Identification of QTLs and Putative Candidate Gene Involved in Rhizome Enlargement of Asian lotus (Nelumbo Nucifera)

Lotus (Nelumbo) is perennial aquatic plant with nutritional, pharmacological, and ornamental significance. Rhizome is an underground lotus stem that act as a storage organ and as a reproductive tissue for asexual production. The enlargement of lotus rhizome is an important adaptive strategy for surviving the cold winter. The aims of this study were to identify quantitative trait loci (QTLs) for rhizome enlargement traits including rhizome enlargement index (REI) and number of enlarged rhizome (NER), and to uncover candidate genes associated with these phenotypic traits. A high-density genetic linkage map was constructed, consisting of 2,935 markers binned from 236,840 SNPs. A total of 14 significant QTLs were detected for REI and NER, which explained 6.67–22.28% of trait variance. Three QTL regions were repeatedly identified in at least two years, and a major QTL, designated cqREI-LG2, with a rhizome-enlargement effect and about 20% of the phenotypic contribution was identified across the three climatic years. A candidate NnBEL6 gene located within the confidence interval of cqREI-LG2 was considered to be putatively involved in lotus rhizome enlargement. The expression of NnBEL6 was exclusively induced by rhizome swelling. Sequence comparison of NnBEL6 among lotus varieties revealed a functional Indel site in its promoter that likely initiates the rhizome enlargement process. Transgenic potato assay was used to confirm the role of NnBEL6 in inducing tuberization. The successful identification QTLs and functional validation of NnBEL6 gene reported in this study will enrich our knowledge on the genetic basis of rhizome enlargement in lotus.

Overexpression of Galactinol Synthase 1 From Solanum Commersonii (ScGolS1) Confers Freezing Tolerance In Transgenic Potato

Potato (Solanum tuberosum L.) is the fourth largest food crop in the world. Low temperature causes serious damage to potato plants every year, and freezing tolerance has become a hot spot in potato research. Galactinol synthase (GolS) is a key enzyme in the synthesis of raffinose family oligosaccharides (RFOs), and plays an important role in the response of plants to abiotic stress. In this study, the ScGolS1 gene from S. commersonii was cloned and introduced into the S. tuberosum cultivars ‘Atlantic’ and ‘Desiree’ via Agrobacterium-mediated transformation. Phenotyping assay showed that overexpression of the ScGolS1 could significantly improve freezing tolerance in transgenic potato plants. Further physiological and biochemical results showed that the relative conductivity, malondialdehyde (MDA) content, and 3,3'-Diaminobenzidine (DAB) staining of the transgenic lines decreased, and the plant survival rate increased compared with wild type (WT). Moreover, CBF1, CBF2, CBF3, CBF downstream cold responsive genes COR413, COR47 and ERF transcription factor genes ERF3, ERF4, ERF6 in the ethylene signaling pathway were all induced by freezing treatment, while higher levels were observed in ScGolS1 overexpression lines compared with WT. In addition, other genes such as MIPS, STS and RS genes from RFO metabolic pathway and some sugars content were altered in response to freezing treatment. This indicates that overexpression of the ScGolS1 gene induced both the regulation of the ethylene signaling pathway and the metabolism of raffinose series oligosaccharides, regulating the balance of sugar composition and improved anti-peroxidation capacity, and thereby improved freezing tolerance in potato. These results provide theoretical support and genetic resources for freezing tolerance breeding in potato.

Comparative Phenotypic and Agronomic Assessment of Transgenic Potato with 3R-Gene Stack with Complete Resistance to Late Blight Disease

Transgenic potato event Vic.172, expressing three naturally occurring resistance genes (R genes) conferring complete protection against late blight disease, was evaluated for resistance to late blight, phenotypic characterization, and agronomic performance in field conditions at three locations during three seasons in Uganda. These trials were conducted by comparison to the variety Victoria from which Vic.172 derives, using identical fungicide treatment, except when evaluating disease resistance. During all seasons, the transgenic event Vic.172 was confirmed to have complete resistance to late blight disease, whereas Victoria plants were completely dead by 60–80 days after planting. Tubers from Vic.172 were completely resistant to LB after artificial inoculation. The phenotypic characterization included observations of the characteristics and development of the stems, leaves, flowers, and tubers. Differences in phenotypic parameters between Vic.172 and Victoria were not statistically significant across locations and seasons. The agronomic performance observations covered sprouting, emergence, vigor, foliage growth, and yield. Differences in agronomic performance were not statistically significant except for marketable yield in one location under high productivity conditions. However, yield variation across locations and seasons was not statistically significant, but was influenced by the environment. Hence, the results of the comparative assessment of the phenotype and agronomic performance revealed that transgenic event Vic.172 did not present biologically significant differences in comparison to the variety Victoria it derives from.

