Different response to priming in Ceiba aesculifolia seeds is associated to the initial transcriptome landscape and to differential regulation of ABA and lipid metabolism

Abstract

The proper timing of germination is a crucial step for plant survival. In the tropical dry forest, water availability is one of the main factors affecting phenological transitions and synchronization of physiological events. The hydration-dehydration cycles that occur in this ecosystem enhance germination in the field, but the success of the treatment is affected by the quality of the seed batch. In Ceiba aesculifolia seeds, two priming-response phenotypes can arise from batch identity or time in storage, affecting the suitability of a given batch for plant recruitment from seed in restoration programs. We tracked the changes in gene expression during germination in six independent seed batches subjected to priming in order to understand the differences between priming phenotypes. The effects of priming over germination depended on the initial transcriptomic landscape of the seed batch, which in turn was affected during seed maturation or prolonged storage. The positive priming phenotype was associated to a fine-tuning of the transcriptome during germination, as well as a reduction of ABA content and the early mobilization of a fraction of the stored lipids during and after the treatment. In contrast, the seed batches with a negative priming phenotype presented a delayed imbibition-phase transition accompanied by a peak in ABA content during early imbibition, as well as an altered regulation of lipid metabolism that prevented the early mobilization of a small fraction of the storage lipids. Additionally, during the seed-seedling transition, the seeds with a negative response to priming also displayed alterations in seedling development that could compromise their survival in the field. Our data indicate that lipid mobilization, as an early indicative of the success of priming, could be an easy to implement test to assess seed batch quality aside from germination tests. Meanwhile, ABA seems to be involved in a water-status checkpoint that coordinates the decision of whether delay or progress into later stages of the germination program in C. aesculifolia. This checkpoint could be an important regulator of germination in non-dormant species from the seasonally dry tropical forest.