The variations in the nuclear proteome reveal new transcription factors and mechanisms involved in UV stress response in Pinus radiata

The Integration of Data from Different Long-Read Sequencing Platforms Enhances Proteoform Characterization in Arabidopsis

The increasing availability of massive omics data requires improving the quality of reference databases and their annotations. The combination of full-length isoform sequencing (Iso-Seq) with short-read transcriptomics and proteomics has been successfully used for increasing proteoform characterization, which is a main ongoing goal in biology. However, the potential of including Oxford Nanopore Technologies Direct RNA Sequencing (ONT-DRS) data has not been explored. In this paper, we analyzed the impact of combining Iso-Seq- and ONT-DRS-derived data on the identification of proteoforms in Arabidopsis MS proteomics data. To this end, we selected a proteomics dataset corresponding to senescent leaves and we performed protein searches using three different protein databases: AtRTD2 and AtRTD3, built from the homonymous transcriptomes, regarded as the most complete and up-to-date available for the species; and a custom hybrid database combining AtRTD3 with publicly available ONT-DRS transcriptomics data generated from Arabidopsis leaves. Our results show that the inclusion and combination of long-read sequencing data from Iso-Seq and ONT-DRS into a proteogenomic workflow enhances proteoform characterization and discovery in bottom-up proteomics studies. This represents a great opportunity to further investigate biological systems at an unprecedented scale, although it brings challenges to current protein searching algorithms.

Proteomics research in forest trees: A 2012-2022 update

This review is a compilation of proteomic studies on forest tree species published in the last decade (2012-2022), mostly focused on the most investigated species, including Eucalyptus, Pinus, and Quercus. Improvements in equipment, platforms, and methods in addition to the increasing availability of genomic data have favored the biological knowledge of these species at the molecular, organismal, and community levels. Integration of proteomics with physiological, biochemical and other large-scale omics in the direction of the Systems Biology, will provide a comprehensive understanding of different biological processes, from growth and development to responses to biotic and abiotic stresses. As main issue we envisage that proteomics in long-living plants will thrive light on the plant responses and resilience to global climate change, contributing to climate mitigation strategies and molecular breeding programs. Proteomics not only will provide a molecular knowledge of the mechanisms of resilience to either biotic or abiotic stresses, but also will allow the identification on key gene products and its interaction. Proteomics research has also a translational character being applied to the characterization of the variability and biodiversity, as well as to wood and non-wood derived products, traceability, allergen and bioactive peptides identification, among others. Even thought, the full potential of proteomics is far from being fully exploited in forest tree research, with PTMs and interactomics being reserved to plant model systems. The most outstanding achievements in forest tree proteomics in the last decade as well as prospects are discussed.

Targeted Mass Spectrometry Analysis of Protein Phosphorylation by Selected Ion Monitoring Coupled to Parallel Reaction Monitoring (tSIM/PRM)

Recent developments in targeted mass spectrometry-based proteomics have provided new methodological solutions for accurate and quantitative analysis of proteins and their posttranslational control, which has significantly advanced our understanding of stress responses in different plant species. Instrumentation allowing high-resolution, accurate-mass (HR/AM) analysis has provided new acquisition strategies for targeted quantitative proteomic analysis by targeted selected ion monitoring (tSIM) and parallel reaction monitoring (PRM). Here we report a sensitive and accurate method for targeted analysis of protein phosphorylation by tSIM coupled to PRM (tSIM/PRM). The tSIM/PRM method takes advantage of HR/AM mass spectrometers and benefits from the combination of highly sensitive precursor ion quantification by tSIM and highly confident peptide identification by spectral library matching in PRM. The detailed protocol describes tSIM/PRM analysis of Arabidopsis thaliana foliar proteins, from the building of a spectral library to sample preparation, mass spectrometry, and data analysis, and provides a methodological approach for specifying the molecular mechanisms of interest.

Subcellular Proteomics in Conifers: Purification of Nuclei and Chloroplast Proteomes

The complexity of the plant cell proteome, exhibiting thousands of proteins whose abundance varies in several orders of magnitude, makes impossible to cover most of the plant proteins using standard shotgun-based approaches. Despite this general description of plant proteomes, the complexity is not a big issue (current protocols and instrumentation allow for the identification of several thousand proteins per injection), low or medium abundant proteins cannot be detected most of times, being necessary to fraction or perform targeted analyses in order to detect and quantify them. Among fractioning choices, cell fractioning in its different organelles is a good strategy for gaining not only a deeper coverage of the proteome but also the basis for understanding organelle function, protein dynamics, and trafficking within the cell, as nuclear and chloroplast communication. This approach is used routinely in many labs working with model species; however, the available protocols focusing on tree species are scarce. In this chapter, we provide a simple but robust protocol for isolating nuclei and chloroplasts in pine needles that is fully compatible with later mass spectrometry-based proteome analysis.

