Abstract
Late Embryogenesis Abundant (LEA) proteins are an ubiquitous group of polypeptides that were first described to accumulate during plant seed dehydration, at the later stages of embryogenesis. Since then they have also been recorded in vegetative plant tissues experiencing water limitation and in anhydrobiotic bacteria and invertebrates and, thereby, correlated with the acquisition of desiccation tolerance. This study provides the first comprehensive study about the LEA gene family in sweet orange (Citrus sinensis L. Osb.), the most important and widely grown fruit crop around the world. A surprisingly high number (72) of genes encoding C. sinensis LEAs (CsLEAs) were identified and classified into seven groups (LEA_1, LEA_2, LEA_3 and LEA_4, LEA_5, DEHYDRIN and SMP) based on their predicted amino acid sequences and also on their phylogenetic relationships with the complete set of Arabidopsis thaliana LEA proteins (AtLEAs). Approximately 60% of the CsLEAs identified in this study belongs to the unusual LEA_2 group of more hydrophobic LEA proteins, while the other LEA groups contained a relatively small number of members typically hydrophilic. A correlation between gene structure and motif composition was observed within each LEA group. Investigation of their chromosomal localizations revealed that the CsLEAs were non-randomly distributed across all nine chromosomes and that 33% of all CsLEAs are segmentally or tandemly duplicated genes. Analysis of the upstream sequences required for transcription revealed the presence of various stress-responsive cis-acting regulatory elements in the promoter regions of CsLEAs, including ABRE, DRE/CRT, MYBS and LTRE. Expression analysis using both RNA-seq data and quantitative real-time RT-PCR (qPCR) revealed that the CsLEA genes are widely expressed in various tissues, and that many genes containing the ABRE promoter sequence are induced by drought, salt and PEG. These results provide a useful reference for further exploration of the CsLEAs functions and applications on crop improvement.
Highlights
Late Embryogenesis Abundant (LEA) proteins have been found to accumulate in tissues of plants exposed to stresses that include dehydration or during some stages of plant development involving water limitation, such as seed, pollen grain, shoot and root development [1]
Existing annotation in the sweet orange genome sequence database at Phytozome and BLAST searches using the 51 amino acid sequences of the complete set of A. thaliana LEA proteins (AtLEAs) as query sequences have resulted in the identification of a total of 72 different LEA encoding protein genes in C. sinensis (CsLEAs), which were distributed in seven distinct groups (LEA_1, LEA_2, LEA_3, LEA_4, LEA_5, DEHYDRIN and SMP) (S2 Table)
In order to compare the numbers of LEA genes within each group among the different species of higher plants, we searched the well-annotated genomes of Clementine mandarin (Citrus clementina), Arabidopsis (A. thaliana), rice (Oryza sativa), poplar (Populus trichocarpa) and grapevine (Vitis vinifera) available at Phytozome, using the same strategy as outlined for sweet orange
Summary
Late Embryogenesis Abundant (LEA) proteins have been found to accumulate in tissues of plants exposed to stresses that include dehydration or during some stages of plant development involving water limitation, such as seed, pollen grain, shoot and root development [1]. LEAs are widely distributed proteins in the plant kingdom, from algae to angiosperms, and they are found in anhydrobiotic invertebrates and in some bacterial species [1] They are mainly composed of hydrophilic amino acids arranged in repeated sequences, forming a highly hydrophilic structure and with thermal stability [5,6]. Mitochondria, protein and lipid bodies, plasmodesmata and nucleus [8]
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