Reductive evolution of chloroplasts in non-photosynthetic plants, algae and protists.

Chloroplasts are generally known as eukaryotic organelles whose main function is photosynthesis. They perform other functions, however, such as synthesizing isoprenoids, fatty acids, heme, iron sulphur clusters and other essential compounds. In non-photosynthetic lineages that possess plastids, the chloroplast genomes have been reduced and most (or all) photosynthetic genes have been lost. Consequently, non-photosynthetic plastids have also been reduced structurally. Some of these non-photosynthetic or "cryptic" plastids were overlooked or unrecognized for decades. The number of complete plastid genome sequences and/or transcriptomes from non-photosynthetic taxa possessing plastids is rapidly increasing, thus allowing prediction of the functions of non-photosynthetic plastids in various eukaryotic lineages. In some non-photosynthetic eukaryotes with photosynthetic ancestors, no traces of plastid genomes or of plastids have been found, suggesting that they have lost the genomes or plastids completely. This review summarizes current knowledge of non-photosynthetic plastids, their genomes, structures and potential functions in free-living and parasitic plants, algae and protists. We introduce a model for the order of plastid gene losses which combines models proposed earlier for land plants with the patterns of gene retention and loss observed in protists. The rare cases of plastid genome loss and complete plastid loss are also discussed.

Building a biofactory: Constructing glandular trichomes in Cannabis sativa.

Flowers of Cannabis sativa L. are densely covered with glandular trichomes containing cannabis resin that is used for medicinal and recreational purposes. The highly productive glandular trichomes have been described as 'biofactories.' In this review, we use this analogy to highlight recent advances in cannabis cell biology, metabolomics, and transcriptomics. The biofactory is built by epidermal outgrowths that differentiate into peltate-like glandular trichome heads, consisting of a disc of interconnected secretory cells with unique cellular structures. Cannabinoid and terpenoid products are warehoused in the extracellular storage cavity. Finally, multicellular stalks raise the glandular heads above the epidermis, giving cannabis flower their frosty appearance.

Apicomplexan-like parasites are polyphyletic and widely but selectively dependent on cryptic plastid organelles.

The phylum Apicomplexa comprises human pathogens such as Plasmodium but is also an under-explored hotspot of evolutionary diversity central to understanding the origins of parasitism and non-photosynthetic plastids. We generated single-cell transcriptomes for all major apicomplexan groups lacking large-scale sequence data. Phylogenetic analysis reveals that apicomplexan-like parasites are polyphyletic and their similar morphologies emerged convergently at least three times. Gregarines and eugregarines are monophyletic, against most expectations, and rhytidocystids and Eleutheroschizon are sister lineages to medically important taxa. Although previously unrecognized, plastids in deep-branching apicomplexans are common, and they contain some of the most divergent and AT-rich genomes ever found. In eugregarines, however, plastids are either abnormally reduced or absent, thus increasing known plastid losses in eukaryotes from two to four. Environmental sequences of ten novel plastid lineages and structural innovations in plastid proteins confirm that plastids in apicomplexans and their relatives are widespread and share a common, photosynthetic origin.

Expression analysis of the Arabidopsis CP12 gene family suggests novel roles for these proteins in roots and floral tissues.

The chloroplast protein CP12 has been shown to regulate the activity of two Calvin cycle enzymes, phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), by the reversible formation of a multiprotein complex. In Arabidopsis there are three CP12 genes, CP12-1, CP12-2, and CP12-3, and expression analysis suggested that the function of these proteins may not be restricted to the Calvin cycle. Reverse transcription-PCR analysis was used here to investigate further the expression patterns of the three CP12 Arabidopsis genes together with the genes encoding plastid GAPDH (GAPA-1 and GAPB), PRK (PRK), and plastid NAD-dependent GAPDH (GAPCp1 and GAPCp2) during development, in response to changes in light, temperature, and anaerobic conditions. Expression of the CP12-2 gene was similar to that of the Calvin cycle enzymes PRK and GAPDH. However, this was not the case for CP12-1 and -3 which were both expressed in roots. Analysis of transgenic Arabidopsis lines expressing CP12::GUS fusion constructs revealed that the CP12 genes display different spatiotemporal expression patterns. The CP12-1 gene was expressed in root tips whilst CP12-3::GUS expression was evident throughout the root tissue. The most unexpected finding was that all three CP12 genes were expressed in floral tissues; CP12-1 and CP12-2 expression was detected in the sepals and the style of the flower, while in contrast CP12-3::GUS expression was restricted to the stigma and anthers. Taken together, the data suggest that the redox-sensitive CP12 proteins may have a wider role in non-photosynthetic plastids, throughout the plant life cycle.

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.