Cotton Late Embryogenesis Abundant (<i>LEA2)</i>Genes Promote Root Growth and Confer Drought Stress Tolerance in Transgenic<i>Arabidopsis thaliana</i>

Abstract

Late embryogenesis abundant (LEA) proteins play key roles in plant drought tolerance. In this study, 157, 85 and 89 candidate LEA2 proteins were identified in <i>G. hirsutum</i>, <i>G. arboreum</i> and <i>G. raimondii</i> respectively. <i>LEA2</i> genes were classified into 6 groups, designated as group 1 to 6. Phylogenetic tree analysis revealed orthologous gene pairs within the cotton genome. The cotton specific LEA2 motifs identified were E, R and D in addition to Y, K and S motifs. The genes were distributed on all chromosomes. LEA2s were found to be highly enriched in non-polar, aliphatic amino acid residues, with leucine being the highest, 9.1% in proportion. The miRNA, ghr-miR827a/b/c/d and ghr-miR164 targeted many genes are known to be drought stress responsive. Various stress-responsive regulatory elements, ABA-responsive element (ABRE), Drought-responsive Element (DRE/CRT), MYBS and low-temperature-responsive element (LTRE) were detected. Most genes were highly expressed in leaves and roots, being the primary organs greatly affected by water deficit. The expression levels were much higher in <i>G. tomentosum</i> as opposed to <i>G. hirsutum</i> The tolerant genotype had higher capacity to induce more of <i>LEA2</i> genes. Over expression of the transformed gene <i>Cot_AD24498</i> showed that the <i>LEA2</i> genes are involved in promoting root growth and in turn confers drought stress tolerance. We therefore infer that <i>Cot_AD24498</i>, <i>CotAD_20020</i>, <i>CotAD_21924</i> and <i>CotAD_59405</i> could be the candidate genes with profound functions under drought stress in upland cotton among the <i>LEA2</i> genes. The transformed <i>Arabidopsis</i> plants showed higher tolerance levels to drought stress compared to the wild types. There was significant increase in antioxidants, catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) accumulation, increased root length and significant reduction in oxidants, Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations in the leaves of transformed lines under drought stress condition. This study provides comprehensive analysis of LEA2 proteins in cotton thus forms primary foundation for breeders to utilize these genes in developing drought tolerant genotypes.