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Background: TLPs (Tubby-like proteins) are widespread in eukaryotes and highly conserved in plants and animals. TLP is involved in many biological processes, such as growth, development, biotic and abiotic stress responses, while the underlying molecular mechanism remains largely unknown. In this paper we characterized the biological function of cucumber (Cucumis sativus L.) Tubby-like protein 8 (CsTLP8) in Arabidopsis. Results: In cucumber, the expression of the tubby-like protein CsTLP8 was induced by NaCl treatment, but reduced by PEG (Polyethylene Glycol) and ABA (Abscisic Acid) treatment. Subcellular localization and transcriptional activation activity analysis revealed that CsTLP8 possessed two characteristics of classical transcription factors: nuclear localization and trans-activation activity. Yeast two-hybrid assay revealed interactions of CsTLP8 with CsSKP1a and CsSKP1c, suggesting that CsTLP8 might function as a subunit of E3 ubiquitin ligase. The growth activity of yeast with ectopically expressed CsTLP8 was lower than the control under NaCl and mannitol treatments. Under osmotic and salt stresses, overexpression of CsTLP8 inhibited seed germination and the growth of Arabidopsis seedlings, increased the content of MDA (Malondialdehyde), and decreased the activities of SOD (Superoxide Dismutase), POD (Peroxidase) and CAT (Catalase) in Arabidopsis seedlings. Overexpression of CsTLP8 also increased the sensitivity to ABA during seed germination and ABA-mediated stomatal closure. Conclusion: Under osmotic stress, CsTLP8 might inhibit seed germination and seedling growth by affecting antioxidant enzymes activities. CsTLP8 acts as a negative regulator in osmotic stress and its effects may be related to ABA. [ABSTRACT FROM AUTHOR]

Originating in the subtropics, cucumbers require warm weather and plenty of light, low light inhibits the growth of cucumbers. For cucumbers to efficiently absorb light energy in low light, chlorophyll synthesis is necessary. Oxygenase for chlorophyllate is encoded by CsCAO. RNA interference (RNAi) was used to reduce CsCAO expression in cucumber, reduced chlorophyll b content and Fv/Fm (maximal photochemical efficiency of photosystem II) were found in RNAi- CsCAO lines. The Arabidopsis Atcao mutant lacks chlorophyll b and has a low Fv/Fm, but overexpressing CsCAO restored the mutant's phenotype. CsCAO gene expression was found to be upregulated in the presence of low light. The Y1H screening assay revealed that CsHsfA6b and CsBLH4 were potential CsCAO expression regulators. The results of the Y1H, LUC/REN, and EMSA assays confirmed that only CsBLH4 can bind to the CsCAO promoter. Furthermore, like Atcao , the Atblh4 mutant had low chlorophyll b content and Fv/Fm. CsCAO overexpression in the Atblh4 mutant increased the content of chlorophyll b and Fv/Fm, especially under low light conditions. CsBLH4 targeting CsCAO was found to positively regulate chlorophyll b synthesis and photosynthetic capacity in cucumber under low light conditions in our study. • Low light promoted the accumulation of chlorophyll b by up-regulating the transcription level of CsCAO. • It clarified the regulatory mechanism of BLH family member involved in chlorophyll b synthesis. • The synthesis of chlorophyll plays an important role in the response of cucumber to low light stress. [ABSTRACT FROM AUTHOR]