SPL13 together with SPL9 redundantly regulates wax biosynthesis upon drought stress.

Wax biosynthesis is strictly regulated by many regulators under different environmental conditions. Our previous study showed that the regulation module miR156/SQUAMOSA PROMOTER BINDING PROTEIN-LIKE9 (SPL9)/DEWAX is identified to be involved in the diurnal regulation of wax production, however, it was unknown if other SPLs are also involved in the wax synthesis. Here, we reported that SPL13 regulates drought-induced wax production as well. Moreover, its regulatory role directly or indirectly affects the expression of two wax biosynthesis genes CER1 and CER4. Further study showed that SPL13 together with SPL9 redundantly regulated the wax accumulation upon either normal conditions or drought stress, simultaneous mutation of both genes additively enhanced cuticle permeability and decreased the drought tolerance. However, different from SPL9, SPL13 seemed not to participate in the DEWAX-mediated diurnal regulation of wax production.

Acetyl-CoA Carboxylase1 Influences ECERIFERUM2 Activity to Mediate the Synthesis of Very-Long-Chain Fatty Acid Past C28.

Cuticular wax is a protective layer on the aerial surfaces of land plants. In Arabidopsis (Arabidopsis thaliana), cuticular wax is mainly constituted of compounds derived from very-long-chain fatty acids (VLCFAs) with chain lengths longer than C28. CER2-LIKE (ECERIFERUM2-LIKE) proteins interact with CER6/KCS6 (ECERIFERUM6/ß-Ketoacyl-CoA Synthase6), the key enzyme of the fatty acid elongase complex, to modify its substrate specificity for VLCFA elongation past C28. However, the molecular regulatory mechanism of CER2-LIKE proteins remains unclear. Arabidopsis eceriferum19 (cer19) mutants display wax-deficient stems caused by loss of waxes longer than C28, indicating that CER19 may participate in the CER2-LIKE-mediated VLCFA elongation past C28. Using positional cloning and genetic complementation, we showed that CER19 encodes Acetyl-CoA Carboxylase1 (ACC1), which catalyzes the synthesis of malonyl-CoA, the essential substrate for the CER6/KCS6-mediated condensation reaction in VLCFA synthesis. We demonstrated that ACC1 physically interacts with CER2-LIKE proteins via split-ubiquitin yeast two-hybrid (SUY2H) and firefly luciferase complementation imaging (LCI) analysis. Additionally, heterologous expression in yeast and genetic analysis in Arabidopsis revealed that ACC1 affects CER2 activity to influence VLCFA elongation past C28. These findings imply that CER2-LIKE proteins might function as a link between ACC1 and CER6/KCS6 and subsequently enhance CER6/KCS6 binding to malonyl-CoA for further utilization in VLCFA elongation past C28. This information deepens our understanding of the complex mechanism of cuticular wax biosynthesis.

The Arabidopsis cytochrome P450 enzyme CYP96A4 is involved in the wound-induced biosynthesis of cuticular wax and cutin monomers.

The plant cuticle is composed of cuticular wax and cutin polymers and plays an essential role in plant tolerance to diverse abiotic and biotic stresses. Several stresses, including water deficit and salinity, regulate the synthesis of cuticular wax and cutin monomers. However, the effect of wounding on wax and cutin monomer production and the associated molecular mechanisms remain unclear. In this study, we determined that the accumulation of wax and cutin monomers in Arabidopsis leaves is positively regulated by wounding primarily through the jasmonic acid (JA) signaling pathway. Moreover, we observed that a wound- and JA-responsive gene (CYP96A4) encoding an ER-localized cytochrome P450 enzyme was highly expressed in leaves. Further analyses indicated that wound-induced wax and cutin monomer production was severely inhibited in the cyp96a4 mutant. Furthermore, CYP96A4 interacted with CER1 and CER3, the core enzymes in the alkane-forming pathway associated with wax biosynthesis, and modulated CER3 activity to influence aldehyde production in wax synthesis. In addition, transcripts of MYC2 and JAZ1, key genes in JA signaling pathway, were significantly reduced in cyp96a4 mutant. Collectively, these findings demonstrate that CYP96A4 functions as a cofactor of the alkane synthesis complex or participates in JA signaling pathway that contributes to cuticular wax biosynthesis and cutin monomer formation in response to wounding.

