LEA proteins in higher plants: Structure, function, gene expression and regulation

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Abstract

Late embryogenesis abundant (LEA) proteins are mainly low molecular weight (10–30 kDa) proteins, which are involved in protecting higher plants from damage caused by environmental stresses, especially drought (dehydration). These findings and the fact that the breeding of drought tolerant varieties would be of great value in agriculture, form the basis of search for anti-drought inducible genes and their characterization. LEA proteins are generally classified into six groups (families) according to their amino acid sequence and corresponding mRNA homology, which are basically localized in cytoplasm and nuclear region. LEA protein synthesis, expression and biological activities are regulated by many factors (e.g. developmental stages, hormones, ion change and dehydration), signal transduction pathways and lea genes. No tissue-specific lea gene expression has been considered as one main regulatory mechanism on the basis of extensive studies with the model plant, Arabidopsis thaliana. The study of the regulatory mechanism of lea gene expression is an important feature of modern plant molecular biology.

Introduction

Higher plants dominate terrestrial ecosystems and play most important economic and social roles in human life [1], [2], which contribute to their strong adaptive ability owing to a long period of evolution under the pressure of natural and human selection [3], [4]. During such time span, higher plants have developed multi-pathway, multi-level and multi-scale survival strategies for continual changes in the environment, which include anatomical, physiological, biophysical, biochemical, genetic, developmental and reproductive biological changes in response to adverse conditions [5]. The evolution of LEA proteins is one of these changes, which plays an important role in resistance to drought. This implies that studies on tolerant proteins, and the isolation, identification and functional analysis of their genes will be of great benefit to the breeding of drought-resistant crops [6], [7], [47], [48], [49], [50], [51], [52]. It is common knowledge that drought related food shortages is a worldwide problem. Especially in sub-Saharan Africa [8], [9], [47], [48], [49], [50], [51], [52]. Drought is one of the main factors limiting crop production [10], [11], [12], [13], [14], [15], [16]. Research on the biology and genetics of drought resistance and breeding of drought-resistant crops have, thus, become important field of contemporary research in plant molecular biology and molecular breeding. These efforts have been greatly aided by the sequencing of the Arabidopsis thaliana genome [6], [17], [18]. Here, we discuss the role of LEA protein structure, function and gene expression in the development of drought-resistant crops.

Section snippets

LEA protein distribution and types in higher plants

LEA proteins are formed during the late period of seed development accompanied by dehydration. They are proteins with small molecular weight ranging mainly from 10 to 30 kDa and above 30 kDa [19]. Dure and Croud [17] first studied LEA proteins in developing cotton seeds. Subsequently, researchers detected their existence in wheat, barley, maize, rice, sunflower, potato, grape, apple, bean, Arabidopsis, tomato, rye, soybean, carrot and so on [19], [20], [21], [22], [23], [24], [25], [26], [27],

LEA protein structure

LEA proteins in higher plants are mainly composed of hydrophilic amino acids ordered in repeated sequence (e.g. Gly and Lys), forming hyper-hydrophilicness and thermal stability. Advanced structure of such protein contains non-periodic linear and α-helixed structure without thermal dominative state and corresponding dehydrated proteins exist in a natural form of dimers.

Group 1 proteins (such as D19) have a conservative sequence made up of 20 amino acid residues in repeated copies, which can

LEA protein functions

LEA proteins mainly play functions in dehydration tolerance and storage of seeds and in whole-plant stress resistance to drought, salt, and cold. Farrant et al. (1992) experimented on the recalcitrant seeds of Avicennia marina and Podocarpus henkelii and concluded that one of the important reasons was the absence of LEA proteins in dehydration sensitive seeds. Further study showed that LEA proteins are expressed through all the developmental stages with different expression levels and no tissue

Gene expression and regulation of LEA proteins in higher plants

LEA protein gene expression in terms of time course starts from the late period of maturation and initiation period of drying reaches its peak in progressive dehydration and sharply decreases after some hours of germination [19], [23], [27], [38]. Many reports show that LEA protein gene expression has no tissue-specificity at the levels of tissues and organs as the gene can express in cotyledons, panicles of seeds [26] and also in stems, leaves and roots (vegetative tissues) [16], [18], [28],

Summary and perspective

Over the past 10 years, many advances have taken place in this challenging field. Although many molecular aspects are from the model plant A. thaliana, these have indeed deepened our understanding of higher plant resistance to drought. This anti-drought character is a quantitative character controlled by many genes and impacted by a large number of environmental, anatomical, physiological, biophysical, biochemical and developmental factors. The characteristic result we observe under a given

Acknowledgements

This work is jointly supported by State Key Basic Research Development Plan of China (G2000018605), Major Research Program of NSFC (90102012), Knowledge Innovation Engineering of the Chinese Academy of Sciences (KZCX1-06-2-4), Shao MA-Innovation Group Program Project of Northwestern Sci-tech University of Agriculture and Forestry, Doctoral Initiation Foundation of Chongqing University of Posts & Telecommunications and West-China Key Research Project of National Natural Science Foundation of

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