Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes

The mRNA mobileome: challenges and opportunities for deciphering signals from the noise

Organismal communication entails encoding a message that is sent over space or time to a recipient cell, where that message is decoded to activate a downstream response. Defining what qualifies as a functional signal is essential for understanding intercellular communication. In this review, we delve into what is known and unknown in the field of long-distance messenger RNA (mRNA) movement and draw inspiration from the field of information theory to provide a perspective on what defines a functional signaling molecule. Although numerous studies support the long-distance movement of hundreds to thousands of mRNAs through the plant vascular system, only a small handful of these transcripts have been associated with signaling functions. Deciphering whether mobile mRNAs generally serve a role in plant communication has been challenging, due to our current lack of understanding regarding the factors that influence mRNA mobility. Further insight into unsolved questions regarding the nature of mobile mRNAs could provide an understanding of the signaling potential of these macromolecules.

Combining BN-PAGE and microscopy techniques to investigate pigment-protein complexes and plastid transitions in citrus fruit

BACKGROUND

Chlorophyll and carotenoids, the most widely distributed lipophilic pigments in plants, contribute to fruit coloration during development and ripening. These pigments are assembled with pigment-protein complexes localized at plastid membrane. Pigment-protein complexes are essential for multiple cellular processes, however, their identity and composition in fruit have yet to be characterized.

RESULTS

By using BN-PAGE technique in combination with microscopy, we studied pigment-protein complexes and plastid transformation in the purified plastids from the exocarp of citrus fruit. The discontinuous sucrose gradient centrifugation was used to isolate total plastids from kumquat fruit, and the purity of isolated plastids was assessed by microscopy observation and western blot analysis. The isolated plastids at different coloring stages were subjected to pigment autofluorescence observation, western blot, two-dimensional electrophoresis analysis and BN-PAGE assessment. Our results demonstrated that (i) chloroplasts differentiate into chromoplasts during fruit coloring, and this differentiation is accompanied with a decrease in the chlorophyll/carotenoid ratio; (ii) BN-PAGE analysis reveals the profiles of macromolecular protein complexes among different types of plastids in citrus fruit; and (iii) the degradation rate of chlorophyll-protein complexes varies during the transition from chloroplasts to chromoplasts, with the stability generally following the order of LHCII > PS II core > LHC I > PS I core.

CONCLUSIONS

Our optimized methods for both plastid separation and BN-PAGE assessment provide an opportunity for developing a better understanding of pigment-protein complexes and plastid transitions in plant fruit. These attempts also have the potential for expanding our knowledge on the sub-cellular level synchronism of protein changes and pigment metabolism during the transition from chloroplasts to chromoplasts.

Intrinsically disordered plant protein PARCL colocalizes with RNA in phase-separated condensates whose formation can be regulated by mutating the PLD

In higher plants, long-distance RNA transport via the phloem is crucial for communication between distant plant tissues to align development with stress responses and reproduction. Several recent studies suggest that specific RNAs are among the potential long-distance information transmitters. However, it is yet not well understood how these RNAs enter the phloem stream, how they are transported, and how they are released at their destination. It was proposed that phloem RNA-binding proteins facilitate RNA translocation. In the present study, we characterized two orthologs of the phloem-associated RNA chaperone-like (PARCL) protein from Arabidopsis thaliana and Brassica napus at functional and structural levels. Microscale thermophoresis showed that these phloem-abundant proteins can bind a broad spectrum of RNAs and show RNA chaperone activity in FRET-based in vitro assays. Our SAXS experiments revealed a high degree of disorder, typical for RNA-binding proteins. In agroinfiltrated tobacco plants, eYFP-PARCL proteins mainly accumulated in nuclei and nucleoli and formed cytosolic and nuclear condensates. We found that formation of these condensates was impaired by tyrosine-to-glutamate mutations in the predicted prion-like domain (PLD), while C-terminal serine-to-glutamate mutations did not affect condensation but reduced RNA binding and chaperone activity. Furthermore, our in vitro experiments confirmed phase separation of PARCL and colocalization of RNA with the condensates, while mutation as well as phosphorylation of the PLD reduced phase separation. Together, our results suggest that RNA binding and condensate formation of PARCL can be regulated independently by modification of the C-terminus and/or the PLD.

Probing the Metabolic Landscape of Plant Vascular Bundles by Infrared Fingerprint Analysis, Imaging and Mass Spectrometry

Fingerprint analysis is a common technique in forensic and criminal investigations. Similar techniques exist in the field of infrared spectroscopy to identify biomolecules according to their characteristic spectral fingerprint features. These unique markers are located in a wavenumber range from 1800 to 600 cm-1 in the mid infrared region. Here, a novel bioanalytical concept of correlating these spectral features with corresponding mass spectrometry datasets to unravel metabolic clusters within complex plant tissues was applied. As proof of concept, vascular bundles of oilseed rape (Brassica napus) were investigated, one of the most important and widely cultivated temperate zone oilseed crops. The link between mass spectrometry data and spectral data identified features that co-aligned within both datasets. Regions of origin were then detected by searching for these features in hyperspectral images of plant tissues. This approach, based on co-alignment and co-localization, finally enabled the detection of eight distinct metabolic clusters, reflecting functional and structural arrangements within the vascular bundle. The proposed analytical concept may assist future synergistic research approaches and may lead to biotechnological innovations with regard to crop yield and sustainability.

Phloem exudate metabolic content reflects the response to water-deficit stress in pea plants (Pisum sativum L.)

Drought stress impacts the quality and yield of Pisum sativum. Here, we show how short periods of limited water availability during the vegetative stage of pea alters phloem sap content and how these changes are connected to strategies used by plants to cope with water deficit. We have investigated the metabolic content of phloem sap exudates and explored how this reflects P. sativum physiological and developmental responses to drought. Our data show that drought is accompanied by phloem-mediated redirection of the components that are necessary for cellular respiration and the proper maintenance of carbon/nitrogen balance during stress. The metabolic content of phloem sap reveals a shift from anabolic to catabolic processes as well as the developmental plasticity of P. sativum plants subjected to drought. Our study underlines the importance of phloem-mediated transport for plant adaptation to unfavourable environmental conditions. We also show that phloem exudate analysis can be used as a useful proxy to study stress responses in plants. We propose that the decrease in oleic acid content within phloem sap could be considered as a potential marker of early signalling events mediating drought response.

Unraveling the Roles of Vascular Proteins Using Proteomics

Vascular bundles play important roles in transporting nutrients, growth signals, amino acids, and proteins between aerial and underground tissues. In order to understand these sophisticated processes, a comprehensive analysis of the roles of the components located in the vascular tissues is required. A great deal of data has been obtained from proteomic analyses of vascular tissues in plants, which mainly aim to identify the proteins moving through the vascular tissues. Here, different aspects of the phloem and xylem proteins are reviewed, including their collection methods, and their main biological roles in growth, and biotic and abiotic stress responses. The study of vascular proteomics shows great potential to contribute to our understanding of the biological mechanisms related to development and defense in plants.