Many lncRNAs have been shown to play a vital role in aging processes. However, how lncRNAs regulate seed aging remains unknown. In this study, we performed whole transcriptome strand-specific RNA sequencing of samples from rice embryos, analyzed the differences in expression of rice seed lncRNAs before and after artificial aging treatment (AAT), and systematically screened 6002 rice lncRNAs. During the AAT period, the expression levels of most lncRNAs (454) were downregulated and only four were upregulated among the 458 differentially expressed lncRNAs (DELs). Cis- or trans-regulated target genes of the four upregulated lncRNAs were mainly related to base repair, while 454 downregulated lncRNAs were related to plant–pathogen interaction, plant hormones, energy metabolism, and secondary metabolism. The pathways of DEL target genes were similar with those of differentially expressed mRNAs (DEGs). A competing endogenous RNA (ceRNA) network composed of 34 lncRNAs, 24 microRNAs (miRNA), and 161 mRNAs was obtained. The cDNA sequence of lncRNA LNC_037529 was obtained by rapid amplification of cDNA ends (RACE) cloning with a total length of 1325 bp, a conserved 5′ end, and a non-conserved 3′ end. Together, our findings indicate that genome-wide selection for lncRNA downregulation was an important mechanism for rice seed aging. LncRNAs can be used as markers of seed aging in rice. These findings provide a future path to decipher the underlying mechanism associated with lncRNAs in seed aging.

A species of Cardamine circaeoides Hook. f. et Thoms., 1861, which belongs to the Cardamine family (Brassicaceae), is an endemic species of the Wuling Mountains in Hunan and Hubei Provinces of China. Since there are many morphologically related species of C. circaeoides, the chloroplast (cp) genome characteristics of C. circaeoides were analyzed in order to explore the phylogenetic relationship between it and the closely related species. A cp genome totaling 154,838 base pairs exhibited a typical quadripartite structure with a pair of IRs (inverted repeats; 26,493 base pairs) separated by a small single-copy region of 17,938 base pairs and a large single-copy region of 83,914 base pairs. A total of 130 genes were found in the cp genome, including 85 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. There were 36.21%, 33.96%, 29.09%, and 42.35% GC content in the entire cp genome, LSC region, SSC region, and IR region, respectively. According to phylogenetic analysis, C. circaeoides is evolutionarily closer to Cardamine hupingshanensis.

Metasequoia glyptostroboides, Hu and W. C. Cheng, as the only surviving relict species of the Taxodiaceae Metasequoia genus, is a critically endangered and protected species in China. There is a risk of extinction due to the low vigor of M. glyptostroboides seeds, and the physiological mechanism of seed aging in M. glyptostroboides is not yet clear. In order to investigate the physiological and molecular mechanisms underlying the aging process of M. glyptostroboides seeds, we analyzed the antioxidant system and transcriptome at 0, 2, 4, 6, and 8 days after artificial accelerated aging treatment at 40 °C and 100% relative humidity. It was found that the germination percentage of fresh dried M. glyptostroboides seeds was 54 ± 5.29%, and significantly declined to 9.33 ± 1.88% after 6 days of aging, and then gradually decreased until the seed died on day 8. Superoxide dismutase (SOD) activity, ascorbic acid (AsA), glutathione (GSH) content and superoxide anion (O₂^·−) content and production rate significantly decreased, while malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content and glutathione peroxidase (GPX) and catalase (CAT) activity gradually increased during the aging process. A total of 42,189 unigenes were identified in the whole transcriptome, and 40,446 (95.86%) unigenes were annotated in at least one protein database. A total of 15,376 differentially expressed genes (DEGs) were obtained; KEGG enrichment analysis results revealed that seed aging may be mainly involved in the protein-processing pathways in endoplasmic reticulum, oxidative phosphorylation, and ascorbate and aldarate metabolism. Weighted gene co-expression network analysis (WGCNA) revealed that the dark magenta, orange, and medium purple modules were highly correlated with physiological indicators such as SOD, CAT, and GSH and further identified 40 hub genes such as Rboh, ACO, HSF, and CML as playing important roles in the antioxidant network of M. glyptostroboides seeds. These findings provide a broader perspective for studying the regulatory mechanism of seed aging and a large number of potential target genes for the breeding of other endangered gymnosperms.

