Improving Agrobacterium tumefaciens−Mediated Genetic Transformation for Gene Function Studies and Mutagenesis in Cucumber (Cucumis sativus L.)

In the post−genomics era, Agrobacterium tumefaciens−mediated genetic transformation is becoming an increasingly indispensable tool for characterization of gene functions and crop improvement in cucumber (Cucumis sativus L.). However, cucumber transformation efficiency is still low. In this study, we evaluated the effects of several key factors affecting the shoot−regeneration rate and overall transformation efficiency in cucumber including genotypes, the age and sources of explants, Agrobacterium strains, infection/co−cultivation conditions, and selective agents. We showed that in general, North China cucumbers exhibited higher shoot−regeneration rate than US pickling or slicing cucumbers. The subapical ground meristematic regions from cotyledons or the hypocotyl had a similar shoot−regeneration efficiency that was also affected by the age of the explants. Transformation with the Agrobacterium strain AGL1 yielded a higher frequency of positive transformants than with GV3101. The antibiotic kanamycin was effective in selection against non−transformants or chimeras. Optimization of various factors was exemplified with the development of transgenic plants overexpressing the LittleLeaf (LL) gene or RNAi of the APRR2 gene in three cucumber lines. The streamlined protocol was also tested in transgenic studies in three additional genes. The overall transformation efficiency defined by the number of verified transgenic plants out of the number of seeds across multiple experiments was 0.2–1.7%. Screening among T1 OE transgenic plants identified novel, inheritable mutants for leaf or fruit color or size/shape, suggesting T−DNA insertion as a potential source of mutagenesis. The Agrobacterium−mediated transformation protocol from this study could be used as the baseline for further improvements in cucumber transformation.

Fine genetic mapping of the Mottled Rind Color (Morc) locus reveals a 4895-bp presence-absence variation contributing to the mottled or unmottled fruit rind color in cucumber

Genomic insights into the evolutionary history and diversification of bulb traits in garlic

Abstract Background Garlic is an entirely sterile crop with important value as a vegetable, condiment, and medicine. However, the evolutionary history of garlic remains largely unknown. Results Here we report a comprehensive map of garlic genomic variation, consisting of amazingly 129.4 million variations. Evolutionary analysis indicates that the garlic population diverged at least 100,000 years ago, and the two groups cultivated in China were domesticated from two independent routes. Consequently, 15.0 and 17.5% of genes underwent an expression change in two cultivated groups, causing a reshaping of their transcriptomic architecture. Furthermore, we find independent domestication leads to few overlaps of deleterious substitutions in these two groups due to separate accumulation and selection-based removal. By analysis of selective sweeps, genome-wide trait associations and associated transcriptomic analysis, we uncover differential selections for the bulb traits in these two garlic groups during their domestication. Conclusions This study provides valuable resources for garlic genomics-based breeding, and comprehensive insights into the evolutionary history of this clonal-propagated crop.

Agrobacterium Tumefaciens-Mediated Genetic Transformation in Cucumber

LITTLELEAF ( LL ) encodes a WD40 repeat domain‐containing protein associated with organ size variation in cucumber

SummaryPlants employ tight genetic control to integrate intrinsic growth signals and environmental cues to enable organs to grow to a defined size. Many genes contributing to cell proliferation and/or cell expansion, and consequently organ size control, have been identified, but the regulatory pathways are poorly understood. Here we have characterized a cucumber littleleaf (ll) mutant which exhibits smaller organ sizes but more lateral branches than the wild type. The small organ size in ll was due to a reduction of both cell number and cell size. Quantitative trait locus (QTL) analyses revealed co‐localization of major‐effect QTLs for fruit size, fruit and seed weight, as well as number of lateral branches, with the LL locus indicating pleiotropic effects of the ll mutation. We demonstrate that LL is an ortholog of Arabidopsis STERILE APETALA (SAP) encoding a WD40 repeat domain‐containing protein; the mutant protein differed from the wild type by a single amino acid substitution (W264G) in the second WD40 repeat. W264 was conserved in 34 vascular plant genomes examined. Phylogenetic analysis suggested that LL originated before the emergence of flowering plants but was lost in the grass genome lineage. The function of LL in organ size control was confirmed by its overexpression in transgenic cucumbers and ectopic expression in Arabidopsis. Transcriptome profiling in LL and ll bulks revealed a complex regulatory network for LL‐mediated organ size variation that involves several known organ size regulators and associated pathways. The data support LL as an important player in organ size control and lateral branch development in cucumber.

Mutations in CsPID encoding a Ser/Thr protein kinase are responsible for round leaf shape in cucumber (Cucumis sativus L.)

Identification and functional characterization of APRR2 controlling green immature fruit color in cucumber (Cucumis sativus L.)

Map-based cloning, identification and characterization of the w gene controlling white immature fruit color in cucumber (Cucumis sativus L.)

Round fruit shape in WI7239 cucumber is controlled by two interacting quantitative trait loci with one putatively encoding a tomato SUN homolog

Fine genetic mapping of the white immature fruit color gene w to a 33.0-kb region in cucumber (Cucumis sativus L.)

The effect of cultivar, sowing date and transplant location in field on bolting of Welsh onion (Allium fistulosumL.)

Abstract Background Bolting reduces the quality and commercial yield of Welsh onion (Allium fistulosum L.) in production. However, seed production is directly dependent on flower induction and bolting. The Welsh onion belongs to the green plant vernalisation type, specific seedling characteristics and sufficient accumulated time at low temperature are indispensible for the completion of its vernalisation process. Only if these conditions for vernalisation are fulfilled, the plants will bolt in the following year. The present investigation evaluated the effects of cultivar, sowing date and transplant location in field on the bolting of Welsh onion at the Horticultural Farm of the College of Horticulture, Northwest A&F University, Yangling, Shannxi Province, China in two succeeding production years: 2010–2011 and 2011–2012. A strip split plot layout within a randomised complete block design with three replications was used. Results The results revealed that all three factors (cultivar, sowing date and transplant location) and their interaction had significant effects on the initiation and final rate of bolting observed by 30 April. The earliest bolting date (14 February, 2011 and 15 February, 2012) and the highest bolting rate (100% in 2011 and 62% in 2012) occurred when the JinGuan cultivar was sown on 20 August and transplanted in a plastic tunnel, whereas the latest date and lowest rate (no bolting observed until 30 April) of bolting occurred when the XiaHei cultivar was sown on 29 September and transplanted in an open field. Conclusions These results suggest that we can control bolting in Welsh onion production by choosing an appropriate cultivar, sowing date and transplant location. Choosing a late bolting cultivar, such as cultivar XiaHei, sowing around October, and transplanting in the open field can significantly delay bolting, while a sowing date in late August should be selected for seed production, and the seedlings should be transplanted in a plastic tunnel to accelerate development of the flower buds.