Journal of Experimental Botany最新文献

The UV RESISTANCE LOCUS 8 (UVR8) photoreceptor mediates many plant responses to UV-B and short wavelength UV-A light. UVR8 functions through interactions with other proteins which lead to extensive changes in gene expression. Interactions with particular proteins determine the nature of the response to UV-B. It is therefore important to understand the molecular basis of these interactions: how are different proteins able to bind to UVR8 and how is differential binding regulated? This concise review highlights recent developments in addressing these questions. Key advances are discussed with regard to: identification of proteins that interact with UVR8; the mechanism of UVR8 accumulation in the nucleus; the photoactivation of UVR8 monomer; the structural basis of interaction between UVR8 and CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) proteins; and the role of UVR8 phosphorylation in modulating interactions and responses to UV-B. Nevertheless, much remains to be understood, and the need to extend future research to the growing list of interactors is emphasized.

We employed hyperspectral imaging to detect chloroplast positioning and assess its influence on common vegetation indices. In low blue light, chloroplasts move to cell walls perpendicular to the direction of the incident light. In high blue light, chloroplasts exhibit the avoidance response, moving to cell walls parallel to the light direction. Irradiation with high light resulted in significant changes in leaf reflectance and the shape of the reflectance spectrum. Using mutants with disrupted chloroplast movements, we found that blue light-induced changes in the reflectance spectrum are mostly due to chloroplast relocations. We trained machine learning methods in the classification of leaves according to the chloroplast positioning, based on the reflectance spectra. The convolutional network showed low levels of misclassification of leaves irradiated with high light even when different species were used for training and testing, suggesting that reflectance spectra may be used to detect chloroplast avoidance in heterogeneous vegetation. We also examined the correlation between chloroplast positioning and values of indices of normalized-difference type for various combinations of wavelengths and identified an index sensitive to chloroplast positioning. We found that values of some of the vegetation indices, including those sensitive to the carotenoid levels, may be altered due to chloroplast rearrangements.

Chilling stress restricts the geographical distribution of rice and severely impacts its growth and development, ultimately reducing both yield and quality. The plant hormone ethylene is involved in plant stress responses; however, its role in rice chilling tolerance has not been thoroughly explored. This study reveals that ethylene negatively regulates chilling tolerance in rice by antagonizing the chilling tolerance-promoting effects of abscisic acid (ABA). Treatment with ethylene or its biosynthetic precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), results in a reduced survival rate after chilling and delayed stomatal closure in response to chilling. There are two ethylene signaling-related Raf-like protein kinases, OsCTR1 and OsCTR2, which have overlapping functions in ethylene signaling; their loss-of-function mutants exhibit constitutive ethylene responses. The ctr1 ctr2 double mutant displays lower survival rates and slower stomatal closure under chilling stress compared to the wild type. In contrast, ABA treatment significantly enhances the survival rate of the wild type under chilling stress and promotes stomatal closure in response to chilling. Furthermore, ethylene inhibits the effects of ABA on chilling tolerance and stomatal closure. The ctr1 ctr2 double mutant fails to respond to external ABA treatment regarding stomatal closure and increased survival rate under chilling stress. In conclusion, our findings suggest that ethylene negatively regulates chilling tolerance in rice by inhibiting ABA-induced stomatal closure through the action of OsCTR1 and OsCTR2.

Stress granules (SGs) are cytoplasmic structures that emerge in response to unfavorable environmental conditions. The mechanisms governing the accumulation of transcripts in SGs are only partially understood. Despite the recognized role of N6-methyladenosine (m6A) in plant transcriptome regulation, its impact on SGs' composition and assembly remains elusive. In Lupinus angustifolius, SGs display a distinctive bi-zonal structure comprising of a ring and a central area with differences in ultrastructure and composition. Subsequent to the transcriptome analysis, specific mRNA were chosen to investigate their localization within SGs and assess m6A levels. Transcripts of hypoxia-responsive genes (ADH1 and HUP7) showed significantly lower levels of m6A compared to housekeeping genes, but only ADH1 was absent in SGs. HUP7 mRNA, characterized by a low quantity of m6A, is present both in the SGs and cytoplasm, probably due to extremely high expression level. The m6A was observed only during the assembly of SGs. In mutants of Arabidopsis thaliana with reduced levels of m6A, ECT2 (reader of m6A) was not observed in SGs, and poly(A) RNA levels and the number of SGs were reduced. In summary, our findings demonstrate a limited impact of m6A modification on SGs assembly. However, the interplay between m6A modification and the overall transcript quantity in the cytoplasm appears to play a regulatory role in mRNA partitioning and assembly of SGs.

Grapevine leafroll disease is the most damaging viral disease afflicting global grape and wine production. Of the five viruses likely associated with the disease, grapevine leafroll-associated virus 3 (GLRaV3) is believed to be the predominant agent, albeit its role as the causal agent has remained uncertain. GLRaV3 (species Ampelovirus trivitis, genus Ampelovirus, family Closteroviridae) has the third largest single-stranded, positive-sense RNA genome among plant viruses at ~18.5 kb, only surpassed by two other members of the family Closteroviridae, citrus tristeza virus, and GLRaV1. GLRaV3 is unique among plant viruses in several ways including the size of its genome, the long non-coding regions, and its association with the outer mitochondrial membrane for viral replication. Unfortunately, our understanding of the molecular mechanisms governing GLRaV3 genome replication, gene expression and virus-host interactions is poor due to many factors, including the unavailability of infectious cDNA clones and effective experimental system to initiate grapevine infection with viral clones until recently. In this review, we capture some recent advances in GLRaV3 research towards the establishment of infectious clones, grapevine inoculation systems, as well as approaches towards elucidating the function of GLRaV3-encoded proteins. We also present a working model to explain GLRaV3 pathogenesis.

