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Rice seed development is crucial for determining both crop yield and grain quality. The embryo and endosperm—specialized structures for propagation and nutrient storage, respectively—must grow in a coordinated manner to ensure the viability of the seed.

About 30 years ago, scientists discovered an embryoless rice mutant called eml1. This mutant is valuable as a model for studying embryo-endosperm interactions and has temperature-sensitive traits that could be beneficial for breeding applications. However, the genetic mechanisms responsible for its embryoless phenotype have remained unclear.

To address this gap, a research team led by Prof. Bu Qingyun from the Northeast Institute of Geography and Agroecology of the Chinese Academy of Sciences, has identified OsBZR4 as the key regulatory gene behind embryoless rice formation and unraveled its molecular pathways. The findings were in Nature Communications on July 26.

The study confirms OsBZR4 as a master regulator of embryoless seed development. Mutations in the gene triggered embryoless seeds in 60%–100% of plants across multiple rice cultivars. Expression analysis revealed OsBZR4 is active specifically at the interface between the scutellum (a specialized embryonic structure) and endosperm, where it suppresses two genes, YUC4 and PIN5b, to control auxin levels and distribution during early seed development.

Experiments showed that exogenous auxin application or overexpression of YUC4—a gene involved in auxin synthesis—increased the frequency of embryoless seeds, while treatment with the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) reduced it.

Furthermore, this study explained the mutant's temperature sensitivity. Higher temperatures boosted embryoless seed rates in bzr4 mutants by activating OsPIL13, a gene that promotes YUC4 transcription and subsequent auxin accumulation. This cascade clarifies how temperature amplifies the embryoless trait.

Notably, introducing the bzr4 mutant allele into elite rice varieties such as ZJ10 and ZJ11 improved both milled rice yield and grain storability—key traits for agricultural productivity.

Targeted manipulation of OsBZR4 could enable the development of thermosensitive embryoless rice varieties with enhanced energy reserves and better storability, the team noted.