Isolation and expression of Lea gene in desiccation-tolerant microspore-derived embryos in Brassica spp.
Desiccation tolerance can be induced in microspore-derived embryos of Brassica spp. by application of abscisic acid (ABA). As part of our effort to elucidate the molecular mechanism in induction of desiccation tolerance of embryos, we have isolated Lea genes and examined their expression in microspore-derived embryos of B. napus and B. campestris. The cDNA clones of Lea genes were isolated from desiccation-tolerant microspore-derived embryos of both species. Two cDNA clones of B. napus and B. campestris shared a similar homology of 92.9% identity between the two deduced proteins. These proteins also had high homology with Lea 76 which was isolated from zygotic embryos of B. napus, but were 54 amino acids shorter than Lea 76. Acquisition of desiccation tolerance of the microspore-derived embryos and accumulation of mRNA and its transcripts of the Lea genes began within 12 h of ABA treatment. The embryos treated with ABA for 48-168 h showed a high desiccation tolerance and accumulation of Lea proteins at high levels. The close relationships between the induction of desiccation tolerance of embryos and the expression level of Lea genes suggest an important function of Lea proteins for desiccation tolerance in embryos.