (minimum 5):

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• Explores plant growth regulators and anthropogenic climate change.

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• Provides new insights related to hormonal cross-talk in plant development and stress responses.

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• Sheds new light on the role of PGRs in agriculture in the attainment of higher-quality, better-yielding crops.

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• Delivers valuable information on physiological and molecular mechanisms linked to the role of plant growth regulators in stress tolerance.

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• Provides valuable knowledge for students of agronomy, plant physiology, molecular biology, and environmental sciences.

1

Role of Gibberellins in Response to Stress Adaptation in Plants

Mousumi Mondal, Sourav Garai, Jagamohan Nayak, Anirban Roy, Debjani Dutta, Snehashis Karmakar, Shah Fahad, and Akbar Hossain

CONTENTS

1.1 Introduction

1.2 Gibberellins Biosynthesis

1.2.1 Candidate Genes in Gibberellins Biosynthesis in Plants

1.3 Roles of Gibberellins in Stress Responses

1.3.1 Gibberellins in Stress Response to Abiotic Stress

1.3.1.1 Response to Temperature Stress

1.3.1.2 Response to Salt Stress

1.3.1.3 Response to Submergence

1.3.1.4 Response to Shade

1.3.1.5 Response to Mild Osmotic Stress

1.3.1.6 Response to Soil Drying

1.3.2 Gibberellins in Stress Response to Biotic Stress

1.4 Regulation of Gibberellins in Response to Stress Protection

1.4.1 Gibberellin Biosynthesis and Signal Transduction

1.4.2 Regulation of Gibberellin Metabolism and Signalling Cascades in Response to Abiotic Stresses

1.4.2.1 Interaction between Signalling Pathways of Gibberellin and Other Plant Hormones

1.4.2.2 Regulation of GA Metabolism and Its Signalling during Abiotic Stresses

1.4.2.3 Gibberellins Signalling Integrates Various Developmental and Environmental Signals

1.5 Conclusion

References

1.1 Introduction

Several hormones, also known as plant growth regulators (PGRs) control plant growth and development and influence physiological and biochemical pathways in response to environmental stimuli for plant survival in critical situations (Davies 2010). These hormones play crucial roles when plants are exposed to abiotic stresses, such as drought, flood, or temperature stress and enable plants to check their growth, thereby conserving resources in order to survive (Bailey-Serres and Voesenek 2010). Such stresses significantly influence the biosynthesis, transportation, and signal transduction of specific stress hormones which may facilitate a protective environment. For example, stress hormones like abscisic acid (ABA) influence leaf stomata closing during dry conditions to protect the plant cell from dehydration (Wilkinson and Davies 2002). This stress hormone acts as a signalling agent to communicate the stress between roots and leaves; however, the pace of response depends upon the inter-organ stimulus which leads to hormone biosynthesis in plant leaves (Christmann et al. 2007). Gibberellins (GAs) are well-studied PGRs that play a significant role in seed germination, vegetative and reproductive growth, and fruit and seed development. Recently, they have become a crucial factor in abiotic stress tolerance (Sun 2010). Research on GAs was first conducted in Japan in the 19th century and motivated by rice disease caused by the fungus Gibberella fujikuroi (Hedden and Sponsel 2015). Later, the growth stimulatory ability of G. fujikuroi was identified, and it was concluded that this effect on plants was mediated by a toxin secreted by the fungal strain – a mixture of GAs A and GAs B (Kurosawa 1926). More recent studies have uncovered biosynthesis of GAs in plant and fungus at the molecular level in terms of pathways, enzymes, and gene regulation (Hedden and Sponsel 2015; Salazar-Cerezo et al. 2018). GAs are diterpenoid phytohormones, synthesized by plants with the help of monooxygenase, dioxygenase, and cyclase enzymes. Application of chemical growth retardants is a common agronomic practice during the early occurrence of stress to check the plant stature as a stress tolerance strategy. It has been well reported that the primary mode of action of growth retardants is to inhibit the GA biosynthesis and signalling that helps to protect the plant from exposure to stresses (Colebrook et al. 2014). This chapter includes a comprehensive discussion of GA biosynthesis, its metabolism, and signalling cascades in response to various abiotic stresses.

1.2 Gibberellins Biosynthesis

Gibberellin biosynthesis and pathway details have been studied using gas chromatography and mass spectrometry for identification of chemical nature, gene identification, and assigning them to the pathway of the entire component. GA biosynthesis comprises three sub-parts involving ent-kaurene production, conversion, and production of GA₂₀ and GA₁₉ (Hedden and Phillips 2000). GAs have resulted in a product of diterpenoid pathway and C20 precursor compound, where cyclisation initiates the process of GA biosynthesis (Hedden and Proebsting 1999). The basic component that starts GA biosynthesis involves a preliminary component of 5-Carbon compound, i.e., isopentenyl pyrophosphate (IPP), which is also a component of terpenoid compounds (Sponsel and Hedden 2010). Plants produce IPP following two approaches, one of which involves mevalonic acid and another is methyl erythritol in cytoplasm and plastids, respectively. In the initial step, ent-kaurene is produced using a soluble enzyme in proplastid. In general, the GA precursor, which is produced from ent-kaurene and GA₁₂ aldehyde, is catalysed at endoplasmic reticulum by Cytochrome P-450 monooxygenase. In the final stage, 2-oxoglutarate-dependent dioxygenases are the catalysing agents (Sun 2008). The first stage of GA synthesis follows an intermediate cyclisation process starting from GGDP via ent-copalyl diphosphate (CPP). Ent-kaurenoic acid is produced by stepwise oxidation specifically of ent-kaurene involving C19-based oxidation of ent-kaurenol and ent-kaurenal. During further oxidation, ent-kaurenoic acid is converted to ent-7α-hydroxykaurenoic acid followed by another oxidation event. In the G₁₂ branch position of the synthesis chain, a C13-hydroxylation event converts GA₁₂ to GA₅₃. Both of these GAs, i.e., GA₁₂ and GA₅₃, initiating the formation of 13-hydroxylation Gas, while a parallel for non-13 hydroxylation pathway from GA₁₂ results in GA₄ formation, respectively. GA₉ and GA₂₀ are produced following another oxidation event at C-20 position (Hedden and Thomas). GA₉ and GA₂₀ are converted to GA₄ and GA₁, respectively, involving 3-β hydroxylation, which are the ultimate steps in bioactive GA formation (Bomke and Tudzynski 2009).

