Molecular evolution of the plant ECERIFERUM1 and ECERIFERUM3 genes involved in aliphatic hydrocarbon production

Broad Chain-Length Specificity of the Alkane-Forming Enzymes NoCER1A and NoCER3A/B in Nymphaea odorata

Many terrestrial plants produce large quantities of alkanes for use in epicuticular wax and the pollen coat. However, their carbon chains must be long to be useful as fuel or as a petrochemical feedstock. Here, we focus on Nymphaea odorata, which produces relatively short alkanes in its anthers. We identified orthologs of the Arabidopsis alkane biosynthesis genes AtCER1 and AtCER3 in N. odorata and designated them NoCER1A, NoCER3A and NoCER3B. Expression analysis of NoCER1A and NoCER3A/B in Arabidopsis cer mutants revealed that the N. odorata enzymes cooperated with the Arabidopsis enzymes and that the NoCER1A produced shorter alkanes than AtCER1, regardless of which CER3 protein it interacted with. These results indicate that AtCER1 frequently uses a C30 substrate, whereas NoCER1A, NoCER3A/B and AtCER3 react with a broad range of substrate chain lengths. The incorporation of shorter alkanes disturbed the formation of wax crystals required for water-repellent activity in stems, suggesting that chain-length specificity is important for surface cleaning. Moreover, cultured tobacco cells expressing NoCER1A and NoCER3A/B effectively produced C19-C23 alkanes, indicating that the introduction of the two enzymes is sufficient to produce alkanes. Taken together, our findings suggest that these N. odorata enzymes may be useful for the biological production of alkanes of specific lengths. 3D modeling revealed that CER1s and CER3s share a similar structure that consists of N- and C-terminal domains, in which their predicted active sites are respectively located. We predicted the complex structure of both enzymes and found a cavity that connects their active sites.

Structural changes and adaptative evolutionary constraints in FLOWERING LOCUS T and TERMINAL FLOWER1-like genes of flowering plants

Regulation of flowering is a crucial event in the evolutionary history of angiosperms. The production of flowers is regulated through the integration of different environmental and endogenous stimuli, many of which involve the activation of different genes in a hierarchical and complex signaling network. The FLOWERING LOCUS T/TERMINAL FLOWER 1 (FT/TFL1) gene family is known to regulate important aspects of flowering in plants. To better understand the pivotal events that changed FT and TFL1 functions during the evolution of angiosperms, we reconstructed the ancestral sequences of FT/TFL1-like genes and predicted protein structures through in silico modeling to identify determinant sites that evolved in both proteins and allowed the adaptative diversification in the flowering phenology and developmental processes. In addition, we demonstrate that the occurrence of destabilizing mutations in residues located at the phosphatidylcholine binding sites of FT structure are under positive selection, and some residues of 4th exon are under negative selection, which is compensated by the occurrence of stabilizing mutations in key regions and the P-loop to maintain the overall protein stability. Our results shed light on the evolutionary history of key genes involved in the diversification of angiosperms.

Metalloenzymes for Fatty Acid-Derived Hydrocarbon Biosynthesis: Nature's Cryptic Catalysts

Waning resources, massive energy consumption, everdeepening global warming crisis, and climate change have raised grave concerns regarding continued dependence on fossil fuels as the predominant source of energy and generated tremendous interest for developing biofuels, which are renewable. Hydrocarbon-based 'drop-in' biofuels can be a proper substitute for fossil fuels such as gasoline or jet fuel. In Nature, hydrocarbons are produced by diverse organisms such as insects, plants, bacteria, and cyanobacteria. Metalloenzymes play a crucial role in hydrocarbons biosynthesis, and the past decade has witnessed discoveries of a number of metalloenzymes catalyzing hydrocarbon biosynthesis from fatty acids and their derivatives employing unprecedented mechanisms. These discoveries elucidated the enigma related to the divergent chemistries involved in the catalytic mechanisms of these metalloenzymes. There is substantial diversity in the structure, mode of action, cofactor requirement, and substrate scope among these metalloenzymes. Detailed structural analysis along with mutational studies of some of these enzymes have contributed significantly to identifying the key amino acid residues that dictate substrate specificity and catalytic intricacy. In this Review, we discuss the metalloenzymes that catalyze fatty acid-derived hydrocarbon biosynthesis in various organisms, emphasizing the active site architecture, catalytic mechanism, cofactor requirements, and substrate specificity of these enzymes. Understanding such details is essential for successfully implementing these enzymes in emergent biofuel research through protein engineering and synthetic biology approaches.

Origin and diversification of ECERIFERUM1 (CER1) and ECERIFERUM3 (CER3) genes in land plants and phylogenetic evidence that the ancestral CER1/3 gene resulted from the fusion of pre-existing domains

ECERIFERUM1 (CER1) and ECERIFERUM3 (CER3) are key genes in synthesis of alkanes, a major component of cuticular waxes in land plants. The genes share extensive similarity, including the N-terminal (ERG3/FAH) and C-terminal (WAX2) domains. This study, traces the origin, evolutionary history, phylogenetic relationships and variation in copy number of the two genes within and beyond the Viridiplantae (green plants). Protein homologs of both CER1 and CER3 were identified across most Embryophyta (land plants), a single homolog (CER1/3) in charophytes and prasinophytes, and none in the other green, red or brown algae. Ancestral state reconstructions in 100 sequenced Archaeplastida using presence/absence of CER1/3 family genes revealed that the CER1/3 gene probably originated in the common ancestor of Viridiplantae. Phylogenetic analysis of CER1 and CER3 protein sequences from 146 plant species strongly suggests that the two genes originated by duplication of CER1/3 in the ancestral embryophyte. The evolution of CER1 and CER3 genes involved differential divergence of the two domains. Outside Embryophyta, CER1/3 similar sequences identified in diatoms and a cryptophyte, were the closest relatives of the CER1/3 family proteins. Proteins harbouring WAX2-wxAR (WAX2 associated region) similar regions were identified in proteins of bacteria, Archaea, cryptophytes, dinoflagellates and Stramenopiles. The independent existence of both ERG3/FAH and WAX2-wxAR domains in diverse lineages strongly points to the origin of CER1/3 gene in green plants by the fusion of pre-existing domains.