Function identification of Arabidopsis GPAT4 and GPAT8 in the biosynthesis of suberin and cuticular wax.

Surface lipids in plants include cutin, cuticular wax and suberin. sn-Glycerol-3-phosphate acyltransferases (GPATs) facilitate the acylation of sn-glycerol-3-phosphate (G3P) utilizing a fatty acyl group from acyl-coenzyme A (acyl-CoA) or acyl-acyl carrier protein (acyl-ACP) as substrates for the biosynthesis of plant extracellular lipids such as suberin and cutin. Here we found that Arabidopsis GPAT4 and GPAT8 are specifically expressed in endodermis cells of roots where suberin was accumulated. GPAT4 mutation significantly decreased the amounts of the C16 and C18 ω-oxidized suberin monomers, whereas the mutation of GPAT8 had little effect on the suberin production, and the functions of both were not redundant. Root suberin phenotype analysis of gpat4-1 and gpat6-1 single or double mutant revealed that GPAT4 and GPAT6 play redundant functions. Interestingly, the gpat4-1 gpat8-1 double mutant displayed a glossy stem phenotype since fewer wax crystals were accumulated. This phenotype was not shown in either parent. Further study showed that the amounts of most wax components were significantly decreased. Taken together, our findings revealed that GPAT4 has an additive effect with GPAT6 in the root suberin biosynthesis, and plays a redundant role in wax production with GPAT8.

Exploring domestication pattern in lotus: insights from dispensable genome assembly.

Lotus (Nelumbo nucifera Gaertn.), an important aquatic plant in horticulture and ecosystems, has been cultivated for more than 7000 years and domesticated into three different subgroups: flower lotus, rhizome lotus, and seed lotus. To explore the domesticated regions of each subgroup, re-sequencing data of 371 lotus accessions collected from the public database were aligned to the genome of 'China-Antique (CA)'. Unmapped reads were used to build the dispensable genome of each subgroup using a metagenome-like assembly strategy. More than 27 Mb of the dispensable genome in these three subgroups and the wild group was assembled, of which 11,761 genes were annotated. Some of the contigs in the dispensable genome were similar to the genomic segments of other lotus accessions other than 'CA'. The annotated genes in each subgroup played essential roles in specific developmental processes. Dissection of selective signals in three cultivated subgroups also demonstrated that subgroup-specific metabolic pathways, such as the brassinosteroids metabolism enrichment in FL, associated with these selected genes in each subgroup and the contigs in dispensable genome nearly located in the domesticated regions of each subgroup, respectively. Our data presented a valuable resource for facilitating lotus genomic studies, complemented the helpful information to the reference genome, and shed light on the selective signals of domesticated subgroups.

The evolutionary innovation of root suberin lamellae contributed to the rise of seed plants.

Seed plants overtook ferns to become the dominant plant group during the late Carboniferous, a period in which the climate became colder and dryer1,2. However, the specific innovations driving the success of seed plants are not clear. Here we report that the appearance of suberin lamellae (SL) contributed to the rise of seed plants. We show that the Casparian strip and SL vascular barriers evolved at different times, with the former originating in the most recent common ancestor (MRCA) of vascular plants and the latter in the MRCA of seed plants. Our results further suggest that most of the genes required for suberin formation arose through gene duplication in the MRCA of seed plants. We show that the appearance of the SL in the MRCA of seed plants enhanced drought tolerance through preventing water loss from the stele. We hypothesize that SL provide a decisive selective advantage over ferns in arid environments, resulting in the decline of ferns and the rise of gymnosperms. This study provides insights into the evolutionary success of seed plants and has implications for engineering drought-tolerant crops or fern varieties.