Mass spectrometry-based forest tree metabolomics

Research in forest tree species has advanced slowly when compared with other agricultural crops and model organisms, mainly due to the long-life cycles, large genome sizes, and lack of genomic tools. Additionally, trees are complex matrices, and the presence of interferents (e.g., oleoresins and cellulose) challenges the analysis of tree tissues with mass spectrometry (MS)-based analytical platforms. In this review, advances in MS-based forest tree metabolomics are discussed. Given their economic and ecological significance, particular focus is given to Pinus, Quercus, and Eucalyptus forest tree species to better understand their metabolite responses to abiotic and biotic stresses in the current climate change scenario. Furthermore, MS-based metabolomics technologies produce large and complex datasets that require expertize to adequately manage, process, analyze, and store the data in dedicated repositories. To ensure that the full potential of forest tree metabolomics data are translated into new knowledge, these data should comply with the FAIR principles (i.e., Findable, Accessible, Interoperable, and Re-usable). It is essential that adequate standards are implemented to annotate metadata from forest tree metabolomics studies as is already required by many science and governmental agencies and some major scientific publishers. © 2019 John Wiley & Sons Ltd. Mass Spec Rev 40:126-157, 2021.

Integrative analysis of the nuclear proteome in Pinus radiata reveals thermopriming coupled to epigenetic regulation

Despite it being an important issue in the context of climate change, for most plant species it is not currently known how abiotic stresses affect nuclear proteomes and mediate memory effects. This study examines how Pinus radiata nuclei respond, adapt, 'remember', and 'learn' from heat stress. Seedlings were heat-stressed at 45 °C for 10 d and then allowed to recover. Nuclear proteins were isolated and quantified by nLC-MS/MS, the dynamics of tissue DNA methylation were examined, and the potential acquired memory was analysed in recovered plants. In an additional experiment, the expression of key gene genes was also quantified. Specific nuclear heat-responsive proteins were identified, and their biological roles were evaluated using a systems biology approach. In addition to heat-shock proteins, several clusters involved in regulation processes were discovered, such as epigenomic-driven gene regulation, some transcription factors, and a variety of RNA-associated functions. Nuclei exhibited differential proteome profiles across the phases of the experiment, with histone H2A and methyl cycle enzymes in particular being accumulated in the recovery step. A thermopriming effect was possibly linked to H2A abundance and over-accumulation of spliceosome elements in recovered P. radiata plants. The results suggest that epigenetic mechanisms play a key role in heat-stress tolerance and priming mechanisms.

Proteomics, Holm Oak (Quercus ilex L.) and Other Recalcitrant and Orphan Forest Tree Species: How do They See Each Other?

Proteomics has had a big impact on plant biology, considered as a valuable tool for several forest species, such as Quercus, Pines, Poplars, and Eucalyptus. This review assesses the potential and limitations of the proteomics approaches and is focused on Quercus ilex as a model species and other forest tree species. Proteomics has been used with Q. ilex since 2003 with the main aim of examining natural variability, developmental processes, and responses to biotic and abiotic stresses as in other species of the genus Quercus or Pinus. As with the progress in techniques in proteomics in other plant species, the research in Q. ilex moved from 2-DE based strategy to the latest gel-free shotgun workflows. Experimental design, protein extraction, mass spectrometric analysis, confidence levels of qualitative and quantitative proteomics data, and their interpretation are a true challenge with relation to forest tree species due to their extreme orphan and recalcitrant (non-orthodox) nature. Implementing a systems biology approach, it is time to validate proteomics data using complementary techniques and integrate it with the -omics and classical approaches. The full potential of the protein field in plant research is quite far from being entirely exploited. However, despite the methodological limitations present in proteomics, there is no doubt that this discipline has contributed to deeper knowledge of plant biology and, currently, is increasingly employed for translational purposes.

Subcellular Proteomics: Application to Elucidation of Flooding-Response Mechanisms in Soybean

Soybean, which is rich in protein and oil, is cultivated in several climatic zones; however, its growth is markedly decreased by flooding. Proteomics is a useful tool for understanding the flooding-response mechanism in soybean. Subcellular proteomics has the potential to elucidate localized cellular responses and investigate communications among subcellular components during plant growth and during stress. Under flooding, proteins related to signaling, stress and the antioxidative system are increased in the plasma membrane; scavenging enzymes for reactive-oxygen species are suppressed in the cell wall; protein translation is suppressed through inhibition of proteins related to preribosome biogenesis and mRNA processing in the nucleus; levels of proteins involved in the electron transport chain are reduced in the mitochondrion; and levels of proteins related to protein folding are decreased in the endoplasmic reticulum. This review discusses the advantages of a gel-free/label-free proteomic technique and methods of plant subcellular purification. It also summarizes cellular events in soybean under flooding and discusses future prospects for generation of flooding-tolerant soybean.

