|Marcotte, jr., William|
Submitted to: Plant And Cell Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/27/2008
Publication Date: 12/10/2008
Citation: Manfre, A.J., Lahatte, G.A., Climer, C.R., Marcotte, Jr., W.R. 2008. Seed dehydration and the establishment of desiccation tolerance during seed maturation is altered in the Arabidopsis thaliana mutant atem6-1. Plant And Cell Physiology. 50(2):243-253. Interpretive Summary: At the end of seed development, there is a highly regulated period of dehydration leading to the near total loss of water. When this occurs, the sub-cellular components become more crowded which may result in cell death. Therefore, seeds have developed "desiccation tolerance", the ability to withstand very low water levels. This has been connected to the build-up of many protective compounds including proteins and sugars. Among these are the late embryogenesis abundant (LEA) proteins which accumulate (as the name suggests) late in embryo development at the same time that the seed becomes desiccation tolerant. Previous work with a LEA protein, ATEM6, showed that the loss of this protein caused early drying of seeds at the far end of the seed pod. Here, we show that rehydrated, mature seeds from mutant plants (without ATEM6) lose more water during air drying than normal seeds. This result links the ATEM6 protein to water binding and water loss during embryo maturation. This work is very important because it demonstrates that the ATEM6 protein protects seeds from the loss of water during development. Studies such as these are helping to uncover how plants lose water, and we are learning how to prevent drought stress in agriculturally important crops.
Technical Abstract: The end of orthodox seed development is typified by a developmentally regulated period of dehydration leading to the loss of bulk water from the entire structure. When dehydration occurs, the cytoplasm condenses and intracellular components become more crowded, providing an environment amenable to numerous undesirable interactions that can lead to protein aggregation, denaturation, and organelle-cell membrane fusion. Acquisition of desiccation tolerance or the ability to withstand these very low water potentials and consequent molecular crowding has been correlated with the accumulation of various protective compounds including proteins and sugars. Among these are the late embryogenesis abundant (LEA) proteins, a diverse class of highly abundant, heat-stable proteins that accumulate late in embryo maturation coincident with the acquisition of desiccation tolerance. Previous work led us to hypothesize that the protein ATEM6, one of the two Arabidopsis thaliana group 1 LEA proteins, is involved in regulating the rate at which water is lost from the maturing embryo; homozygous atem6-1 mutants display premature dehydration of seeds at the distal end of the silique. Here, we demonstrate that rehydrated, mature seeds from atem6-1 mutant plants lose more water during subsequent air drying than wild-type seeds consistent with a role for ATEM6 protein in water binding/loss during embryo maturation. In addition and possibly as a result of premature dehydration, mutant seeds along the entire length of the silique acquire desiccation tolerance earlier than their wild-type counterparts. We further demonstrate the precocious and perhaps elevated expression of the other A. thaliana group 1 LEA protein, ATEM1, that compensate for loss or ATEM6 expression. However, this observation could also be consistent with the acceleration of the entire normal maturation program in atem6-1 mutant embryos. Interestingly, ATEM6 protein does not appear to be required in mature seeds for viability or efficient germination.