Regulatory network of rice in response to heat stress and its potential application in breeding strategy.

The rapid development of global industrialization has led to serious environmental problems, among which global warming has become one of the major concerns. The gradual rise in global temperature resulted in the loss of food production, and hence a serious threat to world food security. Rice is the main crop for approximately half of the world's population, and its geographic distribution, yield, and quality are frequently reduced due to elevated temperature stress, and breeding rice varieties with tolerance to heat stress is of immense significance. Therefore, it is critical to study the molecular mechanism of rice in response to heat stress. In the last decades, large amounts of studies have been conducted focusing on rice heat stress response. Valuable information has been obtained, which not only sheds light on the regulatory network underlying this physiological process but also provides some candidate genes for improved heat tolerance breeding in rice. In this review, we summarized the studies in this field. Hopefully, it will provide some new insights into the mechanisms of rice under high temperature stress and clues for future engineering breeding of improved heat tolerance rice.

Fine-tuning the activities of ß-KETOACYL-COA SYNTHASE 3 (KCS3) and KCS12 in Arabidopsis is essential for maintaining cuticle integrity.

The plant cuticle, consisting of wax and cutin, is involved in adaptations to various environments. ß-Ketoacyl-CoA synthases (KCSs) usually serve as a component of the fatty acid elongation complex that participates in the production of very long-chain fatty acids and provides precursors for the synthesis of various lipids, including wax; however, we recently reported that KCS3 and KCS12 negatively regulate wax biosynthesis. In this current study, we observed that unlike KCS3-overexpressing (OE) lines, KCS12-OE lines had fused floral organs because of abnormal cuticle biosynthesis. This prompted us to compare the functions of KCS3 and KCS12 during cuticle formation. Mutation of KCS3 caused greater effects on wax production, whereas mutation of KCS12 exerted more severe effects on cutin synthesis. The double-mutant kcs3 kcs12 had significantly increased wax and cutin contents compared to either single-mutant, suggesting that KCS12 and KCS3 have additive effects on cuticle biosynthesis. Cuticle permeability was greater for the double-mutant than for the single mutants, which ultimately led to increased susceptibility to drought stress and floral-organ fusion. Taken together, our results demonstrate the regulatory roles of KCS3 and KCS12 during cuticle biosynthesis, and show that maintaining KCS3 and KCS12 expression at certain levels is essential for the formation of a functional cuticle layer.

Evolution and diversification of CaM/CML gene family in green plants.

Calmodulin (CaM) and calmodulin-like (CML) proteins are crucial Ca2+ sensors, which are widely involved in different biological processes of plants, including their growth and development, and stress responses. However, the origin and evolution of the CaM/CML gene family in plants remain elusive. In this study, 2133 CaM and 23094 CML genes were identified from the 1000 plants project (1 KP) species and the sequenced plants, covering algae, mosses, monilophytes, lycophytes, flowering plants, and all other green plant branches. Analysis showed that the size of the CML subfamily was correlated with the genome size of corresponding plant species, as well as the total gene number in the genome. Moreover, with the evolution from algae to angiosperms, the number of CML genes in plants increased gradually which could have been driven mainly by genome-wide segmental duplication events, while the number of CaMs remained basically stable at 2-3. Phylogenetic analysis demonstrated that CaM first appeared in green algae, while CML appeared earlier and has already been presented in dinoflagellates. Further analysis showed that the number and sequence of EF-hand domain in CaMs are highly conserved, while those of CMLs are diverse among different plant taxa. Expression analysis revealed that the expression level of CaMs was generally higher than that of CMLs, indicating that the high-expression genes have essential functions, while the low-expression genes are the main reasons for the functional diversity of the CaM/CML gene family in plants. The results might contribute to understanding the evolution of CaM/CML genes as well as their molecular functions.