Asynchronicity causes metabolic chimerism in usual grapevine phenological stages, calling for a revisit of berry development at the individual fruit scale. To reveal the dynamics of metabolite composition in grapevine berries without phenological a priori, a dataset of 9,256 ions was obtained on 125 fruits at different stages by non-targeted ultra-performance liquid chromatography coupled to high-resolution mass spectrometry. This large metabolomic dataset was submitted to an analysis workflow combining classification and dimension reduction tools. This led to the clustering of metabolites into 12 specific kinetic patterns and a metabolome-based definition of the pericarp intrinsic clock outperforming expert timing procedures. Such increased temporal resolution enabled the identification of metabolite clusters that are annunciative of the onset of ripening, noticeably characterized by transient lipidic changes and the start of ABA accumulation. We also highlighted a cluster of stilbenes that accumulate during terminal fruit shriveling, after the arrest of phloem unloading. This non-targeted approach enables a more precise characterization of grapevine berry development through the concept of metabolomic clock. The discovery of new metabolic milestones of berry development paves the way toward a better assessment of the impact of environmental changes on the metabolism of non-climacteric fruit, in different genotypes.

The plastidial α-glucan phosphorylase (PHS1) can catalyze the elongation and degradation of glucans, but its exact physiological role in plants is not completely deciphered. A plethora of studies have indicated that PHS1 is involved in transitory starch turnover, both in photosynthetic tissues as well as reserve starch accumulation in sink organs of multiple species, by exerting its effects on the plastidial maltodextrin pools. Recent studies have also established its role in the mobilization of short maltooligosaccharides (MOSs), thereby assisting in starch granule initiation. This paper highlights our current findings from studying four constitutive double-knock out mutants related to the plastidial maltodextrin metabolism namely phs1dpe1, phs1ptst2, phs1pgm1 and phs1isa3 of Arabidopsis thaliana. Our studies have indicated different effects on carbon partitioning in these double mutants. The carbon allocation between starch and sucrose in different double mutants varied with respect to time and light conditions with significant overall changes in phs1dpe1. Furthermore, a potential time specific function of PHS1 in maltodextrin metabolism has come to light. Changes in maltodextrin turnover exerted effects on the starch granule number and size in the double mutants especially phs1dpe1. The characterized double mutants have been further assessed in terms of photosynthetic efficiency, and starch parameters such as internal structure and morphology in detail. Our results have shown that the different photosynthetic parameters in pgm1 and its corresponding double mutant were affected relative to WT and phs1. However, other double mutants were not impaired in terms of photosynthetic efficiency despite alterations in their MOS levels.

Organisms adapt to predictable environmental changes via a biological mechanism called priming. Phototropin (phot) is a plant-specific blue light photoreceptor that mediates daily light-induced responses, such as chloroplast relocation, stomatal opening, and phototropism, to optimize photosynthesis. Phot also functions as a thermosensor for chloroplast relocation that may sense daily temperature decreases at night, thereby modulating light-induced responses at dawn; however, this hypothesis has not yet been fully explored. Here, we reveal that phot mediates daily cold priming to promote stomatal opening and phototropism in Arabidopsis (Arabidopsis thaliana) under dawn-mimicking conditions. A cold pretreatment in the dark enhanced subsequent blue light-induced stomatal opening and phototropism at normal temperatures, suggesting that daily cold priming is involved in these physiological responses. Arabidopsis has two phot proteins (phot1 and phot2), and we show that phot2 clearly mediates the cold priming of stomatal opening and phototropism. Cold priming appears to be based on phot-mediated thermosensing just before dawn, which plants use to optimize their light-induced responses in anticipation of dawn.

In nature, environmental conditions strongly fluctuate, frequently subjecting plants to periods of immediate photo-oxidative stress. The small molecule ascorbate allows plants to cope with such stress conditions. Ascorbate scavenges reactive oxygen species and enables the rapid and full induction of photoprotective non-photochemical quenching (NPQ). NPQ is dependent on zeaxanthin (Zx), which requires ascorbate as the electron donor during its synthesis by the violaxanthin de-epoxidase. The VTC2 gene encodes for one of two isoforms of GDP-L-galactose phosphorylase, the rate-controlling enzyme of ascorbate biosynthesis. In the current study, by including a newly identified vtc2 allele, we found that loss of VTC2 depleted ascorbate mainly from the mature leaves and thereby limited NPQ specifically in this tissue. Growth in fluctuating light and controlled climate suppressed the slow NPQ induction phenotype of vtc2 mature leaves to some degree. This was concurrent with a constitutively higher accumulation of zeaxanthin under this condition. When plants were shifted to natural conditions, with strongly fluctuating light and temperature, the ascorbate deficient mature leaves of vtc2 bleached. Together, our results reveal developmental and environmental effects on VTC2-dependent ascorbate accumulation and function.