Drought priming at seedling stage improves photosynthetic performance and yield of potato exposed to a short-term drought stress.

Potato (Solanum tuberosum L.) is an important food and vegetable crop worldwide. In recent years, the arid environment resulting from climate change has caused a sharp decline in potato yield. To clarify the effect of drought priming at the seedling stage on the tolerance of potato plants to drought stress during tuber expansion, we conducted a pot experiment to investigate the physiological response of the plants generated from seed potatoes of the variety 'Favorita' to varied water supply conditions: normal water supply at the seedling stage (control), normal water supply at the seedling stage and drought stress at the mid-tuber-expansion stage (non-primed), and drought priming at the seedling stage plus drought stress at the mid-tuber-expansion stage (primed). Drought priming resulted in an increase in the number of small vascular bundles in potato plants compared to non-primed plants. It also altered the shape and density of stomata, enhancing water use efficiency and reducing whole-plant transpiration. The primed plants maintained the basal stem cambium for a longer time under drought stress, which gained an extended differentiation ability to generate a greater number of small vascular bundles compared to non-primed plants. Drought priming increased the amount and rate of dry matter translocation, and so reduced the adverse effects on tubers of potato under drought stress. Therefore, drought priming at the seedling stage improved the photosynthetic performance and yield, and probably enhanced the drought tolerance of potato.

Systematic Analysis of Galactinol Synthase and Raffinose Synthase Gene Families in Potato and Their Expression Patterns in Development and Abiotic Stress Responses.

Raffinose family oligosaccharides (RFOs) are very important for plant growth, development, and abiotic stress tolerance. Galactinol synthase (GolS) and raffinose synthase (RFS) are critical enzymes involved in RFO biosynthesis. However, the whole-genome identification and stress responses of their coding genes in potato remain unexplored. In this study, four StGolS and nine StRFS genes were identified and classified into three and five subgroups, respectively. Remarkably, a total of two StGolS and four StRFS genes in potato were identified to form collinear pairs with those in both Arabidopsis and tomato, respectively. Subsequent analysis revealed that StGolS4 exhibited significantly high expression levels in transport-related tissues, PEG-6000, and ABA treatments, with remarkable upregulation under salt stress. Additionally, StRFS5 showed similar responses to StGolS4, but StRFS4 and StRFS8 gene expression increased significantly under salt treatment and decreased in PEG-6000 and ABA treatments. Overall, these results lay a foundation for further research on the functional characteristics and molecular mechanisms of these two gene families in response to ABA, salt, and drought stresses, and provide a theoretical foundation and new gene resources for the abiotic-stress-tolerant breeding of potato.

Ectopic Expression of BcCUC2 Involved in Sculpting the Leaf Margin Serration in Arabidopsis thaliana.

Leaf margin serration is a morphological characteristic in plants. The CUC2 (CUP-SHAPED COTYLEDON 2) gene plays an important role in the outgrowth of leaf teeth and enhances leaf serration via suppression of growth in the sinus. In this study, we isolated the BcCUC2 gene from Pak-choi (Brassica rapa ssp. chinensis), which contains a 1104 bp coding sequence, encoding 367 amino acid residues. Multiple sequence alignment exhibited that the BcCUC2 gene has a typical conserved NAC domain, and phylogenetic relationship analysis showed that the BcCUC2 protein has high identity with Cruciferae plants (Brassica oleracea, Arabidopsis thaliana, and Cardamine hirsuta). The tissue-specific expression analysis displayed that the BcCUC2 gene has relatively high transcript abundance in floral organs. Meanwhile, the expression profile of BcCUC2 was relatively higher in the '082' lines with serrate leaf margins than the '001' lines with smooth leaf margins in young leaves, roots, and hypocotyls. In addition, the transcript level of BcCUC2 was up-regulated by IAA and GA3 treatment, especially at 1-3 h. The subcellular localization assay demonstrated that BcCUC2 was a nuclear-target protein. Furthermore, leaf serration occurred, and the number of the inflorescence stem was increased in the transgenic Arabidopsis thaliana plants' overexpressed BcCUC2 gene. These data illustrated that BcCUC2 is involved in the development of leaf margin serration, lateral branches, and floral organs, contributing to further uncovering and perfecting the regulation mechanism of leaf serration in Pak-choi.

Transcriptome analysis reveals the proline metabolic pathway and its potential regulation TF-hub genes in salt-stressed potato.

