# Desiccation Tolerance as the Basis of Long-Term Seed Viability

## TL;DR

This paper explains how seeds can survive long periods of dryness due to specific genes and molecular mechanisms activated during maturation.

## Contribution

The paper highlights the evolution of desiccation tolerance mechanisms in plants and their regulation during seed development.

## Key findings

- Orthodox seeds can lose up to 95% of their water and remain viable due to desiccation tolerance.
- LEA proteins, sHSP, oligosaccharides, and antioxidants are key to desiccation tolerance in seeds.
- Abscisic acid and DOG1 regulate a network of transcription factors and epigenetic mechanisms for seed maturation.

## Abstract

Desiccation tolerance appeared as the key adaptation feature of photoautotrophic organisms for survival in terrestrial habitats. During the further evolution, vascular plants developed complex anatomy structures and molecular mechanisms to maintain the hydrated state of cell environment and sustain dehydration. However, the role of the genes encoding the mechanisms behind this adaptive feature of terrestrial plants changed with their evolution. Thus, in higher vascular plants it is restricted to protection of spores, seeds and pollen from dehydration, whereas the mature vegetative stages became sensitive to desiccation. During maturation, orthodox seeds lose up to 95% of water and successfully enter dormancy. This feature allows seeds maintaining their viability even under strongly fluctuating environmental conditions. The mechanisms behind the desiccation tolerance are activated at the late seed maturation stage and are associated with the accumulation of late embryogenesis abundant (LEA) proteins, small heat shock proteins (sHSP), non-reducing oligosaccharides, and antioxidants of different chemical nature. The main regulators of maturation and desiccation tolerance are abscisic acid and protein DOG1, which control the network of transcription factors, represented by LEC1, LEC2, FUS3, ABI3, ABI5, AGL67, PLATZ1, PLATZ2. This network is complemented by epigenetic regulation of gene expression via methylation of DNA, post-translational modifications of histones and chromatin remodeling. These fine regulatory mechanisms allow orthodox seeds maintaining desiccation tolerance during the whole period of germination up to the stage of radicle protrusion. This time point, in which seeds lose desiccation tolerance, is critical for the whole process of seed development.