Genetic Variability in Seed Longevity and Germination Traits in a Tomato MAGIC Population in Contrasting Environments

Phenotypic Plasticity and Stability in Plants: Genetic Mechanisms, Environmental Adaptation, Evolutionary Implications, and Future Directions

The phenotypic display, survival, and reproduction of organisms depend on genotype-environment interactions that drive development, evolution, and diversity. Biological systems exhibit two basic but paradoxical features that contribute to developmental robustness: plasticity and stability. However, the understanding of these concepts remains ambiguous. The morphology and structure of plant reproductive organs-flowers and fruits-exhibit substantial stability but display a certain level of plasticity under environmental changes, thus representing promising systems for the study of how stability and plasticity jointly govern plant development and evolution. Beyond the genes underlying organ formation, certain genes may maintain stability and induce plasticity. Variations in relevant genes can induce developmental repatterning, thereby altering stability or plasticity under light and temperature fluctuations, which often affects fitness. The regulation of developmental robustness in plant vegetative organs involves transcriptional and post-transcriptional regulation, epigenetics, and phase separation; however, these mechanisms in the reproductive organs of flowering plants remain poorly investigated. Moreover, genes that specifically determine phenotypic plasticity have rarely been cloned. This review clarifies the concepts and attributes of phenotypic plasticity and stability and further proposes potential avenues and a paradigm to investigate the underlying genes and elucidate how plants adapt and thrive in diverse environments, which is crucial for the design of genetically modified crops.

New QTLs involved in the control of stigma position in tomato

BACKGROUND

Tomato mating systems were strongly affected by domestication events. Mutations disrupting self-incompatibility paralleled by changes retracting the stigma position (SP) within the staminal cone conferred strict autogamy and self-fertility to the cultivated forms. Although major genes affecting these changes have been identified, SP control in domesticated forms that retain a constitutive or heat-inducible noninserted SP needs elucidation. To widen the possibility of identifying SP genetic determinants, we analyzed the trait in four populations (two germplasm collections, a multiparental recombinant inbred and a biparental progeny) under different environmental conditions (normal and heat stressed).

RESULTS

Overall, 37 markers significantly associated with the trait were identified. Several colocalizations were found, both among regions first reported in this work and among them and previously reported positions. This finding supported the reliability of the analysis. Three such regions, in the long arms of chromosomes 1, 8 and 11, were validated in an independent segregating population, and candidate genes in confidence intervals were identified among transcription factors and hormone-, stress- and cell wall-related genes.

CONCLUSION

Overall, this work supported the hypothesis that the SP phenotype is controlled by different key genes in tomato, paving the way for the identification of novel players and novel mechanisms involved in the regulation of herkogamy.

Screening of NIAS World Rice Core Collection for Seeds with Long Longevity as Useful Potential Breeding Materials Focusing on the Stability of Embryonic RNAs

Seed longevity is a crucial trait for the seed industry and genetic resource preservation. To develop excellent cultivars with extended seed lifespans, it is important to understand the mechanism of keeping seed germinability long term and to find useful genetic resources as prospective breeding materials. This study was conducted to identify the best cultivars with a high and stable seed longevity trait in the germplasm of rice (Oryza sativa L.) and to analyze the correlation between seed longevity and embryonic RNA integrity. Seeds from 69 cultivars of the world rice core collection selected by the NIAS in Japan were harvested in different years and subjected to long-term storage or controlled deterioration treatment (CDT). The long-term storage (4 °C, RH under 35%, 10 years) was performed on seeds harvested in 2010 and 2013. The seeds harvested in 2016 and 2019 were used for CDT (36 °C, RH of 80%, 40 days). Seed longevity and embryonic RNA integrity were estimated by a decrease in the germination percentage and RNA integrity number (RIN) after long-term storage or CDT. The RIN value was obtained by the electrophoresis of the total RNA extracted from the seed embryos. Seeds of "Vandaran (indica)", "Tupa 729 (japonica)", and "Badari Dhan (indica)" consistently showed higher seed longevity and embryonic RNA integrity both under long-term storage and CDT conditions regardless of the harvest year. A strong correlation (R2 = 0.93) was observed between the germination percentages and RIN values of the seeds after the long-term storage or CDT among nine cultivars selected based on differences in their seed longevity. The study findings revealed the relationship between rice seed longevity and embryo RNA stability and suggested potential breeding materials including both japonica and indica cultivars for improving rice seed longevity.

A method to determine antifungal activity in seed exudates by nephelometry

BACKGROUND

One of the levers towards alternative solutions to pesticides is to improve seed defenses against pathogens, but a better understanding is needed on the type and regulation of existing pathways during germination. Dormant seeds are able to defend themselves against microorganisms during cycles of rehydration and dehydration in the soil. During imbibition, seeds leak copious amounts of exudates. Here, we developed a nephelometry method to assay antimicrobial activity (AA) in tomato seed exudates as a proxy to assess level of defenses.

RESULTS

A protocol is described to determine the level of AA against the nonhost filamentous fungus Alternaria brassicicola in the exudates of tomato seeds and seedlings. The fungal and exudate concentrations can be adjusted to modulate the assay sensitivity, thereby providing a large window of AA detection. We established that AA in dormant seeds depends on the genotype. It ranged from very strong AA to complete absence of AA, even after prolonged imbibition. AA depends also on the stages of germination and seedling emergence. Exudates from germinated seeds and seedlings showed very strong AA, while those from dormant seeds exhibited less activity for the same imbibition time. The exudate AA did not impact the growth of a pathogenic fungus host of tomato, Alternaria alternata, illustrating the adaptation of this fungus to its host.

CONCLUSIONS

We demonstrate that our nephelometry method is a simple yet powerful bioassay to quantify AA in seed exudates. Different developmental stages from dormant seed to seedlings show different levels of AA in the exudate that vary between genotypes, highlighting a genetic diversity x developmental stage interaction in defense. These findings will be important to identify molecules in the exudates conferring antifungal properties and obtain a better understanding of the regulatory and biosynthetic pathways through the lifecycle of seeds, from dormant seeds until seedling emergence.