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Completion of the whole genome sequencing of citrus enabled us to perform genome-wide identification and functional analysis of the gene families involved in agronomic traits and morphological diversity of citrus. In this study, 22 CitARF, 11 CitGH3 and 26 CitAUX/IAA genes were identified in citrus, respectively. Phylogenetic analysis revealed that all the genes of each gene family could be subdivided into three groups and showed strong evolutionary conservation. The GH3 and AUX/IAA gene families shrank and ARF gene family was highly conserved in the citrus genome after speciation from Arabidopsis thaliana. Tissue-specific expression profiles revealed that 54 genes were expressed in at least one tissue while just 5 genes including CitARF07, CitARF20, CitGH3.04, CitAUX/IAA25 and CitAUX/IAA26 with very low expression level in all tissues tested, suggesting that the CitARF, CitGH3 and CitAUX/IAA gene families played important roles in the development of citrus organs. In addition, our data found that the expression of 2 CitARF, 4 CitGH3 and 4 AUX/IAA genes was affected by IAA treatment, and 7 genes including, CitGH3.04, CitGH3.07, CitAUX/IAA03, CitAUX/IAA04, CitAUX/IAA18, CitAUX/IAA19 and CitAUX/IAA23 were related to fruitlet abscission. This study provides a foundation for future studies on elucidating the precise role of citrus ARF, GH3 and AUX/IAA genes in early steps of auxin signal transduction and open up a new opportunity to uncover the molecular mechanism underlying citrus fruitlet abscission.

Citrus, as one of the most economically important fruits worldwide, is adversely affected by salinity stress. However, its molecular mechanisms underlying salinity tolerance are still not clear. In this study, next-generation RNA-seq technology was applied to analyze the gene expression profiling of citrus roots at 3 time points over a 24-h period of salt treatment. A total of 1831 differentially expressed genes (DEGs) were identified. Among them, 1195 and 1090 DEGs were found at 4 and 24 h, of which 454 were overlapped. Based on functional annotation, the salt overly sensitive (SOS) and reactive oxygen species (ROS) signaling pathways were found to be involved. Meanwhile, we found that hormone metabolism and signaling played important roles in salt stress. In addition, a multitude of transcription factors (TFs) including WRKY, NAC, MYB, AP2/ERF, bZIP, GATA, bHLH, ZFP, SPL, CBF, and CAMTA were identified. The genes related to cell wall loosening and stiffening (xyloglucan endotransglucosylase/hydrolases, peroxidases) were also involved in salt stress. Our data not only provided a genetic resource for discovering salt tolerance-related genes, but also furthered our understanding of the molecular mechanisms underlying salt tolerance in citrus.

It is widely accepted that fruit abscission is a highly regulated developmental process that is both influenced and activated in response to changing environment and plays crucial roles in the health and reproductive success of plants. Recent evidences showed that numerous genes related to metabolic and signalling pathways were coordinately implicated in regulating fruit abscission. Cross talks within hormones, between saccharides and hormones, as well as between polyamines and ethylene result in synergetic or antagonistic interactions which together play an important role in adjusting fruit abscission. Although hormones are the most studied internal factors related to abscission, the role of saccharides and polyamines during fruit abscission is emerging now. The characterizations of the molecular mechanisms of regulating fruit abscission are essential to develop effective strategies for controlling this process in plants.

The remarkable lubrication properties of normal articular cartilage play an essential role in daily life, providing almost frictionless movements of joints. Alterations of cartilage surface or degradation of biomacromolecules within synovial fluid increase the wear and tear of the cartilage and hence determining the onset of the most common joint disease, osteoarthritis (OA). The irreversible and progressive degradation of articular cartilage is the hallmark of OA. Considering the absence of effective options to treat OA, the mechanosensitivity of chondrocytes has captured attention. As the only embedded cells in cartilage, the metabolism of chondrocytes is essential in maintaining homeostasis of cartilage, which triggers motivations to understand what is behind the low friction of cartilage and develop biolubrication-based strategies to postpone or even possibly heal OA. This review firstly focuses on the mechanism of cartilage lubrication, particularly on boundary lubrication. Then the mechanotransduction (especially shear stress) of chondrocytes is discussed. The following summarizes the recent development of cartilage-inspired biolubricants to highlight the correlation between cartilage lubrication and OA. One might expect that the restoration of cartilage lubrication at the early stage of OA could potentially promote the regeneration of cartilage and reverse its pathology to cure OA.

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