Potato (Solanum tuberosum) is currently the third most important food crop in the world. However, the production of potato is seriously threatened by salt stress, which often occurs in the facility cultivation environment, and the mining of salt tolerance genes in potato remains to be further studied. In this study, test-tube plantlets of DM potato were treated with 200-mM NaCl to simulate salt stress, and 15 cDNA libraries were constructed for RNA-seq analysis. A total of 8383 DEGs were identified, of which 3961 DEGs were shared among all the salt treatments, and 264 (7.15%) TF-coding genes were identified from these shared DEGs. KEGG enrichment analysis showed that most DEGs identified from the "arginine and proline metabolism" (ko00330) were enriched in the proline metabolic pathway, and their functions almost covered the whole proline metabolic process. Further analysis showed that expression levels of all the 13 structural DEGs in the pathway were significantly up-regulated and proline accumulation was also significantly increased under salt stress, and 13 TF-hub genes were discovered by WGCNA in the lightcyan and tan modules which were highly positively correlated with the proline contents. Correlation analysis revealed that the four TF-hub genes of the lightcyan module and seven structural DEGs of the proline metabolic pathway might be the potential candidate genes, especially the potential and novel regulatory gene StGLK014720. Furthermore, the dual-luciferase reporter assay confirmed that the key protein StGLK014720 could activate the promoters of both structural genes StAST021010 and StAST017480. In conclusion, these results lay the foundation for further study on the salt tolerance mechanism of potato, and provide a theoretical basis and new genetic resources for salt tolerance breeding of potato.

Overexpression of a Pak Choi Gene, BcAS2, Causes Leaf Curvature in Arabidopsis thaliana.

The LBD (Lateral Organ Boundaries Domain) family are a new group of plant-specific genes, which encode a class of transcription factors containing conserved Lateral Organization Boundary (LOB) domains, and play an important role in regulating the adaxial-abaxial polarity of plant leaves. In Arabidopsis thaliana, ASYMMETRIC LEAVES 2 (AS2) has a typical LOB domain and is involved in determining the adaxial cell fate. In this study, we isolated the BcAS2 gene from the pak choi cultivar "NHCC001", and analyzed its expression pattern. The results showed that the BcAS2 encoded a protein made up of 202 amino acid residues which were located in the nucleus and cytomembrane. The Yeast two-hybrid system (Y2H) assay indicated that BcAS2 interacts with BcAS1-1 and BcAS1-2 (the homologous genes of AS1 gene in pak choi). In the transgenic Arabidopsis thaliana that overexpressed BcAS2 gene, it presented an abnormal phenotype with a curly shape. Taken together, our findings not only validate the function of BcAS2 in leaf development in Arabidopsis thaliana, but also contribute in unravelling the molecular regulatory mechanism of BcAS2, which fulfills a special role by forming complexes with BcAS1-1/2 in the establishment of the adaxial-abaxial polarity of the lateral organs in pak choi.

Cloning and Functional Analysis of BcMYB101 Gene Involved in Leaf Development in Pak Choi (Brassica rapa ssp. Chinensis).

As one of the largest transcription factor families, MYB transcription factors are widely present, and they are involved in a diverse range of physiological activities in plants, such as leaf development. GAMYB genes belong to the R2R3-MYB subfamily, which includes the MYB33/65/101 gene, and these genes are studied well in seed germination and flowering, but their roles in leaf development are poorly understood. In the current study, we isolated a GAMYB transcription factor from pak choi, BcMYB101, and analyzed its characteristics and function. The sequence structure analysis indicated that BcMYB101 has a highly conserved R2R3 DNA-binding domain in the N-terminal region and three GAMYB-specific motifs (Box1, Box2, and Box3). The expression pattern of diverse tissues revealed that BcMYB101 has a higher transcript level in the petiole, leaf, root, and floral organs. Furthermore, the expression level was significantly elevated after GA (gibberellin) treatment, suggesting that the BcMYB101 response was positively regulated by GA. Subcellular localization exhibited that BcMYB101 was only present in the nuclear region, consistent with the characterization of the transcription factor. The overexpression of BcMYB101 elucidated that BcMYB101 increased leaf number and resulted in downward-curling cauline leaves. Moreover, the virus-induced BcMYB101 silencing displayed that BcMYB101 is involved in the regulation of curly leaves. Furthermore, we discovered that BcMYB101 has two trans-activation activities and one interaction protein, BcTCH4, using a trans-activation activity assay and a yeast two-hybrid assay, respectively. In this study, we firstly isolated the BcMYB101 gene and explored its function in leaf development, thereby providing a solid foundation for further research on the regulatory mechanism of leaf shape in Brassica or other species.

Ectopic Expression of a Pak-choi YABBY Gene, BcYAB3, Causes Leaf Curvature and Flowering Stage Delay in Arabidopsis thaliana.

The YABBY family are a group of seed plant-specific transcription factors, which are involved in the specification of abaxial polarity in lateral organs. In Arabidopsis thaliana, YABBY3 (YAB3) plays a critical role in regulating abaxial patterning, growth of lateral organs, and inflorescence phyllotaxy. In this study, the BcYAB3 gene was isolated from Pak-choi (Brassica rapa subsp. chinensis). The tissue-specific expression analysis indicated that the BcYAB3 gene has significantly high transcript levels in stem, leaf, and flower. We investigated the subcellular localization of BcYAB3 and found the protein to be expressed in the nucleus. In the transgenic Arabidopsisthaliana plants expressing the BcYAB3 gene, the leaves were curling downward with the plant growth, and the bolting and flowering stages were delayed. These results not only validate the function of BcYAB3 in the leaf and flower development in Arabidopsis, but also contribute to unravel the molecular regulatory mechanism of YAB3 gene in the establishment of adaxial-abaxial polarity of the lateral organs in Pak-choi.