Strawberry (Fragaria ananassa Duch.) is an economically important crop. Its yield is highly dependent on photosynthesis, and carbon dioxide (CO₂) is one of the most important constituents in photosynthesis. In this study, we investigated the physiological and molecular mechanisms of CO₂ enrichment in increasing strawberry leaf growth, and ultimately fruit yield. Strawberry plants were grown under ambient CO₂ (350–500 μmol/mol) and elevated CO₂ (750–850 μmol/mol) in a controlled environment. The results showed that CO₂ enrichment significantly increased the size, net photosynthetic rate and light saturation point of the leaves, but decreased the light compensation point of leaves. Using RNA sequencing (RNA-Seq), transcriptome profiling of leaf tissues under two CO₂ concentrations was conducted. The analysis identified 150 differentially expressed genes in response to increased CO₂ concentration; 14 of them were shown to be involved in photosynthesis. Gene Ontology (GO) enrichment and pathways analyses revealed that CO₂ enrichment enhanced the biosysthesis of metabolism-promoting growth hormones; sped up the reduction step of CO₂ assimilation, and increased the transport of photosynthetic products, which help explain the increased net photosynthetic rate and accelerated leaf growth under elevated CO₂ level. These results provide a valuable reference for exploring the mechanism of CO₂ application in strawberry production in greenhouses especially during offseason.

Carrot is an important vegetable with roots as the edible organ. A complex regulatory network controls root growth, in which auxin is one of the key players. To clarify the molecular mechanism on auxin regulating carrot root expansion, the growth process and the indole-3-acetic acid (IAA) content in the roots were measured in this experiment. It was found that the rapid expansion period of the root was from 34 to 41 days after sowing and the IAA content was the highest during this period. The root growth then slowed down and the IAA levels decreased. Using the transcriptome sequencing database, we analyzed the expression of IAA-metabolism-related genes and found that the expression of most of the IAA synthesis genes, catabolism genes, and genes related to signal transduction was consistent with the changes in IAA content during root expansion. Among them, a total of 31 differentially expressed genes (DEGs) were identified, including 10 IAA synthesis genes, 8 degradation genes, and 13 genes related to signal transduction. Analysis of the correlations between the DEGs and IAA levels showed that the following genes were closely related to root development: three synthesis genes, YUCCA10 (DCAR_012429), TAR2 (DCAR_026162), and AMI1 (DCAR_003244); two degradation genes, LPD1 (DCAR_023341) and AACT1 (DCAR_010070); and five genes related to signal transduction, IAA22 (DCAR_012516), IAA13 (DCAR_012591), IAA27 (DCAR_023070), IAA14 (DCAR_027269), and IAA7 (DCAR_030713). These results provide a reference for future studies on the mechanism of root expansion in carrots.

Flowering transition is important in plant growth and development, and the SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) gene belongs to the MADS-box gene family, which is an integrator involved in the regulation of flower formation in plants. Current studies have shown that the structural domain of SOC1 is relatively conserved in a variety of plants. To further investigate the function of the SOC1 homologous gene in pak choi, the full-length coding sequence of pak choi BrcSOC1 was cloned, and the structure, subcellular localization and spatiotemporal expression pattern of BrcSOC1 were analyzed in this study. The tissue-specific expression results showed that BrcSOC1 was expressed in roots, leaves, bolts, flowers and pods. The expression results at different developmental stages showed that BrcSOC1 was expressed at the highest level at floral bud differentiation stage 5. When BrcSOC1 was overexpressed in Arabidopsis thaliana, the flowering time in all transgenic plants was significantly earlier than in the wild type, and the expression analysis indicated that BrcSOC1 positively regulated the expression of the downstream genes AGAMOUS-LIKE 24 (AGL24) and LEAFY (LFY). These results provide an important reference for further research on the mechanism of BrcSOC1 in the flowering pathway of pak choi.

Pak choi needs to be exposed to low temperature (vernalized) before flowering will initiate. Early bolting caused by low temperature often occurs in spring and leads to significant economic losses. Therefore, it is of great practical significance to study the flowering process of pak choi. Brassinolide (BR) plays a certain role in the flowering process of pak choi. In order to better understand the role of BR in the flowering process of pak choi, the BR content in the shoot apices of pak choi at different growth stages was determined by enzyme-linked immunosorbent assay (ELISA). The results showed that the BR content increased after low-temperature treatment. With the progress of vegetative growth, the BR content decreased and reached the lowest at 10 days after transplanting (V10), then the content increased and reached a small peak at the critical period of floral bud differentiation (S0). After initiation of floral bud differentiation, the content decreased at floral bud differentiation stage 1 (S1), and then gradually increased and reached a peak at floral bud differentiation stage 3 (S3). In order to clarify the molecular mechanism of BR content changes, we analyzed the expressions of key enzymes coding genes in the BR metabolic pathway, and found that six major synthase-encoding genes (Bra008760, Bra030023, Bra036097, Bra027405, Bra011678, and Bra025409) were upregulated at the critical period of floral bud differentiation, leading to the increase in BR content, which were consistent with changes in the BR content. By analyzing the functions of differentially expressed genes (DEGs) between the vegetative growth stage (V10) and the critical period of floral bud differentiation (S0), 21 DEGs were found to be related to BR metabolism. These findings can provide a reference for elucidating the molecular mechanism of BR regulating the flowering process of pak choi.

Elevated CO₂ can affect the synthesis and distribution of photosynthetic assimilates. However, the carbohydrate metabolism molecular mechanism of cucumber leaves in response to CO₂ enrichment is unclear. Therefore, it is of great significance to investigate the key functional regulatory genes in cucumber. In this study, the growth of cucumber leaves under different CO₂ conditions was compared. The results showed that under CO₂ enrichment, leaf area increased, the number of mesophyll cells increased, stomata enlarged, and more starch grains accumulated in the chloroplasts. Compared with the control, the starch and soluble sugar content of leaves were maximally increased by 194.1% and 55.94%, respectively; the activities of fructose-1,6-bisphosphatase (FBPase), ADPG pyrophosphorylase (AGPase), starch synthase (SSS), sucrose phosphate synthase (SPS), sucrose synthase (SS) and invertase (Inv) were maximally increased by 36.91%, 66.13%, 33.18%, 21.7%, 54.11%, and 46.01%, respectively. Through transcriptome analysis, a total of 1,582 differential expressed genes (DEGs) were identified, in which the starch and sucrose metabolism pathway was significantly enriched, and 23 genes of carbon metabolism were screened. Through metabolome analysis, a total of 22 differential accumulation metabolites (DAMs) were identified. Moreover, D-glucose and D(+)-glucose were significantly accumulated, showing upregulation 2.4-fold and 2.6-fold, respectively. Through combined analysis of transcriptome and metabolome, it was revealed that seven genes were highly related to D-glucose, and Csa6G153460 (AGPase), Csa5G612840 (β-glucosidase), and Csa4G420150 (4-α-glucanotransferase) were significantly correlated to the carbohydrate regulatory network. Furthermore, the mechanism of CO₂ enrichment that promotes carbohydrate metabolism in leaves at the molecular level was revealed. This mechanism advances the development of the cell wall and leaf morphology by activating the expression of key genes and improving enzyme activity.