Functional analyses of lipocalin proteins in tomato

Organophosphate esters uptake, translocation and accumulation in rice (Oryza sativa L.): impacts of lipid transporters and chemical properties

To explore key factors involved in the uptake, translocation and accumulation of organophosphate esters (OPEs), computer simulation analysis and hydroponic experiments were executed. Lipid transporters with stocky-like active (SAC) cavities usually showed stronger binding affinities with the OPEs, especially when the SAC cavities belong to the Fish Trap model according to molecular docking. In our hydroponic trial, the binding affinity and gene expression of the lipid transporters and log Kow of the OPEs could be charged to the uptake, translocation and accumulation of the OPEs; however, these three factors played various important roles in roots and shoots. In detail, the effect of gene expression and binding affinity were stronger than log Kow in roots uptake and accumulation, but the result was the opposite in the shoots translocation. Transporters OsTIL and OsLTPL1 among all investigated transporters could play key roles in transporter-mediated OPE uptake, translocation and accumulation in the roots and shoots. OsMLP could be involved in the bidirected vertical translocation of the OPEs. OsLTP2 and OsLTP4 mainly acted as transporters of the OPEs in roots.

The OsTIL1 lipocalin protects cell membranes from reactive oxygen species damage and maintains the 18:3-containing glycerolipid biosynthesis under cold stress in rice

Lipocalins constitute a conserved protein family that binds to and transports a variety of lipids while fatty acid desaturases (FADs) are required for maintaining the cell membrane fluidity under cold stress. Nevertheless, it remains unclear whether plant lipocalins promote FADs for the cell membrane integrity under cold stress. Here, we identified the role of OsTIL1 lipocalin in FADs-mediated glycerolipid remodeling under cold stress. Overexpression and CRISPR/Cas9 mediated gene edition experiments demonstrated that OsTIL1 positively regulated cold stress tolerance by protecting the cell membrane integrity from reactive oxygen species damage and enhancing the activities of peroxidase and ascorbate peroxidase, which was confirmed by combined cold stress with a membrane rigidifier dimethyl sulfoxide or a H2 O2 scavenger dimethyl thiourea. OsTIL1 overexpression induced higher 18:3 content, and higher 18:3/18:2 and (18:2 + 18:3)/18:1 ratios than the wild type under cold stress whereas the gene edition mutant showed the opposite. Furthermore, the lipidomic analysis showed that OsTIL1 overexpression led to higher contents of 18:3-mediated glycerolipids, including galactolipids (monoglactosyldiacylglycerol and digalactosyldiacylglycerol) and phospholipids (phosphatidyl glycerol, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine and phosphatidyl inositol) under cold stress. RNA-seq and enzyme linked immunosorbent assay analyses indicated that OsTIL1 overexpression enhanced the transcription and enzyme abundance of four ω-3 FADs (OsFAD3-1/3-2, 7, and 8) under cold stress. These results reveal an important role of OsTIL1 in maintaining the cell membrane integrity from oxidative damage under cold stress, providing a good candidate gene for improving cold tolerance in rice.

Genome-wide identification and comparative analysis of lipocalin families in Lepidoptera with an emphasis on Bombyx mori

Lipocalins exhibit functional diversity, including roles in retinol transport, invertebrate cryptic coloration, and stress response. However, genome-wide identification and characterization of lipocalin in the insect lineage have not been thoroughly explored. Here, we found that a lineage-specific expansion of the lipocalin genes in Lepidoptera occurred in large part due to tandem duplication events and several lipocalin genes involving insect coloration were expanded more via tandem duplication in butterflies. A comparative analysis of conserved motifs showed both conservation and divergence of lepidopteran lipocalin family protein structures during evolution. We observe dynamic changes in tissue expression preference of paralogs in Bombyx mori, suggesting differential contribution of paralogs to specific organ functions during evolution. Subcellular localization experiments revealed that lipocalins localize to the cytoplasm, nuclear membrane, or nucleus in BmN cells. Moreover, several lipocalin genes exhibited divergent responses to abiotic and biotic stresses, and 1 lipocalin gene was upregulated by 300 fold in B. mori. These results suggest that lipocalins act as signaling components in defense responses by mediating crosstalk between abiotic and biotic stress responses. This study deepens our understanding of the comprehensive characteristics of lipocalins in insects.