Genetic association between ankylosing spondylitis and major depressive disorders: Shared pathways, protein networks and the key gene.

The prevalence of ankylosing spondylitis (AS) and major depressive disorders (MDD) becomes increasingly pronounced, exerting a significant impact on the life quality of contemporary people. Although there is mounting evidence of a link between AS and major depression disorders, the specific interactions between the two have not been thoroughly investigated. To this end, this study aimed to check whether the gene expression profiles of patients with AS and major depression disorders overlapped, and whether there were any functional links between the identified genes via protein-protein interactions. Herein, the relationship between the 4 datasets (GSE73754, GSE98793, GSE25101, and GSE54564) chosen from the Gene Expression Omnibus for evaluation and validation was investigated using gene characterization and functional enrichment. Then, following Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes that explore the biological processes of common genes and demonstrate the interrelationships between common genes, hub genes were obtained using the STRING database and the application cytoHubba plugin of Cytoscape software. The correlation between the gene and 22 types of immuno-infiltrating cells was explored, and the key gene as well as the diagnostic efficiency of the key gene was obtained through verification. A total of 204 shared genes were discovered, the majority of which were functionally enriched in Ribosome, Coronavirus disease COVID19, Starch and sucrose metabolism, and Galactose metabolism. Then, efforts were made to go through STRING. Immuno-infiltration studies revealed that Neutrophils, T cells CD8, T cells CD4 naive, T cells CD4 memory resting, T cells CD4 memory activated, and T cells regulatory were associated with the pathogenesis of AS and MDD. Additionally, the receiver operating characteristic curve revealed that the key gene MRPL13 played diagnostic roles in AS and MDD after intersecting 10 hub genes with 37 differential expression genes from the 2 validation datasets. The obtained results suggest an overlapping genetic structure between AS and major depression disorders. MRPL13 may provide key insights into the relationship between AS and MDD.

A graphitic-C3N4 derivative containing heptazines merged with phenyls: synthesis, purification and application as a high-efficiency metal-free quasi-green phosphor for white LEDs.

Because rare-earth elements are scarce, expensive, and unsustainable, it is of great significance to develop rare-earth-free (even metal-free) luminescent materials as phosphors for LEDs. Here, a graphitic-C3N4 (g-C3N4) derivative containing some heptazines merged with phenyls has been synthesized via thermal polymerization of melamine and quinazoline-2,4(1H,3H)-dione at an optimal mole ratio of 18 : 1. In comparison with g-C3N4 synthesized from melamine only, the photoluminescent (PL) emission colour changed from blue to green, the maximum emission wavelength (λ em,max) changed from 467 nm to 508 nm, and the PL quantum yield (PLQY) increased from 8.0% to 24.0%. It was further purified via vacuum sublimation, and a product with yellowish green emission (λ em,max = 517 nm) and PLQY up to 45.5% was obtained. This sublimated product had high thermal stability and low thermal quenching; its thermal decomposition temperature was as high as 527 °C, and its relative PL emission intensity at 100 °C was 90.8% of that at 20 °C. Excited by blue light chips (λ em,max ≈ 460 nm), cold, neutral and warm white LEDs can be fabricated using the sublimated product and orange-emitting (Sr,Ba)3SiO5:Eu2+ as phosphors. The good performances of these white LEDs (for example, the CIE coordinates, color rendering index and correlated color temperature were (0.31, 0.33), 84.4 and 6577 K, respectively) suggest that the low-efficiency blue-emitting g-C3N4 had been successfully converted into a high-efficiency metal-free quasi-green phosphor.

An ancestral role for 3-KETOACYL-COA SYNTHASE3 as a negative regulator of plant cuticular wax synthesis.

