The Arabidopsis Group 1 LATE EMBRYOGENESIS ABUNDANT Protein ATEM6 Is Required for Normal Seed Development

Abstract

As part of the embryo maturation process, orthodox seeds undergo a developmentally regulated dehydration period. The LATE EMBRYOGENESIS ABUNDANT (LEA) genes encode a large and diverse family of proteins expressed during this time. Many hypothesize that LEA proteins act by mitigating water loss and maintaining cellular stability within the desiccated seed, although the mechanisms of their actions remain largely unknown. The model plant Arabidopsis (Arabidopsis thaliana) contains two genes belonging to the group 1 LEA family, ATEM1 and ATEM6, and knockout mutations in these genes are being sought as a means to better understand group 1 LEA protein function during embryo maturation. We have identified a T-DNA insertion allele of the ATEM6 gene in which the T-DNA is present just downstream of the protein coding region. While this gene is transcriptionally active and encodes a wild-type protein, there is no detectable ATEM6 protein in mature seeds. Mutant seeds display premature seed dehydration and maturation at the distal end of siliques, demonstrating that this protein is required for normal seed development. We propose that one function for group 1 LEA proteins in seed development is to buffer the water loss that occurs during embryo maturation and that loss of ATEM6 expression results in the mutant phenotype.

Hydrophilic protein associated with desiccation tolerance exhibits broad protein stabilization function

“…For example, group 1 proteins are highly seed-specific and might act as hydration buffers to slow dehydration rates during seed development (30). However, because group 3 LEA proteins are common to both plants and animals, it is likely they confer a function essential for desiccation tolerance across a wide phylogenetic spectrum.…”

The Enigmatic LEA Proteins and Other Hydrophilins

“…Tolerance to stress conditions induced by the constitutive expression of genes from this group has not been reported in plants; however, the expression of wheat TaEm in S. cerevisiae seems to attenuate the growth inhibition of yeast cultures normally observed in high-osmolarity media (Swire-Clark and Marcotte, 1999). Also, the absence of one of two group 1 members in Arabidopsis plants led to a subtle phenotype of premature seed dehydration and maturation, suggesting a role during seed development (Manfre et al, 2006). The expression in vegetative tissues from plants grown under optimal growth conditions of some of the group 1 LEA proteins implies that they may also have a role during normal seed/seedling development.…”

LEA Proteins During Water Stress: Not Just for Plants Anymore

“…There are no direct measurements of changes in the kinetics of cellular water loss attributable to the presence of LEA proteins to our knowledge. Across days of development within the seed capsule of intact Arabidopsis thaliana, mutant seeds deficient in expression of ATEM6 (group 1 LEA protein) reached a dehydrated state earlier than wild-type seeds based on morphological evidence (94). However, additional developmental characteristics also appeared to be accelerated in the mutant, so conclusions about absolute differences in water loss rate between mutant and control seeds could benefit from measurement of water kinetics in isolated seeds.…”