Dissecting the Roles of Cuticular Wax in Plant Resistance to Shoot Dehydration and Low-Temperature Stress in Arabidopsis

Cuticular waxes are a mixture of hydrophobic very-long-chain fatty acids and their derivatives accumulated in the plant cuticle. Most studies define the role of cuticular wax largely based on reducing nonstomatal water loss. The present study investigated the role of cuticular wax in reducing both low-temperature and dehydration stress in plants using Arabidopsis thaliana mutants and transgenic genotypes altered in the formation of cuticular wax. cer3-6, a known Arabidopsis wax-deficient mutant (with distinct reduction in aldehydes, n-alkanes, secondary n-alcohols, and ketones compared to wild type (WT)), was most sensitive to water loss, while dewax, a known wax overproducer (greater alkanes and ketones compared to WT), was more resistant to dehydration compared to WT. Furthermore, cold-acclimated cer3-6 froze at warmer temperatures, while cold-acclimated dewax displayed freezing exotherms at colder temperatures compared to WT. Gas Chromatography-Mass Spectroscopy (GC-MS) analysis identified a characteristic decrease in the accumulation of certain waxes (e.g., alkanes, alcohols) in Arabidopsis cuticles under cold acclimation, which was additionally reduced in cer3-6. Conversely, the dewax mutant showed a greater ability to accumulate waxes under cold acclimation. Fourier Transform Infrared Spectroscopy (FTIR) also supported observations in cuticular wax deposition under cold acclimation. Our data indicate cuticular alkane waxes along with alcohols and fatty acids can facilitate avoidance of both ice formation and leaf water loss under dehydration stress and are promising genetic targets of interest.

ZmSRL5 is involved in drought tolerance by maintaining cuticular wax structure in maize

Cuticular wax is a natural barrier on terrestrial plant organs, which protects plants from damages caused by a variety of stresses. Here, we report the identification and functional characterization of a cuticular-wax-related gene, Zea mays L. SEMI-ROLLED LEAF 5 (ZmSRL5). The loss-of-function mutant srl5, which was created by a 3,745 bp insertion in the first intron that led to the premature transcript, exhibited abnormal wax crystal morphology and distribution, which, in turn, caused the pleiotropic phenotypes including increased chlorophyll leaching and water loss rate, decreased leaf temperature, sensitivity to drought, as well as semi-rolled mature leaves. However, total wax amounts showed no significant difference between wild type and semi-rolled leaf5 (srl5) mutant. The phenotype of srl5 was confirmed through the generation of two allelic mutants using CRISPR/Cas9. ZmSRL5 encodes a CASPARIAN-STRIP-MEMBRANE-DOMAIN-LIKE (CASPL) protein located in plasma membrane, and highly expressed in developing leaves. Further analysis showed that the expressions of the most wax related genes were not affected or slightly altered in srl5. This study, thus, primarily uncovers that ZmSRL5 is required for the structure formation of the cuticular wax and could increase the drought tolerance by maintaining the proper cuticular wax structure in maize.

Defensive Responses of Tea Plants (Camellia sinensis) Against Tea Green Leafhopper Attack: A Multi-Omics Study

Tea green leafhopper [Empoasca (Matsumurasca) onukii Matsuda] is one of the most devastating pests of tea plants (Camellia sinensis), greatly impacting tea yield and quality. A thorough understanding of the interactions between the tea green leafhopper and the tea plant would facilitate a better pest management. To gain more insights into the molecular and biochemical mechanisms behind their interactions, a combined analysis of the global transcriptome and metabolome reconfiguration of the tea plant challenged with tea green leafhoppers was performed for the first time, complemented with phytohormone analysis. Non-targeted metabolomics analysis by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF MS), together with quantifications by ultra-performance liquid chromatography triple quadrupole mass spectrometry (UPLC-QqQ MS), revealed a marked accumulation of various flavonoid compounds and glycosidically bound volatiles but a great reduction in the level of amino acids and glutathione upon leaf herbivory. RNA-Seq data analysis showed a clear modulation of processes related to plant defense. Genes pertaining to the biosynthesis of phenylpropanoids and flavonoids, plant-pathogen interactions, and the biosynthesis of cuticle wax were significantly up-regulated. In particular, the transcript level for a CER1 homolog involved in cuticular wax alkane formation was most drastically elevated and an increase in C29 alkane levels in tea leaf waxes was observed. The tea green leafhopper attack triggered a significant increase in salicylic acid (SA) and a minor increase in jasmonic acid (JA) in infested tea leaves. Moreover, transcription factors (TFs) constitute a large portion of differentially expressed genes, with several TFs families likely involved in SA and JA signaling being significantly induced by tea green leafhopper feeding. This study presents a valuable resource for uncovering insect-induced genes and metabolites, which can potentially be used to enhance insect resistance in tea plants.