The plant cuticle, a structure primarily composed of wax and cutin, forms a continuous coating over most aerial plant surfaces. The cuticle plays important roles in plant tolerance to environmental stress, including stress imposed by drought. Some members of the 3-KETOACYL-COA SYNTHASE (KCS) family are known to act as metabolic enzymes involved in cuticular wax production. Here we report that Arabidopsis (Arabidopsis thaliana) KCS3, which was previously shown to lack canonical catalytic activity, instead functions as a negative regulator of wax metabolism by reducing the enzymatic activity of KCS6, a key KCS involved in wax production. We demonstrate that the role of KCS3 in regulating KCS6 activity involves physical interactions between specific subunits of the fatty acid elongation complex and is essential for maintaining wax homeostasis. We also show that the role of the KCS3-KCS6 module in regulating wax synthesis is highly conserved across diverse plant taxa from Arabidopsis to the moss Physcomitrium patens, pointing to a critical ancient and basal function of this module in finely regulating wax synthesis.

Roles of very long-chain fatty acids in compound leaf patterning in Medicago truncatula.

Plant cuticles are composed of hydrophobic cuticular waxes and cutin. Very long-chain fatty acids (VLCFAs) are components of epidermal waxes and the plasma membrane and are involved in organ morphogenesis. By screening a barrelclover (Medicago truncatula) mutant population tagged by the transposable element of tobacco (Nicotiana tabacum) cell type1 (Tnt1), we identified two types of mutants with unopened flower phenotypes, named unopened flower1 (uof1) and uof2. Both UOF1 and UOF2 encode enzymes that are involved in the biosynthesis of VLCFAs and cuticular wax. Comparative analysis of the mutants indicated that the mutation in UOF1, but not UOF2, leads to the increased number of leaflets in M. truncatula. UOF1 was specifically expressed in the outermost cell layer (L1) of the shoot apical meristem (SAM) and leaf primordia. The uof1 mutants displayed defects in VLCFA-mediated plasma membrane integrity, resulting in the disordered localization of the PIN-FORMED1 (PIN1) ortholog SMOOTH LEAF MARGIN1 (SLM1) in M. truncatula. Our work demonstrates that the UOF1-mediated biosynthesis of VLCFAs in L1 is critical for compound leaf patterning, which is associated with the polarization of the auxin efflux carrier in M. truncatula.

The Plant Fatty Acyl Reductases.

Fatty acyl reductase (FAR) is a crucial enzyme that catalyzes the NADPH-dependent reduction of fatty acyl-CoA or acyl-ACP substrates to primary fatty alcohols, which in turn acts as intermediate metabolites or metabolic end products to participate in the formation of plant extracellular lipid protective barriers (e.g., cuticular wax, sporopollenin, suberin, and taproot wax). FARs are widely present across plant evolution processes and play conserved roles during lipid synthesis. In this review, we provide a comprehensive view of FAR family enzymes, including phylogenetic analysis, conserved structural domains, substrate specificity, subcellular localization, tissue-specific expression patterns, their varied functions in lipid biosynthesis, and the regulation mechanism of FAR activity. Finally, we pose several questions to be addressed, such as the roles of FARs in tryphine, the interactions between transcription factors (TFs) and FARs in various environments, and the identification of post-transcriptional, translational, and post-translational regulators.

Two Arabidopsis MYB-SHAQKYF transcription repressors regulate leaf wax biosynthesis via transcriptional suppression on DEWAX.