The Fruit Proteome Response to the Ripening Stages in Three Tomato Genotypes

The tomato is a horticultural crop that appears in various colors as it ripens. Differences in the proteome expression abundance of a tomato depend on its genotype and ripening stage. Thus, this study aimed to confirm the differences in changes in the proteome according to four ripening stages (green, breaker, turning, and mature) of three tomato genotypes, i.e., yellow, black, and red tomatoes, using a gel-based proteomic technique. The number of protein spots shown as two-dimensional electrophoresis (2-DE) gels differed according to tomato genotype and ripening stage. A total of 286 variant proteins were determined using matrix-assisted laser desorption-time of flight (MALDI-TOF) mass spectrometry (MS) analysis, confirming 233 identified protein functions. In three tomato genotypes in each ripening stage, grouping according to the Munich Information Center for Protein Sequences (MIPS) functional categories confirmed the variant proteins involved in the following: energy processes (21%); metabolism (20%); protein fate (15%); protein synthesis (10%); a protein with a binding function or cofactor requirement (8%); cell rescue, defense, and virulence (8%); cellular transport, transport facilitation, and transport routes (6%); the biogenesis of cellular components (5%); cell cycle and DNA processing (2%); others (5%). Among the identified protein spots in the function category, two proteins related to metabolism, four related to energy, four related to protein synthesis, and two related to interaction with the cellular environment showed significantly different changes according to the fruit color by the ripening stage. This study reveals the physiological changes in different types of tomatoes according to their ripening stage and provides information on the proteome for further improvement.

Ectopic expression of human apolipoprotein D in Arabidopsis plants lacking chloroplastic lipocalin partially rescues sensitivity to drought and oxidative stress

The chloroplastic lipocalin (LCNP) is induced in response to various abiotic stresses including high light, dehydration and low temperature. It contributes to protection against oxidative damage promoted by adverse conditions by preventing accumulation of fatty acid hydroperoxides and lipid peroxidation. In contrast to animal lipocalins, LCNP is poorly characterized and the molecular mechanism by which it exerts protective effects during oxidative stress is largely unknown. LCNP is considered the ortholog of human apolipoprotein D (APOD), a protein whose lipid antioxidant function has been characterized. Here, we investigated whether APOD could functionally replace LCNP in Arabidopsis thaliana. We introduced APOD cDNA fused to a chloroplast transit peptide encoding sequence in an Arabidopsis LCNP KO mutant line and challenged the transgenic plants with different abiotic stresses. We demonstrated that expression of human APOD in Arabidopsis can partially compensate for the lack of the plastid lipocalin. The results are consistent with a conserved function of APOD and LCNP under stressful conditions. However, if the results obtained with the drought and oxidative stresses point to the protective effect of constitutive expression of APOD in plants lacking LCNP, this effect is not as effective as that conferred by LCNP overexpression. Moreover, when investigating APOD function in thylakoids after high light stress at low temperature, it appeared that APOD could not contribute to qH, a slowly reversible form of non-photochemical chlorophyll fluorescence quenching, as described for LCNP. This work provides a base of understanding the molecular mechanism underlying LCNP protective function.

Activation of six lipocalins genes' transcription under PCB18 stress in OsTIL-silenced Oryza sativa L

The lipocalins genes have been assigned for involving in the responses of organisms to various stress factors. The function of lipocalins under PCB18 stress was addressed by pathway complementation in the Oryza sativa L. OsTIL-silenced mutant. The growth of wild type (WT) and OsTIL-silenced mutant (MT) callus were suppressed by PCB18, and MT varieties were inhibited more seriously than WT varieties. Meanwhile, only WT varieties showed "Hormesis" effect. Compared with WT (3 day > 90.0%, 6 day ≤45.5%), MT varieties kept high removing efficiency by HPLC analysis. Varied gene transcription after OsTIL silencing was demonstrated between two varieties, especially obvious under PCB stress. Silenced OsTIL induced more protective gene transcriptions by qPCR analysis, OsVDE at 3 day, OsCHL, OsZEP1, OsZEP2 and OsUN at 6 day and OsZEP2 at 9 day. PCB18 stress further irritated these genes transcription in MT varieties. The defense stagy in WT varieties was that the transcriptions of lipocalins were inhibited to reduce PCB18 accumulation and toxicity. OsTIL could effectively limit PCB18 accumulation and toxicity. After TIL lacking, OsCHL, OsZEP1, OsZEP2 and OsUN in mutant were strongly evoked to against PCB stress. Remarkably, OsUN and OsZEP2 gene expressions were responded to PCB18 stress in both two varieties.

Function of SlTILs and SlCHL under heat and oxidative stresses in tomato

Lipocalins are very important proteins for stress resistance in plants. To better understand the function of tomato lipocalins, we observed responses to oxidative stress using over-expressed SlTIL1, SlTIL2, SlCHL, and silenced-plants. Significant differences in reactive oxygen species accumulation (oxidative damage) were observed in all tested plants under heat stress. Plants with over-expressed SlTIL1, SlTIL2, and SlCHL showed less oxidative damage compared with wild-type plants under heat stress. The expression of SlSODs was induced in over-expressed SlTIL1, SlTIL2, and SlCHL plants under normal and heat stress conditions. Furthermore, silenced PDS, SlTILs, and SlCHL plants showed slightly increasing oxidative damage under heat stress alongside with lower SlSODs under normal and stress conditions. These results suggest that SlTIL1, SlTIL2, and SlCHL were involved in antioxidant defense by eliminating ROS in tomato plants.