Sma3s: A universal tool for easy functional annotation of proteomes and transcriptomes

The current cheapening of next-generation sequencing has led to an enormous growth in the number of sequenced genomes and transcriptomes, allowing wet labs to get the sequences from their organisms of study. To make the most of these data, one of the first things that should be done is the functional annotation of the protein-coding genes. But it used to be a slow and tedious step that can involve the characterization of thousands of sequences. Sma3s is an accurate computational tool for annotating proteins in an unattended way. Now, we have developed a completely new version, which includes functionalities that will be of utility for fundamental and applied science. Currently, the results provide functional categories such as biological processes, which become useful for both characterizing particular sequence datasets and comparing results from different projects. But one of the most important implemented innovations is that it has now low computational requirements, and the complete annotation of a simple proteome or transcriptome usually takes around 24 hours in a personal computer. Sma3s has been tested with a large amount of complete proteomes and transcriptomes, and it has demonstrated its potential in health science and other specific projects.

System-wide analysis of short-term response to high temperature in Pinus radiata

Pinus radiata seedlings, the most widely planted pine species in the world, were exposed to temperatures within a range mimicking future scenarios based on current models of heat increase. The short-term heat response in P. radiata was studied in detail by exploring the metabolome, proteome and targeted transcriptome. The use of complementary mass spectrometry techniques, GC-MS and LC-Orbitrap-MS, together with novel bioinformatics tools allowed the reliable quantification of 2,075 metabolites and 901 protein groups. Integrative analyses of different functional levels and plant physiological status revealed a complex molecular interaction network of positive and negative correlations between proteins and metabolites involved in short-term heat response, including three main physiological functions as: 1) A hormone subnetwork, where fatty acids, flavonoids and hormones presented a key role; 2) An oxidoreductase subnetwork, including several dehydrogenase and peroxidase proteins; and 3) A heat shock protein subnetwork, with numerous proteins that contain a HSP20 domain, all of which were overexpressed at the transcriptional level. Integrated analysis pinpointed the basic mechanisms underlying the short-term physiological reaction of P. radiata during heat response. This approach was feasible in forest species and unmasked two novel candidate biomarkers of heat resistance, PHO1 and TRANSCRIPTION FACTOR APFI, and a MITOCHONDRIAL SMALL HEAT SHOCK PROTEIN, for use in future breeding programs.

Integrated Physiological, Proteomic, and Metabolomic Analysis of Ultra Violet (UV) Stress Responses and Adaptation Mechanisms in Pinus radiata

Globally expected changes in environmental conditions, especially the increase of UV irradiation, necessitate extending our knowledge of the mechanisms mediating tree species adaptation to this stress. This is crucial for designing new strategies to maintain future forest productivity. Studies focused on environmentally realistic dosages of UV irradiation in forest species are scarce. Pinus spp. are commercially relevant trees and not much is known about their adaptation to UV. In this work, UV treatment and recovery of Pinus radiata plants with dosages mimicking future scenarios, based on current models of UV radiation, were performed in a time-dependent manner. The combined metabolome and proteome analysis were complemented with measurements of + physiological parameters and gene expression. Sparse PLS analysis revealed complex molecular interaction networks of molecular and physiological data. Early responses prevented phototoxicity by reducing photosystem activity and the electron transfer chain together with the accumulation of photoprotectors and photorespiration. Apart from the reduction in photosynthesis as consequence of the direct UV damage on the photosystems, the primary metabolism was rearranged to deal with the oxidative stress while minimizing ROS production. New protein kinases and proteases related to signaling, coordination, and regulation of UV stress responses were revealed. All these processes demonstrate a complex molecular interaction network extending the current knowledge on UV-stress adaptation in pine.

Dataset of UV induced changes in nuclear proteome obtained by GeLC-Orbitrap/MS in Pinus radiata needles

Although responses to UV stress have been characterised at system and cellular levels, the dynamics of the nuclear proteome triggered in this situation are still unknown, despite its essential role in regulating gene expression and in last term plant physiology. To fill this gap, we characterised the variations in the nuclear proteome after 2 h and 16 h (8 h/day) of UV irradiation by using state-of-the-art mass spectrometry-based shotgun proteomics methods combined with novel bioinformatics workflows that were employed in the manuscript entitled "The variations in the nuclear proteome reveal new transcription factors and mechanisms involved in UV stress response in Pinus radiata" (Pascual et al., 2016) [1]. We employed in-gel digestion followed by a 120 min gradient prior to MS analysis. Data was processed following two approaches: a database dependent employing the SEQUEST algorithm and custom databases, and a database independent by mass accuracy precursor alignment (MAPA). 388 proteins were identified by SEQUEST search and 9094 m/z were quantified by MAPA. Significant m/z were de novo sequenced using the Novor algorithm. We present here the complete datasets and the analysis workflow.