Plant cuticular wax accumulation limits nonstomatal transpiration and is regulated by external environmental stresses. DEWAX (DECREASE WAX BIOSYNTHESIS) plays a vital role in diurnal wax biosynthesis. However, how DEWAX expression is controlled and the molecular mechanism of wax biosynthesis regulated by the diurnal cycle remains largely unknown. Here, we identified two Arabidopsis MYB-SHAQKYF transcription factors, MYS1 and MYS2, as new regulators in wax biosynthesis and drought tolerance. Mutations of both MYS1 and MYS2 caused significantly reduced leaf wax, whereas overexpression of MYS1 or MYS2 increased leaf wax biosynthesis and enhanced drought tolerance. Our results demonstrated that MYS1 and MYS2 act as transcription repressors and directly suppress DEWAX expression via ethylene response factor-associated amphiphilic repression motifs. Genetic interaction analysis with DEWAX, SPL9 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9), and CER1 (ECERIFERUM 1) in wax biosynthesis and under drought stresses demonstrated that MYS1 and MYS2 act upstream of the DEWAX-SPL9 module, thus regulating CER1 expression. Expression analysis suggested that the diurnal expression pattern of DEWAX is partly regulated by MYS1 and MYS2. Our findings demonstrate the roles of two unidentified transcription repressors, MYS1 and MYS2, in wax biosynthesis and provide insights into the mechanism of diurnal cycle-regulated wax biosynthesis.

Natural variation in root suberization is associated with local environment in Arabidopsis thaliana.

Genetic signature of climate adaptation has been widely recognized across the genome of many organisms; however, the eco-physiological basis for linking genomic polymorphisms with local adaptations remains largely unexplored. Using a panel of 218 world-wide Arabidopsis accessions, we characterized the natural variation in root suberization by quantifying 16 suberin monomers. We explored the associations between suberization traits and 126 climate variables. We conducted genome-wide association analysis and integrated previous genotype-environment association (GEA) to identify the genetic bases underlying suberization variation and their involvements in climate adaptation. Root suberin content displays extensive variation across Arabidopsis populations and significantly correlates with local moisture gradients and soil characteristics. Specifically, enhanced suberization is associated with drier environments, higher soil cation-exchange capacity, and lower soil pH; higher proportional levels of very-long-chain suberin is negatively correlated with moisture availability, lower soil gravel content, and higher soil silt fraction. We identified 94 putative causal loci and experimentally proved that GPAT6 is involved in C16 suberin biosynthesis. Highly significant associations between the putative genes and environmental variables were observed. Roots appear highly responsive to environmental heterogeneity via regulation of suberization, especially the suberin composition. The patterns of suberization-environment correlation and the suberin-related GEA fit the expectations of local adaptation for the polygenic suberization trait.

Fatty alcohol oxidase 3 (FAO3) and FAO4b connect the alcohol- and alkane-forming pathways in Arabidopsis stem wax biosynthesis.

The alcohol- and alkane-forming pathways in cuticular wax biosynthesis are well characterized in Arabidopsis. However, potential interactions between the two pathways remain unclear. Here, we reveal that mutation of CER4, the key gene in the alcohol-forming pathway, also led to a deficiency in the alkane-forming pathway in distal stems. To trace the connection between the two pathways, we characterized two homologs of fatty alcohol oxidase (FAO), FAO3 and FAO4b, which were highly expressed in distal stems and localized to the endoplasmic reticulum. The amounts of waxes from the alkane-forming pathway were significantly decreased in stems of fao4b and much lower in fao3 fao4b plants, indicative of an overlapping function for the two proteins in wax synthesis. Additionally, overexpression of FAO3 and FAO4b in Arabidopsis resulted in a dramatic reduction of primary alcohols and significant increases of aldehydes and related waxes. Moreover, expressing FAO3 or FAO4b led to significantly decreased amounts of C18-C26 alcohols in yeast co-expressing CER4 and FAR1. Collectively, these findings demonstrate that FAO3 and FAO4b are functionally redundant in suppressing accumulation of primary alcohols and contributing to aldehyde production, which provides a missing and long-sought-after link between these two pathways in wax biosynthesis.

A cationic iridium(III) complex containing a thiosemicarbazide unit: Synthesis and application for turn-on chemiluminescent detection of Hg2.

