SummaryCucumber fruit spine is multicellular and non-branched with no endoreduplication. Spines in the tbh mutant were tiny and branched. Meristem regulators and polarity genes regulate spine development in cucumber.

Cuticular waxes play an important part in protecting plant aerial organs from biotic and abiotic stresses. In previous studies, the biosynthetic pathway of cuticular waxes and relative functional genes has been researched and understood; however, little is known in cucumber (Cucumis sativus L.). In this study, we cloned and characterized an AtWAX2 homolog, CsWAX2, in cucumber and found that it is highly expressed in the epidermis, where waxes are synthesized, while subcellular localization showed that CsWAX2 protein is localized to the endoplasmic reticulum (ER). The transcriptional expression of CsWAX2 was found to be induced by low temperature, drought, salt stress and ABA, while the ectopic expression of CsWAX2 in an Arabidopsis wax2 mutant could partially complement the glossy stem phenotype. Abnormal expression of CsWAX2 in transgenic cucumbers specifically affected both very long chain (VLC) alkanes and cutin biosynthesis. Furthermore, transgenic cucumber plants of CsWAX2 showed significant changes in pollen viability and fruit resistance to water loss and pathogens compared with the wild type. Collectively, these results indicated that CsWAX2 plays a pivotal role in wax biosynthesis, influencing pollen fertility and the plant's response to biotic and abiotic stresses.

Most land plants have a wax layer which covers their aerial parts to protect them from environmental stresses, such as drought, UV radiation, and pathogenic invasion. The wax biosynthesis has been well studied previously in Arabidopsis, but it still remains elusive in cucumber. Here, we isolated a CER1 homolog CsCER1 in cucumber, and we found that the expression of CsCER1 in the cucumber line 3401 which shows waxy fruit phenotype is much higher than that in the cucumber line 3413 which displays glossy fruit phenotype. Spatial and temporal expression analyses revealed that CsCER1 is specifically expressed in the epidermis where waxes are synthesized, and sub-cellular location showed that CsCER1 protein is localized to the endoplasmic reticulum. The expression of CsCER1 can be induced by low temperature, drought, salt stress and abscisic acid. In addition, abnormal expressions of CsCER1 in transgenic cucumber plants have dramatic effects on very-long-chain (VLC) alkanes biosynthesis, cuticle permeability, and drought resistance. Our data suggested that CsCER1 plays an important role in VLC alkanes biosynthesis in cucumber.

SummaryWe find that CsGAMYB1, a positive regulator of GA signalling, can regulate sex expression of cucumber. This provides a new insight into the mechanism of GA in sex determination.

Shoot organ primordia are initiated from the shoot apical meristem and develop into leaves during the vegetative stage, and into flowers during the reproductive phase. Between the meristem and the newly formed organ primordia, a boundary with specialized cells is formed that separates meristematic activity from determinate organ growth. Despite interactions that have been found between boundary regulators with genes controlling meristem maintenance or primordial development, most boundary studies were performed during embryogenesis or vegetative growth, hence little is known about whether and how boundaries communicate with meristem and organ primordia during the reproductive stage. We combined genetic, molecular and biochemical tools to explore interactions between the boundary gene HANABA TARANU (HAN) and two meristem regulators BREVIPEDICELLUS (BP) and PINHEAD (PNH), and three primordia-specific genes PETAL LOSS (PTL), JAGGED (JAG) and BLADE-ON-PETIOLE (BOP) during flower development. We demonstrated the key role of HAN in determining petal number, as part of a set of complex genetic interactions. HAN and PNH transcriptionally promote each other, and biochemically interact to regulate meristem organization. HAN physically interacts with JAG, and directly stimulates the expression of JAG and BOP2 to regulate floral organ development. Further, HAN directly binds to the promoter and intron of CYTOKININ OXIDASE 3 (CKX3) to modulate cytokinin homeostasis in the boundary. Our data suggest that boundary-expressing HAN communicates with the meristem through the PNH, regulates floral organ development via JAG and BOP2, and maintains boundary morphology through CKX3 during flower development in Arabidopsis.