Drought and heat are major abiotic stresses that reduce crop productivity and weaken global food security, especially given the current and growing impacts of climate change and increases in the occurrence and severity of both stress factors. Plants have developed dynamic responses at the morphological, physiological and biochemical levels allowing them to escape and/or adapt to unfavourable environmental conditions. Nevertheless, even the mildest heat and drought stress negatively affects crop yield. Further, several independent studies have shown that increased temperature and drought can reduce crop yields by as much as 50%. Response to stress is complex and involves several factors including signaling, transcription factors, hormones, and secondary metabolites. The reproductive phase of development, leading to the grain production is shown to be more sensitive to heat stress in several crops. Advances coming from biotechnology including progress in genomics and information technology may mitigate the detrimental effects of heat and drought through the use of agronomic management practices and the development of crop varieties with increased productivity under stress. This review presents recent progress in key areas relevant to plant drought and heat tolerance. Furthermore, an overview and implications of physiological, biochemical and genetic aspects in the context of heat and drought are presented. Potential strategies to improve crop productivity are discussed.

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Heat and Drought Stresses in Crops and Approaches for Their Mitigation.

Phenylpropanoid metabolism is one of the most important metabolisms in plants, yielding more than 8,000 metabolites contributing to plant development and plant-environment interplay. Phenylpropanoid metabolism materialized during the evolution of early freshwater algae that were initiating terrestrialization and land plants have evolved multiple branches of this pathway, which give rise to metabolites including lignin, flavonoids, lignans, phenylpropanoid esters, hydroxycinnamic acid amides, and sporopollenin. Recent studies have revealed that many factors participate in the regulation of phenylpropanoid metabolism, and modulate phenylpropanoid homeostasis when plants undergo successive developmental processes and are subjected to stressful environments. In this review, we summarize recent progress on elucidating the contribution of phenylpropanoid metabolism to the coordination of plant development and plant-environment interaction, and metabolic flux redirection among diverse metabolic routes. In addition, our review focuses on the regulation of phenylpropanoid metabolism at the transcriptional, post-transcriptional, post-translational, and epigenetic levels, and in response to phytohormones and biotic and abiotic stresses.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/jipb.13054

Contribution of phenylpropanoid metabolism to plant development and plant-environment interactions.

Phenylpropanoids are a large class of plant secondary metabolites derived from aromatic amino acids phenylalanine in most plants or tyrosine in partial monocots. It mainly includes flavonoids, mono...

Biosynthesis and Regulation of Phenylpropanoids in Plants

From an evolutionary perspective, the emergence of the sophisticated chemical scaffolds of flavonoid molecules represents a key step in the colonization of Earth’s terrestrial environment by vascular plants nearly 500 million years ago. The subsequent evolution of flavonoids through recruitment and modification of ancestors involved in primary metabolism has allowed vascular plants to cope with pathogen invasion and damaging UV light. The functional properties of flavonoids as a unique combination of different classes of compounds vary significantly depending on the demands of their local real estate. Apart from geographical location, the composition of flavonoids is largely dependent on the plant species, their developmental stage, tissue type, subcellular localization, and key ecological influences of both biotic and abiotic origin. Molecular and metabolic cross-talk between flavonoid and other pathways as a result of the re-direction of intermediate molecules have been well investigated. This metabolic plasticity is a key factor in plant adaptive strength and is of paramount importance for early land plants adaptation to their local ecosystems. In human and animal health the biological and pharmacological activities of flavonoids have been investigated in great depth and have shown a wide range of anti-inflammatory, anti-oxidant, anti-microbial and anti-cancer properties. In this paper we review the application of advanced gene technologies for targeted reprogramming of the flavonoid pathway in plants to understand its molecular functions and explore opportunities for major improvements in forage plants enhancing animal health and production.

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Flavonoids: a metabolic network mediating plants adaptation to their real estate

MYB transcription factors, active players in abiotic stress signaling.

DNA binding with One Finger (DOF) transcription factors are involved in multiple aspects of plant growth and development but their precise roles in abiotic stress tolerance are largely unknown. Here we report a group of five tomato DOF genes, homologous to Arabidopsis Cycling DOF Factors (CDFs), that function as transcriptional regulators involved in responses to drought and salt stress and flowering-time control in a gene-specific manner. SlCDF1–5 are nuclear proteins that display specific binding with different affinities to canonical DNA target sequences and present diverse transcriptional activation capacities in vivo. SlCDF1–5 genes exhibited distinct diurnal expression patterns and were differentially induced in response to osmotic, salt, heat, and low-temperature stresses. Arabidopsis plants overexpressing SlCDF1 or SlCDF3 showed increased drought and salt tolerance. In addition, the expression of various stress-responsive genes, such as COR15, RD29A, and RD10, were differentially activated in the overexpressing lines. Interestingly, overexpression in Arabidopsis of SlCDF3 but not SlCDF1 promotes late flowering through modulation of the expression of flowering control genes such as CO and FT. Overall, our data connect SlCDFs to undescribed functions related to abiotic stress tolerance and flowering time through the regulation of specific target genes and an increase in particular metabolites.

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Characterization of tomato Cycling Dof Factors reveals conserved and new functions in the control of flowering time and abiotic stress responses

The phenylpropanoid metabolic pathway provides a wide variety of essential compounds for plants. Together with sinapate esters, in Brassicaceae species, flavonoids play an important role in protecting plants against UV irradiation. In this work we have characterized Arabidopsis thaliana AtMYB7, the closest homolog of AtMYB4 and AtMYB32, described as repressors of different branches of phenylpropanoid metabolism. The characterization of atmyb7 plants revealed an induction of several genes involved in flavonol biosynthesis and an increased amount of these compounds. In addition, AtMYB7 gene expression is repressed by AtMYB4. As a consequence, the atmyb4 mutant plants present a reduction of flavonol contents, indicating once more that AtMYB7 represses flavonol biosynthesis. Our results also show that AtMYB7 gene expression is induced by salt stress. Induction assays indicated that AtMYB7 represses several genes of the flavonoid pathway, DFR and UGT being early targets of this transcription factor. The results obtained indicate that AtMYB7 is a repressor of flavonol biosynthesis and also led us to propose AtMYB4 and AtMYB7 as part of the regulatory mechanism controlling the balance of the main A. thaliana UV-sunscreens.

/pdf/atmyb7-a-new-player-in-the-regulation-of-uv-sunscreens-in-41s5em4npa.pdf

AtMYB7, a New Player in the Regulation of UV-Sunscreens in Arabidopsis thaliana

We gratefully acknowledge funding through grants from Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria (INIA; project numbers: 2009-0004-C01, 2012-0008-C01) and the Spanish Ministry of Science and Innovation (project number: BIO2010-14871 and ERA-NET GEN2006-27772-C2-2). Additionally, we are grateful for the protocol described by Lakhssassi et al. (2012).

/pdf/salinity-assay-in-arabidopsis-3yfmg97yz5.pdf

Salinity assay in Arabidopsis

We gratefully acknowledge funding through grants from the Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria (INIA; project numbers: 2009-0004-C01, 2012-0008-C01) and the Spanish Ministry of Science and Innovation (project numbers: BIO2010-14871 and ERA-NET GEN2006-27772-C2-2).

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Pedro Fernández-Nohales

Papers

Characterization of tomato Cycling Dof Factors reveals conserved and new functions in the control of flowering time and abiotic stress responses

AtMYB7, a New Player in the Regulation of UV-Sunscreens in Arabidopsis thaliana

Salinity assay in Arabidopsis

Salinity Assay in Tomato