NS encodes an auxin transporter that regulates the ‘numerous spines’ trait in cucumber (Cucumis sativus) fruit

Abstract

SUMMARY Fruit spine is an important agronomic trait in cucumber and the “numerous spines (ns)” cucumber varieties are popular in Europe and West Asia. Although the classical genetic locus of ns was reported more than two decades ago, the NS gene has not been cloned yet. In this study, nine genetic loci for the different densities of fruit spines were identified by a genome‐wide association study. Among the nine loci, fsdG2.1 was closely associated with the classical genetic locus ns, which harbors a candidate gene Csa2G264590. Overexpression of Csa2G264590 resulted in lower fruit spine density, and the knockout mutant generated by CRISPR/Cas9 displayed an increased spine density, demonstrating that the Csa2G264590 gene is NS. NS is specifically expressed in the fruit peel and spine. Genetic analysis showed that NS regulates fruit spine development independently of the tuberculate gene, Tu, which regulates spine development on tubercules; the cucumber glabrous mutants csgl1 and csgl3 are epistatic to ns. Furthermore, we found that auxin levels in the fruit peel and spine were significantly lower in the knockout mutant ns‐cr. Moreover, RNA‐sequencing showed that the plant hormone signal transduction pathway was enriched. Notably, most of the auxin responsive Aux/IAA family genes were downregulated in ns‐cr. Haplotype analysis showed that the non‐functional haplotype of NS exists exclusively in the Eurasian cucumber backgrounds. Taken together, the cloning of NS gene provides new insights into the regulatory network of fruit spine development.

Morphological and Genetic Diversity of Cucumber (Cucumis sativus L.) Fruit Development

“…Cucumber fruit are often marked by the presence of warts comprised of tubercules (raised fruit surface) topped with spines ( Figure 2 ). The spines are large, multicellular, non-branched, non-glandular trichomes (type II in tomato trichome nomenclature), composed of an enlarged base and pointed stalk [ 82 ]. Although spines are most frequently located on tubercules, the two traits can be disassociated, i.e., spines can be present without tubercules [ 83 ].…”

Quite the pickle: an auxin influx carrier controls spine formation in cucumber

“…This indicates that the numerous spines phenotype is caused by a loss of function of this candidate gene. In this issue of The Plant Journal, Zhang and his colleagues investigated how the gene is involved in spine formation (Liu et al., 2022).…”

“…To investigate whether a loss‐of‐function at NS is indeed involved in the numerous spines phenotype, Liu et al. (2022) constructed overexpression and knockout lines. The overexpression lines developed fruits with fewer spines, whereas the knockout mutant had fruits with more spines (Figure1).…”

“…Because NS was predicted to encode an auxin transport protein, Liu et al. (2022) tested whether NS affects fruit spine density by regulating auxin levels. The fruit peel of the knockout mutant accumulated less auxin and contained 2 × less auxin indole‐3‐acetic acid than the peels of wild‐type cucumber.…”

“…The cucumber genome has seven AUX1/LAX genes. To test whether other family members are also involved in spine density, Liu et al (2022) used in situ hybridization to investigate their expression patterns. However, these other AUX1/LAX genes were expressed in other tissues, such as roots, stems, tendrils and male flowers.…”