Discovery indicates mechanism to control early germination

Researchers have uncovered a central translational regulation mechanism that controls the transition from seed to seedling. The study paves the way for genetic strategies to prevent early sprouting in cereals — a recurring problem that compromises agricultural productivity in several countries.

Germination marks the end of dormancy and the beginning of active plant growth. This phase depends on internal hormonal signals, such as the balance between abscisic acid (ABA) and gibberellins (GA), and also on external factors such as light, temperature and humidity.

When seeds germinate before harvest, while still attached to the ear, the phenomenon is called preharvest sprouting (PHS). The consequence is severe losses in grain production. To overcome this challenge, the study investigated the molecular processes that regulate germination, with an emphasis on the translation of messenger RNAs stored in the seeds.

The team used combined transcriptome and translatome analyses to map gene expression during germination. In mutants with defective ribosomes, germination was delayed. The cause was traced back to the ABA2 gene, which is essential for ABA production. They found that a regulatory sequence at the beginning of the messenger RNA — called the upstream open reading frame (uORF) — acts as a brake, inhibiting the translation of the ABA2 protein.

By genetically editing this uORF with CRISPR-Cas9 in rice, scientists were able to eliminate early sprouting. The technique removed the sequence that inhibits ABA2 production, allowing greater accumulation of the hormone that maintains seed dormancy.

Two major uORF haplotypes were identified among rice cultivars. These natural genetic variations modulate the expression of the OsABA2 gene and, as a result, influence the degree of resistance to early sprouting. This shows that translational regulation of ABA2 plays a decisive role in controlling germination and that genetic diversity can be used in breeding programs.

The work also revealed that the mechanism is conserved in Arabidopsis thaliana, a model plant in plant biology. Mutants with translation deficiency or treated with translation inhibitors also showed delayed germination. The data reinforce the importance of the stored RNA translation machinery in the first hours of germination.

In addition to identifying a critical link between dormancy and gene translation, the results provide a practical strategy: genetically modifying the uORF to control germination. The study also proposes the selection of favorable haplotypes in current cultivars as a non-transgenic alternative.

More information at doi.org/10.1073/pnas.2502155122