The Overexpression of The VvWRKY2 Transcription Factor in Potato Improved the Agricultural Performance and Tubers’ Physio-Chemical and Industrial Properties Even Under Non‐Stress Conditions

The tryptophan-arginine-lysine-tyrosine (WRKY) transcription factors play important roles in plant growth and response to biotic and abiotic stresses. Several studies described WRKY factors overexpression in different plant species. In a number of cases, modification in morphology and seed size were described in transgenic plants overexpressing transcription factors from this family. In this work, we aimed to study the effect of a grapevine VvWRKY2 transcription factor on transgenic potato plants growth, yields and chemical properties of tubers produced out of any stress condition in the greenhouse and in the field. The results were compared with the wild type commercial variety "Belle de Fontenay" (WT). Data showed that the overexpression of the VvWRKY2 transcription factor increased significantly the leaf area and stem diameter of transgenic plants in comparison to WT. A modification of leaf shape was also noticed in VvWRKY2 overexpressing potato plants. The tuber yield, caliber, dry matter, starch and mineral content of transgenic tubers was higher than WT, while soluble sugars level decreased. All these results suggest that the VvWRKY2 overexpression in potato plants seems to have positive effect on plant vigor, yield and tuber quality under normal conditions in addition to its positive effect on plant response to stresses.

Obtaining of transgenic potato (Solanum tuberosum L.) cultivar IPB CP3 containing LYZ‐C gene resistant to bacterial wilt disease

Bacterial wilt caused by Ralstonia solanacearum is one of the most important bacterial diseases in potato production. This study aimed to obtain the transgenic potato (Solanum tuberosum L.) cultivar IPB CP3, containing LYZ‐C gene encoding for lysozyme type C, resistant to bacterial disease caused by R. solanacearum. Genetic transformation using Agrobacterium tumefaciens LBA4404 to 124 internode explants resulted in the transformation efficiency of about 47.58% with a regeneration efficiency of approximately 30.51%. Gene integration analysis showed that 16 clones were confirmed as transgenic clones containing the LYZ‐C gene. Analysis of resistance to R. solanacearum of three transgenic clones showed that all three transgenic clones were more resistant than a non‐transgenic one. This result showed that the LYZ‐C gene integrated in the genome of transgenic potato increased the resistance of potato plants to R. solanacearum. We obtained two transgenic clones considered resistant to bacterial wilt disease.

StPIP1, a PAMP-induced peptide in potato, elicits plant defenses and is associated with disease symptom severity in a compatible interaction with Potato virus Y

The role of small secreted peptides in plant defense responses to viruses has seldom been investigated. Here, we report a role for potato (Solanum tuberosum) PIP1, a gene predicted to encode a member of the pathogen-associated molecular pattern (PAMP)-induced peptide (PIP) family, in the response of potato to Potato virus Y (PVY) infection. We show that exogenous application of synthetic StPIP1 to potato leaves and nodes increased the production of reactive oxygen species and the expression of plant defense-related genes, revealing that StPIP1 triggers early defense responses. In support of this hypothesis, transgenic potato plants that constitutively overexpress StPIP1 had higher levels of leaf callose deposition and, based on measurements of viral RNA titers, were less susceptible to infection by a compatible PVY strain. Interestingly, systemic infection of StPIP1-overexpressing lines with PVY resulted in clear rugose mosaic symptoms that were absent or very mild in infected non-transgenic plants. A transcriptomics analysis revealed that marker genes associated with both pattern-triggered immunity and effector-triggered immunity were induced in infected StPIP1 overexpressors but not in non-transgenic plants. Together, our results reveal a role for StPIP1 in eliciting plant defense responses and in regulating plant antiviral immunity.