Carrot (Daucus carota) is an Apiaceae plant with multi-colored fleshy roots that provides a model system for carotenoid research. In this study, we assembled a 430.40 Mb high-quality gapless genome to the telomere-to-telomere (T2T) level of “Kurodagosun” carrot. In total, 36 268 genes were identified and 34 961 of them were functionally annotated. The proportion of repeat sequences in the genome was 55.3%, mainly long terminal repeats. Depending on the coverage of the repeats, 14 telomeres and 9 centromeric regions on the chromosomes were predicted. A phylogenetic analysis showed that carrots evolved early in the family Apiaceae. Based on the T2T genome, we reconstructed the carotenoid metabolic pathway and identified the structural genes that regulate carotenoid biosynthesis. Among the 65 genes that were screened, 9 were newly identified. Additionally, some gene sequences overlapped with transposons, suggesting replication and functional differentiation of carotenoid-related genes during carrot evolution. Given that some gene copies were barely expressed during development, they might be functionally redundant. Comparison of 24 cytochrome P450 genes associated with carotenoid biosynthesis revealed the tandem or proximal duplication resulting in expansion of CYP gene family. These results provided molecular information for carrot carotenoid accumulation and contributed to a new genetic resource.

Celery is an important leafy vegetable that can grow during the cool season and does not tolerate high temperatures. Heat stress is widely acknowledged as one of the main abiotic stresses affecting the growth and yield of celery. The morphological and physiological indices of celery were investigated in the present study to explore the physiological mechanisms in response to high temperatures. Results showed that the antioxidant enzyme activity, proline, relative conductivity, and malondialdehyde were increased, while chlorophyll and the water content of leaves decreased under high-temperature conditions. Short-term heat treatment increased the stomatal conductance to cool off the leaves by transpiration; however, long-term heat treatment led to stomatal closure to prevent leaf dehydration. In addition, high temperature caused a disordered arrangement of palisade tissue and a loose arrangement of spongy tissue in celery leaves. Combined metabolomic and transcriptomic analyses were further used to reveal the regulatory mechanisms in response to heat stress at the molecular level in celery. A total of 1003 differential metabolites were identified and significantly enriched in amino acid metabolism and the tricarboxilic acid (TCA) cycle. Transcriptome sequencing detected 24,264 different genes, including multiple transcription factor families such as HSF, WRKY, MYB, AP2, bZIP, and bHLH family members that were significantly upregulated in response to heat stress, suggesting that these genes were involved in the response to heat stress. In addition, transcriptional and metabolic pathway analyses showed that heat stress inhibited the glycolysis pathway and delayed the TCA cycle but increased the expression of most amino acid synthesis pathways such as proline, arginine, and serine, consistent with the results of physiological indicators. qRT-PCR further showed that the expression pattern was similar to the expression abundance in the transcriptome. The important metabolites and genes in celery that significantly contributed to the response to high temperatures were identified in the present study, which provided the theoretical basis for breeding heat-resistant celery.

The genus Apium, belonging to the family Apiaceae, comprises roughly 20 species. Only two species, Apium graveolens and Apium leptophyllum, are available in China and are both rich in nutrients and have favorable medicinal properties. However, the lack of genomic data has severely constrained the study of genetics and evolution in Apium plants. In this study, Illumina NovaSeq 6000 and Nanopore sequencing platforms were employed to identify the mitochondrial genomes of A. graveolens and A. leptophyllum. The complete lengths of the mitochondrial genomes of A. graveolens and A. leptophyllum were 263,017 bp and 260,164 bp, respectively, and contained 39 and 36 protein-coding genes, five and six rRNA genes, and 19 and 20 tRNA genes. Consistent with most angiosperms, both A. graveolens and A. leptophyllum showed a preference for codons encoding leucine (Leu). In the mitochondrial genome of A. graveolens, 335 SSRs were detected, which is higher than the 196 SSRs found in the mitochondrial genome of A. leptophyllum. Studies have shown that the most common RNA editing type is C-to-U, but, in our study, both A. graveolens and A. leptophyllum exhibited the U-C editing type. Furthermore, the transfer of the mitochondrial genomes of A. graveolens and A. leptophyllum into the chloroplast genomes revealed homologous sequences, accounting for 8.14% and 4.89% of the mitochondrial genome, respectively. Lastly, in comparing the mitochondrial genomes of 29 species, it was found that A. graveolens, A. leptophyllum, and Daucus carota form a sister group with a support rate of 100%. Overall, this investigation furnishes extensive insights into the mitochondrial genomes of A. graveolens and A. leptophyllum, thereby enhancing comprehension of the traits and evolutionary patterns within the Apium genus. Additionally, it offers supplementary data for evolutionary and comparative genomic analyses of other species within the Apiaceae family.

