Dissecting stylar responses to self-pollination in wild tomato self-compatible and self-incompatible species using comparative proteomics

Proteomics of Reproductive Development, Fruit Ripening, and Stress Responses in Tomato

The fruits of the tomato crop (Solanum lycopersicum L.) are increasingly consumed by humans worldwide. Due to their rich nutritional quality, pharmaceutical properties, and flavor, tomato crops have gained a salient role as standout crops among other plants. Traditional breeding and applied functional research have made progress in varying tomato germplasms to subdue biotic and abiotic stresses. Proteomic investigations within a span of few decades have assisted in consolidating the functional genomics and transcriptomic research. However, due to the volatility and dynamicity of proteins in the regulation of various biosynthetic pathways, there is a need for continuing research in the field of proteomics to establish a network that could enable a more comprehensive understanding of tomato growth and development. With this view, we provide a comprehensive review of proteomic studies conducted on the tomato plant in past years, which will be useful for future breeders and researchers working to improve the tomato crop.

Self- and Cross-Pollination in Argane Tree and their Implications on Breeding Programs

The argane tree (Argania spinosa L.) is a mostly self-incompatible species that must be cross-pollination. However, the cross-pollination is often insufficient to obtain a desirable fruit yield in the absence of compatibility between the orchard’s argane trees. Proper pollination design is therefore essential to ensure a supply of compatible pollen. In this study, pollen germination and pollen development following cross- and self-pollination were investigated in A. spinosa. The choice of compatible parents or a pollinizer is currently a new research topic for the production of argane fruits in the framework of argane farming programs. Different pollination experiments were designed with two main objectives: (i) to study cross/self-(in)compatibility in the argane tree, and (ii) to determine the degree of compatibility between selected superior genotypes for pollination strategies to improve fruit set in argane orchards. Thus, to determine if a pollination deficit exists, experiments were carried out on 14 genotypes, and 5421 flowers served as sampling. The germination rate of pollen was lower than 50% for three genotypes, and only four genotypes bloom twice a year. From cross-pollination trials, traits related to the mother trees, such as the shape of the fruit and fruit ripening duration, are not influenced by the gene flow transmitted by pollens. Self-pollination was very low (0.2%) for both hand- and free self-pollination but the highest fruit set rate observed was 5.3%. Based on the pollen effect study results, it can be concluded that different pollen sources affected the fruit set. Thus, the choice of an efficient pollinizer genotype must be inter-compatible with the main variety, bloom at the same time, and be regular (no alternation). This is the first time that a pollinizer tree was reported and studied for argane. To meet future argane farming requirements, the number and location of compatible pollinizers is very important in the argane orchard design. This design of pollination remains to be checked by alternately planting a row of pollinizer trees or inter-rows with main varieties.

Study on the molecular mechanism of Laccaria bicolor helping Populus trichocarpa to resist the infection of Botryosphaeria dothidea

AIMS

This study explored the specific molecular mechanism of Laccaria bicolor to help Populus trichocarpa resist infection by Botryosphaeria dothidea.

METHODS AND RESULTS

Transcriptome technology was used to sequence P. trichocarpa under disease stress, and a total of 6379 differentially expressed genes (DEGs) were identified. A total of 536 new DEGs were induced by L. bicolor during the infection of B. dothidea. L. bicolor helps to prevent and alleviate the infection of B. dothidea by regulating related genes in the cell wall pathway, signal transduction pathway, disease-resistant protein synthesis pathway and antioxidant enzyme synthesis pathway of P. trichocarpa.

CONCLUSION

The inoculation of L. bicolor can regulate the expression of genes in the cell wall pathway and enhance the physical defense capabilities of plants. Under disease stress conditions, L. bicolor can regulate signal transduction pathways, disease-resistant related pathways and reactive oxygen species (ROS) clearance pathways to help P. trichocarpa alleviate the disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

The research reveals the mechanism of L. bicolor inducing resistance to canker of P. trichocarpa from the molecular level and provides a theoretical basis for the practical application of mycorrhizal fungi to improve plant disease resistance.

Using RNA-seq to characterize pollen-stigma interactions for pollination studies

Insects are essential for the reproduction of pollinator-dependent crops and contribute to the pollination of 87% of wild plants and 75% of the world’s food crops. Understanding pollen flow dynamics between plants and pollinators is thus essential to manage and conserve wild plants and ensure yields are maximized in food crops. However, the determination of pollen transfer in the field is complex and laborious. We developed a field experiment in a pollinator-dependent crop and used high throughput RNA sequencing (RNA-seq) to quantify pollen flow by measuring changes in gene expression between pollination treatments across different apple (Malus domestica Borkh.) cultivars. We tested three potential molecular indicators of successful pollination and validated these results with field data by observing single and multiple visits by honey bees (Apis mellifera) to apple flowers and measured fruit set in a commercial apple orchard. The first indicator of successful outcrossing was revealed via differential gene expression in the cross-pollination treatments after 6 h. The second indicator of successful outcrossing was revealed by the expression of specific genes related to pollen tube formation and defense response at three different time intervals in the stigma and the style following cross-pollination (i.e. after 6, 24, and 48 h). Finally, genotyping variants specific to donor pollen could be detected in cross-pollination treatments, providing a third indicator of successful outcrossing. Field data indicated that one or five flower visits by honey bees were insufficient and at least 10 honey bee flower visits were required to achieve a 25% probability of fruit set under orchard conditions. By combining the genotyping data, the differential expression analysis, and the traditional fruit set field experiments, it was possible to evaluate the pollination effectiveness of honey bee visits under orchards conditions. This is the first time that pollen-stigma-style mRNA expression analysis has been conducted after a pollinator visit (honey bee) to a plant (in vivo apple flowers). This study provides evidence that mRNA sequencing can be used to address complex questions related to stigma–pollen interactions over time in pollination ecology.