A novel cationic iridium(III) complex [(ppy)2Ir(bPCPC)]PF6 (ppy: 2-phenylpyridine; bPCPC: 2-([2,2'-bipyridine]-4-carbonyl)-N-phenylhydrazinecarbothioamide) containing a thiosemicarbazide unit was designed and synthesized. The thiosemicarbazide unit was a sensitive functional group to Hg2+, when it reacted with Hg2+, it was desulphurized and thus led to the formation of 1,3,4-oxadiazole, [(ppy)2Ir(bPCPC)]PF6 resultantly was used as a "turn-on" chemodosimeter for luminescent detection of Hg2+ in DMF/PBS buffer solution at pH = 7-11. Except for Ag+, recognition capability of [(ppy)2Ir(bPCPC)]PF6 to Hg2+ was not interfered by other common metal ions (Co2+, Li+, Zn2+, Pb2+, K+, Al3+, Na+, Mn2+, Cu2+, Fe2+, Fe3+, Cr3+, Ba2+, Mg2+, Ni2+ and Ca2+). The detection limit was 1.83 × 10-9 mol∙L-1 (0.37 ppb), which indicated the complex was a highly sensitive chemiluminescent detection reagent of Hg2+.

ArabidopsisKCS5 and KCS6 Play Redundant Roles in Wax Synthesis.

3-ketoacyl-CoA synthases (KCSs), as components of a fatty acid elongase (FAE) complex, play key roles in determining the chain length of very-long-chain fatty acids (VLCFAs). KCS6, taking a predominate role during the elongation from C26 to C28, is well known to play an important role in wax synthesis. KCS5 is one paralog of KCS6 and its role in wax synthesis remains unknown. Wax phenotype analysis showed that in kcs5 mutants, the total amounts of wax components derived from carbon 32 (C32) and C34 were apparently decreased in leaves, and those of C26 to C32 derivatives were obviously decreased in flowers. Heterologous yeast expression analysis showed that KCS5 alone displayed specificity towards C24 to C28 acids, and its coordination with CER2 and CER26 catalyzed the elongation of acids exceeding C28, especially displaying higher activity towards C28 acids than KCS6. BiLC experiments identified that KCS5 physically interacts with CER2 and CER26. Wax phenotype analysis of different organs in kcs5 and kcs6 single or double mutants showed that KCS6 mutation causes greater effects on the wax synthesis than KCS5 mutation in the tested organs, and simultaneous repression of both protein activities caused additive effects, suggesting that during the wax biosynthesis process, KCS5 and KCS6 play redundant roles, among which KCS6 plays a major role. In addition, simultaneous mutations of two genes nearly block drought-induced wax production, indicating that the reactions catalyzed by KCS5 and KCS6 play a critical role in the wax biosynthesis in response to drought.

A Chromosome-level Genome Assembly of Wild Castor Provides New Insights into its Adaptive Evolution in Tropical Desert.

Wild castor grows in the high-altitude tropical desert of the African Plateau, a region known for high ultraviolet radiation, strong light, and extremely dry condition. To investigate the potential genetic basis of adaptation to both highland and tropical deserts, we generated a chromosome-level genome sequence assembly of the wild castor accession WT05, with a genome size of 316 Mb, a scaffold N50 of 31.93 Mb, and a contig N50 of 8.96 Mb, respectively. Compared with cultivated castor and other Euphorbiaceae species, the wild castor exhibits positive selection and gene family expansion for genes involved in DNA repair, photosynthesis, and abiotic stress responses. Genetic variations associated with positive selection were identified in several key genes, such as LIG1, DDB2, and RECG1, involved in nucleotide excision repair. Moreover, a study of genomic diversity among wild and cultivated accessions revealed genomic regions containing selection signatures associated with the adaptation to extreme environments. The identification of the genes and alleles with selection signatures provides insights into the genetic mechanisms underlying the adaptation of wild castor to the high-altitude tropical desert and would facilitate direct improvement of modern castor varieties.