Enhanced drought and salinity tolerance in transgenic mustard [Brassica juncea (L.) Czern & Coss.] overexpressing Arabidopsis group 4 late embryogenesis abundant gene (AtLEA4-1)

Abstract

Indian mustard [Brassica juncea (L.) Czern & Coss.] is one of the most important oilseed crop worldwide, yet relatively mild drought and salinity stress significantly reduce its growth and yield. Expression of LEA (Late Embryogenesis Abundant) proteins was previously shown to alleviate osmotic stress by stabilizing water status, protecting cytosolic structures and cell through increased membrane and protein stability. We overexpressed Arabidopsis group 4 LEA protein AtLEA4-1 in mustard, resulting the transgenic lines to show enhanced drought and salinity tolerance. Southern hybridization showed the copy number of the gene inserted into the transgenics while, qRT PCR determined the transcript level of the overexpressed gene. Leaf senescence assay showed better adaptability of the transgenics to both salt and PEG stress, as revealed by increased chlorophyll content in the transgenic plants when compared to wild type. The transgenic mustard plants showed better survivability under both drought and salinity stress in soil. Physiological analysis revealed lower levels of lipid peroxidation, hydrogen peroxide and oxygen radical production but higher levels of relative water content (RWC) in T1 transgenic AtLEA4-1 lines with not so significant increase in proline content. Antioxidative enzyme activities showed better adaptation of transgenic plants to drought stress. Even when the biochemical parameters were analysed as a function of RWC, the transgenic plant tissues showed improved adaptation to drought and salinity stress depicting, the functions of LEA proteins as antioxidant and molecular chaperone exerting equivalent impact as that of hydration buffer towards abiotic stress tolerance.