Reassessing the evolution of the 1-deoxy-D-xylulose 5-phosphate synthase family suggests a possible novel function for the DXS class 3 proteins.

The methylerythritol 4-phosphate (MEP) pathway is of paramount importance for generating plastidial isoprenoids. The first enzyme of the MEP pathway, 1-deoxy-D-xylulose-5-phosphate synthase (DXS), catalyzes a flux-controlling step. In plants the DXS gene family is composed of three distinct classes with non-redundant functions. Although the DXS1 and DXS2 subfamilies have been well characterized, the DXS3 subfamily has been considerably understudied. Here, we carried out in silico and functional analyses to better understand the DXS3 class. Our phylogenetic analysis showed high variation in copy number among the different DXS classes, with the apparent absence of DXS1 class in some species. We found that DXS3 subfamily emerged later than DXS1 and DXS2 and it is under less intense purifying selection. Furthermore, in the DXS3 subfamily critical amino acids positions in the thiamine pyrophosphate binding pocket are not conserved. We demonstrated that the DXS3 proteins from Arabidopsis, Maize, and Rice lack functional DXS activity. Moreover, the Arabidopsis DXS3 protein displayed distinctive sub-organellar chloroplast localization not observed in any DXS1 or DXS2 proteins. Co-expression analysis of the DXS3 from Arabidopsis showed that, unlike DXS1 and DXS2 proteins, it co-expresses with genes related to post-embryonic development and reproduction and not with primary metabolism and isoprenoid synthesis.

Visualization of Carotenoid-Storage Structures in Fruits by Transmission Electron Microscopy.

Plastids are cell organelles that, beside other functions, have the capability to store carotenoids in specialized structures, which may vary among the different plant species, tissues or according to the carotenoid complement. Fruits are an important source of carotenoids, and during ripening, chloroplasts differentiate into chromoplasts that are able to accumulate large amounts of carotenoids, rendering then the characteristic fruit coloration. Whereas lycopene or ß-carotene may accumulate as crystal in the chromoplasts of some fruit, other xanthophyll-accumulating fruits differentiate plastoglobuli as a preferred system to enhance carotenoids stability and storage. Visualization of plastid ultrastructure and their transformation during ripening or in fruit of contrasting coloration are fundamental objectives within carotenoids research in fruits. Therefore, in this chapter, we describe a protocol for the visualization and analysis of plastid ultrastructure by transmission electron microscopy (TEM), specially designed and adapted to fruit tissues.

Deep proteome analysis of gerontoplasts from the inner integument of developing seeds of Jatropha curcas.

UNLABELLED: The inner integument of Jatropha curcas seeds is a non-photosynthetic tissue that acts primarily as a conduit for the delivery of nutrients to the embryo and endosperm. In this study we performed a histological and transmission electron microscopy analysis of the inner integument in stages prior to fertilization to 25days after pollination, to establish the structural changes associated with the plastid to gerontoplast transition. This study showed that plastids are subjected to progressive changes, which include the dismantling of the internal membrane system, matrix degradation and the formation of stromule-derived vesicles. A proteome analysis of gerontoplasts isolated from the inner integument at 25days after pollination, resulted in the identification of 1923 proteins, which were involved in a myriad of metabolic functions, such as synthesis of amino acids and fatty acids. Among the identified proteins, were also a number of hydrolases (peptidases, lipases and carbohydrases), which presumably are involved in the ordered dismantling of this organelle to provide additional sources of nutrients for the growing embryo and endosperm. The dataset we provide here may provide a foundation for the study of the proteome changes associated with the plastid to gerontoplast transition in non-photosynthetic tissues. SIGNIFICANCE: We describe ultrastructural features of gerontoplasts isolated from the inner integument of developing seeds of Jatropha curcas, together with a deep proteome analysis of these gerontoplasts. This article explores a new aspect of the biology of plastids, namely the ultrastructural and proteome changes associated with the transition plastid to gerontoplast in a non-photosynthetic tissue.

Ultrastructural changes in the epidermis of petals of the sweet orange infected by Colletotrichum acutatum.

Postbloom fruit drop (PFD) is an important disease caused by the fungus Colletotrichum acutatum. PFD is characterised by the formation of necrotic lesions on the petals and stigmas of flowers as well as premature abscission of the fruit in Citrus spp. We compare the ultrastructure of the epidermis of uninoculated Citrus sinensis petals with that of petals inoculated with the fungus to understand the changes that occur upon C. acutatum infection. Healthy petals have a cuticle with parallel striations covering the uniseriate epidermis. This pattern consists of vacuolated parietal cells whose cytoplasm contains mitochondria, plastids with an undeveloped endomembrane system and a slightly dense stroma, a poorly developed rough endoplasmic reticulum, polysomes, few lipid droplets, and a nucleus positioned near the inner periclinal wall. In damaged regions, the cytoplasm of some cells is densely packed with well-developed endoplasmic reticulum, a large number of hyperactive dictyosomes, numerous mitochondria, and many lipid droplets. The plastids have an electron-dense stroma, starch grains, and a large amount of electron-dense lipid droplets, which can be released into vacuoles or the endoplasmic reticulum. Multivesicular bodies and myelin bodies are frequently observed in the vacuole, cytoplasm, and periplasmic space. Vesicles migrate through the cell wall and are involved in the deposition of cuticular material. In the later stages of infection, there is deposition of new cuticle layers in plaques. The outer periclinal walls can be thick. These observations indicate that epidermal cells respond to the pathogen, resulting in cuticular and parietal changes, which may limit further infection.

Estudio del desarrollo, calidad de planta y acumulación de pigmentos en lígulas de tagetes erecta l: expuestas a dos intensidades de luz / Study of development, quality of plant and accumulation of pigments in ligules of tagetes erecta l: exposed to two light intensities

The carotenoids are photosensitive pigments during photosynthesis. The objective of this work was to study the effect on development and accumulation of carotenoids in ligules of Tagetes erecta exposed under two different lighting ambient (with mesh and without mesh of 50 percent). The plant development was evaluated measuring the height of the plant, number of floral buds, the ligules diameter. In adition, the quantification and identification of carotenoids from ligules was done by HPLC. The results showed significant differences (p<0.05) in the height of the plant, number of floral buds and ligules diameter of T. erecta. The group grown without mesh received greater UV radiation and different temperature, that under a mesh. The first conditions lead to a reduction of the ligules diameter and total content of xanthophylls (lutein and zeaxanthin). The plastids ultrastructure in the cells of T. erecta developed with mesh showed the greatest amount of thylakoid membranes and more conspicuous starch granules.

Los carotenoides son pigmentos fotosensibles frente a un exceso de intensidad luminosa durante el proceso de fotosíntesis. El objetivo de este trabajo fue el estudio del efecto en el desarrollo de la planta y la acumulación de carotenoides por la exposición a dos diferentes intensidades lumínicas (con y sin malla de sombra al 50 por ciento). Se evaluó el desarrollo de T. erecta en cuanto a la altura de la planta, número de botones florales y el diámetro de las lígulas. Adicionalmente, en las lígulas se cuantificaron e identificaron los carotenoides por HPLC. Los resultados mostraron diferencias significativas (p<0.05) en cuanto al desarrollo de las plantas expuestas a mayor radiación UV y temperatura, presentaron reducción del diámetro de las lígulas y disminución en el contenido de Xantófilas totales ( luteína y zeaxantina) con respecto a las cultivadas con malla,. La ultraestructura de los plastidios mostró mayor cantidad de membranas tilacoidales y gránulos de almidón más conspicuos en las células de las plantas de T erecta desarrolladas con malla.