Identification and differential accumulation of two isoforms of the CF1-beta subunit under high light stress in Brassica rapa

Quantitative Proteomics Reveals Common and Specific Responses of a Marine Diatom Thalassiosira pseudonana to Different Macronutrient Deficiencies

Macronutrients such as nitrogen (N), phosphorus (P), and silicon (Si) are essential for the productivity and distribution of diatoms in the ocean. Responses of diatoms to a particular macronutrient deficiency have been investigated, however, we know little about their common or specific responses to different macronutrients. Here, we investigated the physiology and quantitative proteomics of a diatom Thalassiosira pseudonana grown in nutrient-replete, N-, P-, and Si-deficient conditions. Cell growth was ceased in all macronutrient deficient conditions while cell volume and cellular C content under P- and Si-deficiencies increased. Contents of chlorophyll a, protein and cellular N decreased in both N- and P-deficient cells but chlorophyll a and cellular N increased in the Si-deficient cells. Cellular P content increased under N- and Si-deficiencies. Proteins involved in carbon fixation and photorespiration were down-regulated under all macronutrient deficiencies while neutral lipid synthesis and carbohydrate accumulation were enhanced. Photosynthesis, chlorophyll biosynthesis, and protein biosynthesis were down-regulated in both N- and P-deficient cells, while Si transporters, light-harvesting complex proteins, chloroplastic ATP synthase, plastid transcription and protein synthesis were up-regulated in the Si-deficient cells. Our results provided insights into the common and specific responses of T. pseudonana to different macronutrient deficiencies and identified specific proteins potentially indicating a particular macronutrient deficiency.

One dry summer: a leaf proteome study on the response of oak to drought exposure

One of the most prominent hallmarks of the expected climate change in Europe is the higher prevalence of longer and more intense periods of summer drought. To preserve European oak forests, of considerable importance for European economical and ecological development, under these conditions knowledge on the mechanisms by which broad-leaved trees cope with drought is needed. In this study the effect of one season of drought stress, corresponding in length and soil water content to a dry summer, on young pedunculate oak trees (Quercus robur L.) was investigated by monitoring phenotypical parameters, the analysis of carbohydrate accumulation and a 2D-DIGE-based proteome study of leaves. In our experimental system, mimicking the conditions of a dry summer, the plants displayed reduced growth, moreover the transition through the developmental stages was affected. The data obtained during this study, supported by a separately published gene expression analysis study, indicated that the oak tried to adapt its metabolism in order to maintain its full molecular functionality. Initially the plants seemed to be able to cope with the imposed stress. However prolonged drought exposure overwhelmed the adaptive mechanisms and at the last sampling point of this study the molecular machinery succumbed.

Growth inhibition in Chinese cabbage (Brassica rapa var. chinensis) growth exposed to di-n-butyl phthalate

The toxicity and effects of di-n-butyl phthalate (DBP), an endocrine disruptor, on the growth of Chinese cabbage (Brassica rapa var. chinensis) were studied. Etiolation occurred on leaves of Chinese cabbage plant treated with 50mg/L of DBP for 42 d. DBP even below 1mg/L had a significant effect on the concentration of chlorophyll in Chinese cabbage and the biomass showed a severe decrease under treatment with more than 30 mg/L of DBP. At a concentration below 1mg/L of DBP, no significant difference in accumulation was found, but treatments with concentration exceeding 10, 30, 50 and 100mg/L all resulted in significant accumulation of DBP. Six protein spots extracted from leaf tissue of DBP-treated Chinese cabbage displaying a differential expression are shown in 2-DE maps. According to proteome level studies, three protein spots were found to increase and were identified, respectively, as acyl-[acyl-carrier-protein] desaturase (acyl-ACP desaturase), root phototropism protein 3 (RPT3) and ferredoxin-nitrite reductase (Fd-NiR). The other three protein spots were found to decrease and were identified respectively as dihydroflavonol-4-reductase (DFR), aminoacyl-tRNA synthetase (aaRS) and ATP synthase subunit beta. The key finding is that the other closely related plant, Bok choy (Brassica rapa subsp. chinensis), the subspecies of Chinese cabbage, respond differently to the same chemicals.

