Mechanism of F-box protein family in plant resistance response to environmental stress

The UPS (ubiquitin proteasome system) mediated by SCF type E3 ubiquitin-ligase is an important mechanism to regulate biological progress at post-translation level. F-box protein, as a key component in SCF complex, could recognize its target protein for degradation. F-box gene family contains numerous members with vast diversity. In general, F-box protein contains F-box motif at N terminus and conserved domain of protein-protein interaction for recognizing target at C terminus. Due to vast diversity of conserved C terminus domains, F-box proteins could recognize wide varieties of targets. Also based on C terminal domains, F-box proteins could be divided into several subfamilies. It showed that plant F-box proteins were involved in many life processes, including response to environmental stress. Here, we reviewed current knowledge of plant F-box proteins in responding to stress. Most of the reported F-box proteins had been shown to function via SCF-dependent protein degradation, with few using SCF-independent mechanisms. Some well-understood F-box proteins were involved in phytohormone signaling pathways. Some reacted to stress through regulating the activity of transcription factors, which influenced expression of downstream genes responding to stress. Bioinformatics analyses of transcriptome showed that many predicted F-box genes were involved in stress-response reactions. Among these, only a few studies had dealt with the functions. The knowledge on the functions under environmental stress was summarized in this study. For drought, salinity and alkality stresses, F-box genes often regulated abscisic acid or ethylene signal pathways. Since drought and salt-alkaline stresses often occurred concomitantly, quite a few F-box genes had been identified to be involved in the response to both stresses in different ways. Some regulated the response to osmotic stress and ionic stress synergistically. However, some functioned inversely, suggesting that they played a role in fine regulations. For cold stress, F-box genes regulated CBF signal pathways. For biotic stress, F-box genes always regulated jasmonate and salicylic acid pathways. Meanwhile, pathogens attacked plant SCF complex for infection. Moreover, phytohormones had crosstalk to coordinate resistance in plants.