Caleosin/peroxygenases: multifunctional proteins in plants

Domestication has altered gene expression and secondary metabolites in pea seed coat

The mature seed in legumes consists of an embryo and seed coat. In contrast to knowledge about the embryo, we know relatively little about the seed coat. We analyzed the gene expression during seed development using a panel of cultivated and wild pea genotypes. Gene co-expression analysis identified gene modules related to seed development, dormancy, and domestication. Oxidoreductase genes were found to be important components of developmental and domestication processes. Proteomic and metabolomic analysis revealed that domestication favored proteins involved in photosynthesis and protein metabolism at the expense of seed defense. Seed coats of wild peas were rich in cell wall-bound metabolites and the protective compounds predominated in their seed coats. Altogether, we have shown that domestication altered pea seed development and modified (mostly reduced) the transcripts along with the protein and metabolite composition of the seed coat, especially the content of the compounds involved in defense. We investigated dynamic profiles of selected identified phenolic and flavonoid metabolites across seed development. These compounds usually deteriorated the palatability and processing of the seeds. Our findings further provide resources to study secondary metabolism and strategies for improving the quality of legume seeds which comprise an important part of the human protein diet.

Unveiling the applications of membrane proteins from oil bodies: leading the way in artificial oil body technology and other biotechnological advancements

Oil bodies (OBs) function as organelles that store lipids in plant seeds. An oil body (OB) is encased by a membrane composed of proteins (e.g., oleosins, caleosins, and steroleosins) and a phospholipid monolayer. The distinctive protein-phospholipid membrane architecture of OBs imparts exceptional stability even in extreme environments, thereby sparking increasing interest in their structure and properties. However, a comprehensive understanding of the structure-activity relationships determining the stability and properties of oil bodies requires a more profound exploration of the associated membrane proteins, an aspect that remains relatively unexplored. In this review, we aim to summarize and discuss the structural attributes, biological functions, and properties of OB membrane proteins. From a commercial perspective, an in-depth understanding of the structural and functional properties of OBs is important for the expansion of their applications by producing artificial oil bodies (AOB). Besides exploring their structural intricacies, we describe various methods that are used for purifying and isolating OB membrane proteins. These insights may provide a foundational framework for the practical utilization of OB membrane proteins in diverse applications within the realm of AOB technology, including biological and probiotic delivery, protein purification, enzyme immobilization, astringency detection, and antibody production.

Proteome plasticity during Physcomitrium patens spore germination - from the desiccated phase to heterotrophic growth and reconstitution of photoautotrophy

The establishment of moss spores is considered a milestone in plant evolution. They harbor protein networks underpinning desiccation tolerance and accumulation of storage compounds that can be found already in algae and that are also utilized in seeds and pollen. Furthermore, germinating spores must produce proteins that drive the transition through heterotrophic growth to the autotrophic plant. To get insight into the plasticity of this proteome, we investigated it at five timepoints of moss (Physcomitrium patens) spore germination and in protonemata and gametophores. The comparison to previously published Arabidopsis proteome data of seedling establishment showed that not only the proteomes of spores and seeds are functionally related, but also the proteomes of germinating spores and young seedlings. We observed similarities with regard to desiccation tolerance, lipid droplet proteome composition, control of dormancy, and β-oxidation and the glyoxylate cycle. However, there were also striking differences. For example, spores lacked any obvious storage proteins. Furthermore, we did not detect homologs to the main triacylglycerol lipase in Arabidopsis seeds, SUGAR DEPENDENT1. Instead, we discovered a triacylglycerol lipase of the oil body lipase family and a lipoxygenase as being the overall most abundant proteins in spores. This finding indicates an alternative pathway for triacylglycerol degradation via oxylipin intermediates in the moss. The comparison of spores to Nicotiana tabacum pollen indicated similarities for example in regards to resistance to desiccation and hypoxia, but the overall developmental pattern did not align as in the case of seedling establishment and spore germination.

Polyamine depletion enhances oil body mobilization through possible regulation of oleosin degradation and aquaporin abundance on its membrane

Oil body (OB) mobilization, a crucial event associated with early seedling growth, is delayed in response to salt stress. Previous reports suggest that careful regulation of polyamine (PA) metabolism is essential for salt stress tolerance in plants. Many aspects of PA-mediated regulation of metabolism have been uncovered. However, their role in the process of OB mobilization remains unexplored. Interestingly, the present investigations reveal a possible influence of PA homeostasis on OB mobilization, while implicating complex regulation of oleosin degradation and aquaporin abundance in OB membranes in the process. Application of PA inhibitors resulted in the accumulation of smaller OBs when compared to control (-NaCl) and the salt-stressed counterparts, suggesting a faster rate of mobilization. PA deficit also resulted in reduced retention of some larger oleosins under controlled conditions but enhanced retention of all oleosins under salt stress. Additionally, with respect to aquaporins, a higher abundance of PIP2 under PA deficit both under control and saline conditions, is correlated with a faster mobilization of OBs. Contrarily, TIP1s, and TIP2s remained almost undetectable in response to PA depletion and were differentially regulated by salt stress. The present work, thus, provides novel insights into PA homeostasis-mediated regulation of OB mobilization, oleosin degradation, and aquaporin abundance on OB membranes.

Molecular Machinery of Lipid Droplet Degradation and Turnover in Plants

Lipid droplets (LDs) are important organelles conserved across eukaryotes with a fascinating biogenesis and consumption cycle. Recent intensive research has focused on uncovering the cellular biology of LDs, with emphasis on their degradation. Briefly, two major pathways for LD degradation have been recognized: (1) lipolysis, in which lipid degradation is catalyzed by lipases on the LD surface, and (2) lipophagy, in which LDs are degraded by autophagy. Both of these pathways require the collective actions of several lipolytic and proteolytic enzymes, some of which have been purified and analyzed for their in vitro activities. Furthermore, several genes encoding these proteins have been cloned and characterized. In seed plants, seed germination is initiated by the hydrolysis of stored lipids in LDs to provide energy and carbon equivalents for the germinating seedling. However, little is known about the mechanism regulating the LD mobilization. In this review, we focus on recent progress toward understanding how lipids are degraded and the specific pathways that coordinate LD mobilization in plants, aiming to provide an accurate and detailed outline of the process. This will set the stage for future studies of LD dynamics and help to utilize LDs to their full potential.

Lipid droplets are versatile organelles involved in plant development and plant response to environmental changes

Since decades plant lipid droplets (LDs) are described as storage organelles accumulated in seeds to provide energy for seedling growth after germination. Indeed, LDs are the site of accumulation for neutral lipids, predominantly triacylglycerols (TAGs), one of the most energy-dense molecules, and sterol esters. Such organelles are present in the whole plant kingdom, from microalgae to perennial trees, and can probably be found in all plant tissues. Several studies over the past decade have revealed that LDs are not merely simple energy storage compartments, but also dynamic structures involved in diverse cellular processes like membrane remodeling, regulation of energy homeostasis and stress responses. In this review, we aim to highlight the functions of LDs in plant development and response to environmental changes. In particular, we tackle the fate and roles of LDs during the plant post-stress recovery phase.