Genetic regulation of shoot architecture in cucumber

Abstract

Cucumber (Cucumis sativus L.) is an important vegetable crop species with great economic value. Shoot architecture determines the visual appearance of plants and has a strong impact on crop management and yield. Unlike most model plant species, cucumber undergoes vegetative growth and reproductive growth simultaneously, in which leaves are produced from the shoot apical meristem and flowers are generated from leaf axils, during the majority of its life, a feature representative of the Cucurbitaceae family. Despite substantial advances achieved in understanding the regulation of plant form in Arabidopsis thaliana, rice, and maize, our understanding of the mechanisms controlling shoot architecture in Cucurbitaceae crop species is still limited. In this review, we focus on recent progress on elucidating the genetic regulatory pathways underlying the determinant/indeterminant growth habit, leaf shape, branch outgrowth, tendril identity, and vine length determination in cucumber. We also discuss the potential of applying biotechnology tools and resources for the generation of ideal plant types with desired architectural features to improve cucumber productivity and cultivation efficiency.

Fig. 1. Shoot architecture of cucumber, maize, tomato, Arabidopsis, and rice.

Representations of shoot architecture of cultivated: A cucumber, B maize, C tomato, D wild cucumber, E Arabidopsis thaliana, and F rice. ins, indeterminate shoot tip; ffb, female flower bud; ten, tendril; mfb, male flower bud; fr, fruit; ci, compound inflorescence; syfr, sympodial fruit

Fig. 2. CsLFY and CsTFL1 coregulate the indeterminate/determinate growth habit of cucumber.

Cucumber plants with: A indeterminate, and C determinate growth habits. B CsTFL1 promotes indeterminate growth by forming a complex together with CsNOT2a and CsFDP to repress floral meristem development. CsLFY directly interacts with CsWUS in the SAM to maintain stem cell identity and thus maintain an indeterminate growth habit. D The absence of CsTFL1 or CsLFY results in a determinate growth habit of cucumber

Fig. 3. Morphological phenotypes of representative cucumber leaf mutants or transgenic lines.

A Typical leaf of cucumber, B the round leaf (rl) mutant, C the mango fruit (mf) mutant, D the CsIVP-RNAi line, E the CsYAB5-RNAi line, F the curly leaf-1 (cl-1) and curly leaf-2 (cl-2) mutants, G the little leaf (ll) mutant and its WT control, and H the CsHAN1-RNAi line. The causal genes underlying the phenotype are listed

Fig. 4. CsBRC1 represses bud outgrowth by directly inhibiting CsPIN3 activity in cucumber.

A Representative cucumber plant with no branch outgrowth. B CsBRC1 negatively regulates bud outgrowth by directly inhibiting the transcription of the auxin transporter CsPIN3 and thus auxin accumulation in lateral buds. C Representative cucumber plant with many lateral branches. D The absence of CsBRC1 leads to increased expression of CsPIN3, depleted auxin accumulation in the buds, and lateral bud outgrowth of cucumber. lb: lateral branch