1.2.1 Candidate Genes in Gibberellins Biosynthesis in Plants

Various molecular genetic studies and mutant characterisations have revealed various genes involved in the overall pathway for GA synthesis. The Arabidopsis Genome Initiative, which yielded a wealth of information during 2000, revealed the entire slate of probable candidate genes of gibberellin biosynthesis, paving the way for characterisation of all these genes (Bömke and Tudzynski 2009). Further gibberellin 13-hydroxylase cloned from rice helped to identify all respective genetic loci-contributing enzymes involved in gibberellin biosynthesis. Various GA-deficient mutants have been developed viz., ga1, ga2, ga3, ga4, and ga5 (Koornneef and van der Veen 1980). A further detailed gene characterisation study of Arabidopsis thaliana shows that GA1 encodes ent-copalyl-diphosphate synthase (Sun and Kamiya 1994), GA2 encodes ent-kaurene synthase (Yamaguchi et al. 1998), GA3 encodes ent-kaurene oxidase (Helliwell et al. 1998), GA4 encodes GA3 oxidase (Chiang et al. 1995), GA5 encodes GA20 oxidase (Afzal et al. 2017; Phillips et al. 1995). Similarly, two genes which are equivalent to GA1 and GA2 in Arabidopsis, i.e., OsCPS1 and OsKS1, were also identified in rice (Prisic et al. 2004). A total of seven enzymes are required for GA synthesis starting with GGDP. Enzymes responsible in the early steps of biosynthesis are monogenic, and, at a latter stage, gene families are responsible for enzyme synthesis (Hedden 2003). In pumpkin, one gene for KS and double copies for the same gene in Stevia rebaudiana have been reported (Sponsel and Hedden 2010) and describes stringent regulation of GA biosynthesis. GA₁₂ is the precursor of all the GAs and conversion from this compound follows two paths, one of which involves early-13 hydroxylation which is encoded by CYP714B1 and CYP714B2 genetic loci in Oryza sp. (Magome et al. 2013). Genes responsible at latter stage, viz. of the C19-GA2ox and C20-GA2ox gene family, have been well characterised in Arabidopsis and rice. A total of five C19-GA2ox, two C20-GA2ox, seven C19-GA2ox, and three C20-GA2ox have been identified in Arabidopsis (Rieu et al. 2008) and rice, respectively. Homologues of these genes are also identified in Zea mays, Pinus sp, and Phaseolus sp. (Salazar-Cerezo et al. 2018).

1.3 Roles of Gibberellins in Stress Responses

Gibberellins (GAs) are growth-promoting phytohormones of which GA₁ and GA₄ are the predominant bioactive forms (Sponsel and Hedden 2004) of more than 130 types. These perform essential roles in several developmental processes of plants, including germination of seeds, elongation of the stem, expansion of leaves, development of trichomes, maturation of pollen, and the initiation of flowering (Achard and Genschik 2009). The enzymes, viz. monooxygenases, dioxygenases, and cyclases, act as catalysts for the synthesis of GAs in plants. The degradation of DELLA proteins improves the impacts of GAs on plant growth and development (Griffiths et al. 2006) which enable the modification of plant response to stress through the cumulative response of phytohormones to stress (Miransari 2012).

As natural growth hormones, the GAs are important targets for stress-induced growth modulation, and there is increasing evidence for the involvement of GA signalling in either growth suppression or promotion, depending on the response to specific abiotic stress (Colebrook et al. 2014) or biotic stress. The phytohormone GA is found to be involved with the adaptive response to varied abiotic stresses like cold, salinity, heat, flooding, and drought (Ahmad et al. 2017; Achard et al. 2008; Colebrook et al. 2014; Khan et al. 2015).

1.3.1 Gibberellins in Stress Response to Abiotic Stress

All types of abiotic stresses are lethal for crop production and effect the performance of crop production (Adnan et al. 2018, 2019, 2020; Ahmad et al. 2019; Akbar et al. 2020; Akram et al. 2018a, b; Amanullah et al. 2020; Amir et al. 2020; Amjad et al. 2020; Arif et al. 2020; Ayman et al. 2020; Aziz et al. 2017a, b; Baseer et al. 2019; Bayram et al. 2020; Depeng et al. 2018; Fahad and Bano 2012; Fahad et al. 2013, 2014a, b, 2015a, b, 2016a, b, c, d, 2017, 2018, 2019a, b; Farah et al. 2020; Farhana 2020; Fazl...