The long-term responses of the photosynthetic proton circuit to drought

Proton motive force (pmf) across thylakoid membranes is not only for harnessing solar energy for photosynthetic CO(2) fixation, but also for triggering feedback regulation of photosystem II antenna. The mechanisms for balancing these two roles of the proton circuit under the long-term environmental stress, such as prolonged drought, have been poorly understood. In this study, we report on the response of wild watermelon thylakoid 'proton circuit' to drought stress using both in vivo spectroscopy and molecular analyses of the representative photosynthetic components. Although drought stress led to enhanced proton flux via a approximately 34% increase in cyclic electron flow around photosystem I (PS I), an observed approximately fivefold decrease in proton conductivity, g(H)(+), across thylakoid membranes suggested that decreased ATP synthase activity was the major factor for sustaining elevated q(E). Western blotting analyses revealed that ATP synthase content decreased significantly, suggesting that quantitative control of the complex plays a pivotal role in down-regulation of g(H)(+). The expression level of cytochrome b(6)f complex - another key control point in photosynthesis - also declined, probably to prevent excess-reduction of PS I electron acceptors. We conclude that plant acclimation to long-term environmental stress involves global changes in the photosynthetic proton circuit, in which ATP synthase represents the key control point for regulating the relationship between electron transfer and pmf.

Proteome analysis and characterization of phenotypes of lesion mimic mutant spotted leaf 6 in rice

Rice spotted leaf 6 (spl6) mutant produces lesions caused by spontaneous cell death in the absence of pathogenic infection. Expression of this genetic trait was developmentally programmed. After the tillering stage, small red and brown lesions were initiated in groups on the leaf blade. Eventually, the lesions formed parallel lines along the midrib of the leaf. Under light and transmission electron microscopy, we observed that thylakoid membranes of mesophyll chloroplasts were progressively damaged in the nonspotted section of the mutant leaf. However, chloroplasts were absent in the mesophyll cells of the spotted area of the spl6 mutant. These results indicated that lesion formation of the spl6 mutant might be caused by oxidative burst. Proteome analysis revealed that 159 protein spots were up or downregulated in comparison between spotted leaves of the spl6 mutant plants and normal leaves of the wild type. Among them, protein disulfide isomerase (PDI), transketolase, thioredoxin peroxidase (TPX), ATP synthase, RuBisCO large subunit, and RuBisCO activase small subunit were not identified in the spl6 mutant but were abundant in the wild type. Especially, the absence of TPX and PDI might be the cause of the failure to protect cells against oxidative burst resulting in degradation of the thylakoid membranes and leading to programmed cell death and lesion development.

An Arabidopsis thaliana virescent mutant reveals a role for ClpR1 in plastid development

The ATP-dependent Clp protease has been well-characterized in Escherichia coli, but knowledge of its function in higher plants is limited. In bacteria, this two-component protease consists of a Ser-type endopeptidase ClpP, which relies on the ATP-dependent unfolding activity from an Hsp100 molecular chaperone to initiate protein degradation. In the chloroplasts of higher plants, multiple isoforms of the proteolytic subunit exist, with Arabidopsis having five ClpPs and four ClpP-like proteins termed ClpR predicted in its genome. In this work we characterized an Arabidopsis mutant impaired in one subunit of the chloroplast-localized Clp protease core, ClpR1. clpR1-1, a virescent mutant, carries a pre-mature stop codon in the clpR1 gene, resulting in no detectable ClpR1 protein. The accumulation of several chloroplast proteins, as well as most of the chloroplast-localized Clp protease subunits, is inhibited in clpR1-1. Unexpectedly, some plastid-encoded proteins do not accumulate, although their transcripts accumulate to wild-type levels. Maturation of 23S and 4.5S chloroplast ribosomal RNA (cp-rRNA) is delayed in clpR1-1, and both RNAs accumulate as higher molecular weight precursors. Also, chloroplasts in clpR1-1 are smaller than in wild type and have fewer thylakoid membranes with smaller grana stacks. We propose that a ClpR1-containing activity is required for chloroplast development and differentiation and in its absence both are delayed.