Phytochrome A increases tolerance to high evaporative demand

IFEVA-CONICET, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina IBAM-CONICET, Facultad de Ciencias Agrarias, Universidad Nacional de Cuyo, Mendoza, Argentina Instituto de Ciencias Básicas, Universidad Nacional de Cuyo, Mendoza, Argentina Laboratorio de Anatomía Vegetal, Cátedra de Botánica Agrícola, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina.
Physiologia Plantarum (Impact Factor: 3.14). 10/2012; 146(2):228. DOI: 10.1111/j.1399-3054.2012.01625.x


Stresses resulting from high transpiration demand induce adjustments in plants that lead to reductions of water loss. These adjustments, including changes in water absorption, transport and/or loss by transpiration, are crucial to normal plant development. Tomato wild type (WT) and phytochrome A mutant plants, fri1-1, were exposed to either low or high transpiration demand conditions and several morphological and physiological changes were measured during stressing conditions. Mutant plants rapidly wilted compared to WT plants after exposure to high evaporative demand. Root size and hydraulic conductivity did not show significant differences between genotypes, suggesting that water absorption and transport through this organ could not explain the observed phenotype. Moreover, stomata density was similar between genotypes, whereas transpiration and stomata conductance were both lower in mutant than in wild type plants. This was accompanied by a lower stem specific hydraulic conductivity in mutant plants than in wild type, which was associated to smaller xylem vessel number and transversal area in fri1-1 plants, producing a reduction in water supply to the leaves, rapidly reaching wilting under high evaporative demand. Phytochrome A signaling might facilitate the adjustment to environments differing widely in water evaporative demand in part through the modulation of xylem dimensions.

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Available from: Gabriela Auge
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    • "The mechanisms by which phytochrome influences water economy may be more or less complicated (Boccalandro et al., 2009; González et al., 2012; Sokolskaya et al., 2003). Some recent reports show that the phytochrome increases tolerance to high evaporative demand (Auge et al., 2012) and that phytochromes phyA and phyB can modulate drought stress responses (D'Amico-Damiāo et al., 2015). CONCLUSIONS 1. Direct solar irradiance in the far-red range depends strongly on atmospheric water vapour. "
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    ABSTRACT: ABSTRACT. It is commonly accepted that an important role of phytochrome lies in signaling the proximity of competing plants. However, not all photoresponses conveyed by the phytochrome can be explained by the competition only. Because a better description of the natural variability of solar spectral irradiance is necessary to recognize the other roles of the phytochrome, long-lasting spectroradiometric measurements have been performed. Special attention has been paid to the relations between the far red and red bands of solar spectrum, which have an impact on the phytochrome. The effect of atmospheric moisture on the far red irradiance (attenuated in the 720 nm band of water vapor absorption) is described. The far red irradiance, active in the ”high irradiance response” of the phytochrome, and the red/far-red ratio, important for the “low fluence response”, may vary very strongly relative to the atmospheric moisture. Together with other facts known from photophysiology, the results of the measurements enabled us to formulate a thesis that the phytochrome monitors the amount of water vapor and opens appropriate metabolic pathways to cope with the danger of drought. The recognition of this novel role of the phytochrome might broaden the knowledge in the area of plant photomorphogenesis and ecology. K e y w o r d s: Atmospheric absorption, far red irradiation, high irradiance response, phytochrome, precipitable water
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    • "However, whether the " phyA–promoter association " model is a universal mechanism for gene regulation throughout the entire genome of Arabidopsis, and whether FR influences multiple biological processes beyond anthocyanin accumulation, remain to be determined. Interestingly, recent reports have identified crosstalk networks involving phyA and numerous internal and external stimuli, such as brassinosteroid, auxin, and various stresses resulting from water loss or wounds (Robson et al., 2010; Liu et al., 2011; Auge et al., 2012; Sandhu et al., 2012). Moreover, abscisic acid (ABA) signaling interferes with phyA-dependent seed germination (Lee et al., 2012). "
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    ABSTRACT: The far-red light (FR) photoreceptor phytochrome A (phyA) contains no DNA binding domain but associates with the CHALCONE SYNTHASE promoter through its chaperone FAR-RED ELONGATED HYPOCOTYL1 and transcription factors. Here, we performed a genome-wide identification of phyA targets using a combination of phyA chromatin immunoprecipitation and RNA sequencing methods in Arabidopsis thaliana. Our results indicate that phyA signaling widely affects gene promoters involved in multiple FR-modulated aspects of plant growth. Furthermore, we observed an enrichment of hormone- and stress-responsive elements in the phyA direct target promoters, indicating that a much broader than expected range of transcription factors is involved in the phyA signaling pathway. To verify our hypothesis that phyA regulates genes other than light-responsive ones through the interaction with corresponding transcription factors, we examined the action of phyA on one of its direct target genes, NAC019, which encodes an abscisic acid-dependent transcription factor. The phyA signaling cascade not only targets two G-boxes on the NAC019 promoter for subsequent transcriptional regulation but also positively coordinates with the abscisic acid signaling response for root elongation inhibition under FR. Our study provides new insight into how plants rapidly fine-tune their growth strategy upon changes in the light environment by escorting photoreceptors to the promoters of hormone- or stress-responsive genes for individualized modulation.
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    ABSTRACT: The dynamic light environment of vegetation canopies is perceived by phytochromes, cryptochromes, phototropins, and UV RESISTANCE LOCUS 8 (UVR8). These receptors control avoidance responses to preclude exposure to limiting or excessive light and acclimation responses to cope with conditions that cannot be avoided. The low red/far-red ratios of shade light reduce phytochrome B activity, which allows PHYTOCHROME INTERACTING FACTORS (PIFs) to directly activate the transcription of auxin-synthesis genes, leading to shade-avoidance responses. Direct PIF interaction with DELLA proteins links gibberellin and brassinosteroid signaling to shade avoidance. Shade avoidance also requires CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1), a target of cryptochromes, phytochromes, and UVR8. Multiple regulatory loops and the input of the circadian clock create a complex network able to respond even to subtle threats of competition with neighbors while still compensating for major environmental fluctuations such as the day-night cycles. Expected final online publication date for the Annual Review of Plant Biology Volume 64 is April 29, 2013. Please see for revised estimates.
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