Comparative Proteomics of Root Apex and Root Elongation Zones Provides Insights into Molecular Mechanisms for Drought Stress and Recovery Adjustment in Switchgrass

Switchgrass plants were grown in a Sandwich tube system to induce gradual drought stress by withholding watering. After 29 days, the leaf photosynthetic rate decreased significantly, compared to the control plants which were watered regularly. The drought-treated plants recovered to the same leaf water content after three days of re-watering. The root tip (1cm basal fragment, designated as RT1 hereafter) and the elongation/maturation zone (the next upper 1 cm tissue, designated as RT2 hereafter) tissues were collected at the 29th day of drought stress treatment, (named SDT for severe drought treated), after one (D1W) and three days (D3W) of re-watering. The tandem mass tags mass spectrometry-based quantitative proteomics analysis was performed to identify the proteomes, and drought-induced differentially accumulated proteins (DAPs). From RT1 tissues, 6156, 7687, and 7699 proteins were quantified, and 296, 535, and 384 DAPs were identified in the SDT, D1W, and D3W samples, respectively. From RT2 tissues, 7382, 7255, and 6883 proteins were quantified, and 393, 587, and 321 proteins DAPs were identified in the SDT, D1W, and D3W samples. Between RT1 and RT2 tissues, very few DAPs overlapped at SDT, but the number of such proteins increased during the recovery phase. A large number of hydrophilic proteins and stress-responsive proteins were induced during SDT and remained at a higher level during the recovery stages. A large number of DAPs in RT1 tissues maintained the same expression pattern throughout drought treatment and the recovery phases. The DAPs in RT1 tissues were classified in cell proliferation, mitotic cell division, and chromatin modification, and those in RT2 were placed in cell wall remodeling and cell expansion processes. This study provided information pertaining to root zone-specific proteome changes during drought and recover phases, which will allow us to select proteins (genes) as better defined targets for developing drought tolerant plants. The mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD017441

Effect of Aluminum Treatment on Proteomes of Radicles of Seeds Derived from Al-Treated Tomato Plants

Aluminum (Al) toxicity is a major constraint to plant growth and crop yield in acid soils. Tomato cultivars are especially susceptible to excessive Al3+ accumulated in the root zone. In this study, tomato plants were grown in a hydroponic culture system supplemented with 50 µM AlK(SO4)2. Seeds harvested from Al-treated plants contained a significantly higher Al content than those grown in the control hydroponic solution. In this study, these Al-enriched tomato seeds (harvested from Al-treated tomato plants) were germinated in 50 µM AlK(SO4)2 solution in a homopiperazine-1,4-bis(2-ethanesulfonic acid) buffer (pH 4.0), and the control solution which contained the buffer only. Proteomes of radicles were analyzed quantitatively by mass spectrometry employing isobaric tags for relative and absolute quantitation (iTRAQ®). The proteins identified were assigned to molecular functional groups and cellular metabolic pathways using MapMan. Among the proteins whose abundance levels changed significantly were: a number of transcription factors; proteins regulating gene silencing and programmed cell death; proteins in primary and secondary signaling pathways, including phytohormone signaling and proteins for enhancing tolerance to abiotic and biotic stress. Among the metabolic pathways, enzymes in glycolysis and fermentation and sucrolytic pathways were repressed. Secondary metabolic pathways including the mevalonate pathway and lignin biosynthesis were induced. Biological reactions in mitochondria seem to be induced due to an increase in the abundance level of mitochondrial ribosomes and enzymes in the TCA cycle, electron transport chains and ATP synthesis

Identification of molecular and physiological changes in tomato in responses to aluminum stress and functional studies of aluminum responsive genes

Aluminum (Al) is one major toxic ion in acid soil (pH\u3c 5.0). This study aimed to determine the physiological and molecular changes induced by Al in tomato (Solanum lycopersicum \u27Micro-Tom\u27). Tomato plants were grown in hydroponic culture, and Al treatment was applied using 50&mgr;M aluminum sulfate [Al2 (SO4)3•18H 2O] or 50&mgr;M aluminum potassium sulfate dodecahydrate [KAl(SO 4)2•12H2O]. Mineral analysis found that Al 2(SO4)2 treated tomato contained a significant higher amount Al in roots (29-fold), and in green and orange and red tomato fruits (2-fold) (p\u3c 0.05). Morin (2\u27, 3, 4, 5, 7-pentahydroxyflavone) staining also detected a higher fluorescence intensity on Al treated roots. The treatment with aluminum potassium sulfate dodecahydrate resulted in shorter roots and a four-fold decrease in root size. In the relative and absolute quantitation (iTRAQ) proteomics analysis, 1442 proteins were identified in roots, of which 34 proteins showed significant changes in abundance between the Al-treated and control tissues (t- test with FDR corrections, p\u3c0.05, and \u3e 1.2-fold). Based on their putative cellular functions, the identified proteins are involved in metabolism of cell wall materials, plasma membrane changes, signal transduction, proteolysis, gene transcription, TCA cycle, glycolysis and detoxification . In green, orange and red tomato fruits, 124 of 1133 proteins, 39 of 1362 proteins, 44 of 1362 proteins, showed significant changes in abundance between the Al-treated and control tissues in each tissue type, respectively. Based on molecular functions, the identified proteins are involved in metabolism of cell wall materials, protein translation, energy regeneration, carbohydrate metabolism (glycolysis, TCA cycle, pentose phospate pathway, photosynthesis), intracellular trafficking protein, stress proteins (heat shock proteins, chaperonin, antioxidative enzymes, detoxification), post-translational modification and targeting and proteolysis, signal transduction and seed storage proteins. Proteins that are common to green, orange and red fruits (404 proteins), or those present only in one of the three maturity stages (395) were identified. Changes in those proteins corroborate with physiological processes, such as photosynthetic proteins were found only in green fruits. Transgenic tomato `Money Maker\u27 plants over expressing a lactoylglutathione lyase gene were generated. Three transgenic lines were confirmed to contain the insert gene. These transgenic lines are currently being evaluated for tolerance to Al toxicity