Plant hormones are versatile chemical regulators of plant growth

Abstract

The plant hormones are a structurally unrelated collection of small molecules derived from various essential metabolic pathways. These compounds are important regulators of plant growth and mediate responses to both biotic and abiotic stresses. During the last ten years there have been many exciting advances in our understanding of plant hormone biology, including new discoveries in the areas of hormone biosynthesis, transport, perception and response. Receptors for many of the major hormones have now been identified, providing new opportunities to study the chemical specificity of hormone signaling. These studies also reveal a surprisingly important role for the ubiquitin-proteasome pathway in hormone signaling. In addition, recent work confirms that hormone signaling interacts at multiple levels during plant growth and development. In the future, a major challenge will be to understand how the information conveyed by these simple compounds is integrated during plant growth.

Euglena gracilis(Euglenophyceae) produces abscisic acid and cytokinins and responds to their exogenous application singly and in combination with other growth regulators

“…These molecules individually or cooperatively direct the metabolism of individual cells and carry information between cells, thereby coordinating growth and development. Several groups of physiologically active hormone compounds are ubiquitous among higher plants, such as auxins, cytokinins, gibberellins and abscisic acid (Santner et al, 2009). These endogenous growth regulators have also been detected in various algal taxa in concentrations comparable to those of vascular plants.…”

“…Abscisic acid (ABA) is a phytohormone that plays an important role in plant responses to environmental stress and plant pathogens (Jiang & Hartung, 2008;Santner et al, 2009). The general functions of ABA in vascular plants are to inhibit precocious germination and promote dormancy in seeds, and production of molecules that protect cells against desiccation (Nakashima & Yamaguchi-Shinozaki, 2013).…”

Modulating plant hormones by enzyme action

“…The jasmonates (JA) play roles in seed germination, fertility, root growth and pathogen responses. [1][2][3] Perception of IAA and JA by either the SCF TIR1 ubiquitin ligase complex [6][7][8][9] or the SCF COI1 ubiquitin ligase complex, [10][11][12] respectively, recruits different classes of transcriptional modulators (i.e., Aux/ IAA proteins and JAZ proteins, respectively) to the complex for ubiquitination. Degradation of Aux/IAA proteins modulates expression of auxin-responsive genes…”

“…The GH3 family of acyl acid amido synthetases Corey S. Westfall, 1 Changes in cellular hormone concentrations and the chemical structure of a hormone will affect interaction with cognate receptors and alter developmental processes and responses. Biochemically, the levels and molecular structure of plant hormones are modified by the rates of their biosynthesis, catabolism, and/or modification.…”

Auxin-Binding Protein 1 is a negative regulator of the SCFTIR1/AFB pathway

“…This predominant role of auxin relies on its critical involvement in the regulation and coordination of cell division, cell expansion and differentiation that sustain growth, initiation and formation of new organs or adaptive responses to environmental stimuli 1,2 . Within the last decade, molecular and genetic evidence established the importance of auxin-mediated transcriptional responses involving the auxin coreceptors transport inhibitor response 1/auxin-related F-box proteins (TIR1/AFB) and auxin/indole-3-acetic acid (AUX/IAA) repressors 3,4 . Auxin favours AUX/IAA recruitment by TIR1/AFBs within SCF TIR1/AFB ubiquitin ligase E3 complexes that promotes their polyubiquitination and degradation through the ubiquitin/26S proteasome system (UPS) 3,5 .…”