Tuberculate fruit gene Tu encodes a C₂H₂ zinc finger protein that is required for the warty fruit phenotype in cucumber (Cucumis sativus L.)

Abstract

SUMMARYCucumber fruits that have tubercules and spines (trichomes) are known to possess a warty (Wty) phenotype. In this study, the tuberculate fruit gene Tu was identified by map-based cloning, and was found to encode a transcription factor (TF) with a single C 2 H 2 zinc finger domain. Tu was identified in all 38 Wty lines examined, and was completely absent from all 56 non-warty (nWty) lines. Cucumber plants transgenic for Tu (TCP) revealed that Tu was required for the Wty fruit phenotype. Subcellular localization showed that the fusion protein GFP-Tu was localized mainly to the nucleus. Based on analyses of semi-quantitative and quantitative reverse transcription polymerase chain reaction (RT-PCR), and mRNA in situ hybridization, we found that Tu was expressed specifically in fruit spine cells during development of fruit tubercules. Moreover, cytokinin (CTK) content measurements and cytological observations in Wty and nWty fruits revealed that the Wty fruit phenotype correlated with high endogenous CTK concentrations. As a result of further analyses on the transcriptomic profile of the nWty fruit epidermis and TCP fruit warts, expression of CTKassociated genes, and hormone content in nWty fruit epidermis, Wty fruit warts and epidermis, and TCP fruit warts and epidermis, we found that Tu probably promoted CTK biosynthesis in fruit warts. Here we show that Tu could not be expressed in the glabrous and tubercule-free mutant line gl that contained Tu, this result that futher confirmed the epistatic effect of the trichome (spine) gene Gl over Tu. Taken together, these data led us to propose a genetic pathway for the Wty fruit trait that could guide future mechanistic studies.

A Sequencing-Based Linkage Map of Cucumber

“…The major-effect QTL for fruit wart size, fws5, was resolved into a single bin C5B506 in all four trials ( Figure 1D); it was 520 kb in length and harbored the cloned fruit wart gene Tu (Yang et al, 2014). The major QTL for uniform immature fruit color u5 was also mapped to the bin C5B506 in all three trials ( Figure 1D); it contained the 313.2-kb interval previously determined using 800 segregants (Yang et al, 2013).…”

Genome-Wide Mapping of Structural Variations Reveals a Copy Number Variant That Determines Reproductive Morphology in Cucumber

“…Seven signals were significantly associated with the trait (P < 1e 28 ) (Supplemental Figure 6), including one that resided within the genetically mapped tu region on chromosome 5, which has previously been reported to determine the formation of fruit tubercules (Zhang et al, 2010a). This SV involves the deletion of the entire tu gene (Csa5G577350, encoding a C 2 H 2 type zinc finger transcription factor) (Yang et al, 2014) in five Eurasian cucumber lines (Supplemental Figure 6). In addition, our analysis indicated that this deletion is caused by a microhomolog (AATT) at the breakpoints (Supplemental Figure 6), elucidating the formation of tu, a null allele explored by breeders for developing cultivars for European and US supermarkets where cucumbers are generally packed in plastic for transportation and longer shelf-life (and thus must be spineless).…”

Next generation sequencing and omics in cucumber ( Cucumis sativus L.) breeding directed research

“…Warty phenotype occurs when trichromes are combined with tubercules. The nWty fuits against Wty, are smoother, better in taste and possess lower pesticide residues, they are easy to wash, transport and store [16,33]. The map-based cloning study of nWty and Wt cucumber lines revealed presence of Tu (tuberculate) gene in all warty fruits, which seems that this gene is needed for warty fruits phenotype formation.…”