The seeds of Metasequia glyptostroboides Hu et Cheng, an endangered species, are susceptible to aging, making natural population renewal difficult and increasing the risk of extinction. LncRNAs play important roles in plant growth and development and biotic and abiotic stress responses, but the functions of lncRNAs in the aging process of M. glyptostroboides seeds are still unclear. In this study, we used single molecule real-time (SMRT) sequencing technology in combination with Illumina RNA-seq to analyze lncRNA changes during M. glyptostroboides seed aging. We identified 403 intergenic lncRNAs (lincRNAs), 29 intronic lncRNAs, and 25 antisense lncRNAs; screened 9000 differentially expressed mRNAs (DEGs) and 128 differentially expressed lncRNAs (DELs); and predicted 844 cis-target genes and 8098 trans-target genes. GO and KEGG functional annotation of target genes revealed that the regulation of the reactive oxygen species metabolic process, protein processing in the endoplasmic reticulum, and the MAPK signaling pathway and other pathways were significantly enriched, showing a high correlation with the mRNA enrichment results. In addition, we constructed a ceRNA network consisting of 18 lncRNAs, 38 miRNAs, and 69 mRNAs, in which some miRNAs and mRNAs related to seed aging were found. Among them, miR167(a,b,c,d) may compete with lncRNA_00185, which is related to plant aging, to regulate the expression of the RCD1(Radical-induced Cell Death1) gene, thus promoting the balance of seed reactive oxygen species and enhancing seed-aging resistance. These results will have significant reference value in elucidating the molecular mechanism of the seed aging of M. glyptostroboides sequoia, improving the storage capacity for crop seeds, and protecting rare germplasm resources.

Sophora tonkinensi is a shrub of the genus Sophora in the family Fabaceae with anti-inflammatory and pain-relieving effects. While the cultivation, chemical makeup, and medicinal properties of S. tonkinensis have been reported, the physiological mechanisms governing its dehydration and cryopreservation tolerance of seeds remain unclear. In this study, we investigated the morphological, physiological, biochemical, and protein expression characteristics of S. tonkinensis seeds subjected to dehydration and cryopreservation techniques via the observation of cell microstructure, determination of antioxidant enzyme activity, and iTRAQ-based proteomic analysis, respectively. The results of the study demonstrated that the seeds possessed a certain level of tolerance to dehydration. The highest germination percentage of 83.0% was observed after 2 h of dehydration (10.1% water content), which was identified as the optimal time point for cryopreservation. However, the germination percentage was reduced to only 30.5% when the water content reached 5.4%, indicating that S. tonkinensis seeds exhibit intermediate storage behavior. Further investigation revealed that during seed dehydration and cryopreservation treatment, liposomes were gradually and highly fused, whereas the activities of ROS scavenging and stress defense were significantly enhanced. During dehydration, the seed tissues formed a protective mechanism of stress resistance based on protein processing in the endoplasmic reticulum and antioxidant system, which was related to the dehydration tolerance. Moreover, only three differentially expressed LEA proteins were identified, and it is speculated that the strengthening of intracellular metabolism and the absence of specific LEA and dehydrins could be crucial factors for the reduced germination percentage after excessive dehydration and cryopreservation.

Nekemias cantoniensis (Hook. et Arn.) Planch 1873 is a woody vine species native to South and Southwest China that is rich in flavonoids and also displays excellent pharmacological activities. The purpose of this study was to characterize the complete chloroplast (cp) genome of N. cantoniensis using Illumina pair-end sequencing data. In summary, the complete cp genome of N. cantoniensis exhibits a quadripartite structure with a length of 162,655 base pairs, including a large single-copy (LSC) region of 89,341 base pairs, a small single-copy (SSC) region of 19,076 base pairs, and two inverted repeats (IRs) regions of 27,119 base pairs. The overall GC content of the genome is 37.41%, while the corresponding values for the LSC, SSC, and IR regions are 34.75%, 32.89%, and 43.02%, respectively. The genome contains 137 genes, of which 87 are protein coding, 36 are tRNA coding, and eight are rRNA coding. Maximum-likelihood phylogenetic analyses revealed that N. cantoniensis was clustered with N. grossedentata.