Celery (Apium graveolens L.) is a kind of green leaf vegetable with a large consumption demand in the food industry. It is a commonly used material in quick-frozen food stuffing such as dumplings and steamed stuffed. Fresh celery leaf blades and petioles are rich in photosynthetic pigments including chlorophyll and carotenoid, their contents are closely related to the quality of celery and its products. In order to explore the effects of freezing and thawing temperature and thawing time on the degradation of photosynthetic pigments in celery leaf blades and petioles, the changes in photosynthetic pigments during thawing storage were measured under different freezing and thawing temperatures. The results showed that lower freezing and thawing temperatures were beneficial to the preservation of photosynthetic pigments in celery leaf blades and petioles, and the loss of photosynthetic pigments enhanced with the increase in thawing temperature and thawing time. Under the cold storage condition of −80 °C, the loss rate of pigment substances can be reduced by nearly 20% compared with that of −18 °C, and −80 °C and 4 °C could be the best temperature combination of freezing and thawing. The content and degradation rate of photosynthetic pigments in celery leaf blades were higher than that in petioles during thawing, with a total chlorophyll loss rate reaching 35% during 6 to 12 h after thawing. The increase in temperature difference between freezing and thawing could aggravate the damage to the cell structure and the degradation of the pigment, as chlorophyll is more sensitive to temperature changes, and the degradation rate is significantly higher than that of carotenoids. From the perspective of delaying the degradation of photosynthetic pigments, the results of this study will provide potential references for the reasonable configuration of freezing and thawing temperatures in the process of storage and transportation of celery products.

There are few reports on the reproductive biology of celery, which produces small flowers in a long flowering period. Anther development was analyzed by paraffin sectioning and related genes were examined by transcriptome sequencing and qPCR. The development process was divided into nine stages based on the significant changes in the cell and tissue morphologies. These stages included: archesporial stage, sporogenous cell stage, microspore mother cell stage, dyad and tetrad stage, mononuclear microspore stage, late uninucleate microspore stage, binuclear cell stage, mature pollen stage, and dehiscence stage. A total of 1074 differentially expressed genes were identified by transcriptome sequencing in the early flower bud, middle flower bud, and early flowering period. Functional annotation indicated that these genes were involved in physiological and biochemical processes such as ribosomes metabolism, sugar metabolism, and amino acid metabolism. Transcription factors such as C2H2, AP2/ERF, bZIP, WRKY, and MYB played key regulatory roles in anther development and had different regulatory capabilities at various stages. The expression patterns based on qPCR and transcriptome data of the selected transcription factor genes showed consistency, suggesting that these genes played an important role in different flower development stages. These results provide a theoretical basis for molecular breeding of new celery varieties with pollen abortion. Furthermore, they have enriched research on the reproductive biology of celery and the Apiaceae family.

The plant mitochondria play a crucial role in various cellular energy synthesis and conversion processes and are essential for plant growth. Watercress (Oenanthe javanica) is a fast-growing vegetable with strong adaptability and wide cultivation range, and it possesses high nutritional value. In our study, we assembled the O. javanica mitochondrial genome using the Illumina and Nanopore sequencing platforms. The results revealed that the mitochondrial genome map of watercress has a circular structure of 384,074 bp, containing 28 tRNA genes, 3 rRNA genes, and 34 protein-coding genes. A total of 87 SSR (simple sequence repeat) loci were detected, with 99% composed of palindrome repeats and forward repeats, while no complementary repeats were identified. Codon preference analysis indicated that watercress prefers to use codons encoding leucine, isoleucine, and serine with a preference for A/U-ending codons. Phylogenetic analysis showed that watercress is closely related to species of Bupleurum, Apium, Angelica, and Daucus, with the closest evolutionary relationship observed with Saposhnikovia divaricata and Apium graveolens. This study provides a valuable resource for the study of the evolution and molecular breeding of watercress.