Identification of drought-induced genes in giant leucaena (Leucaena leucocephala subsp. glabrata)

A number of drought-induced genes have been identified from giant leucaena. Leucaena leucocephala subspecies glabrata (leucaena), which is also known as ‘giant leucaena’, is a multipurpose tree legume that can be grown and maintained as a woody tree for wood and paper pulp production, or as a shrubby legume through repeated harvest of foliage for use as a fodder. Leucaena is naturally resistant to most biotic and abiotic stresses including drought. The objective of this research was to identify drought-responsive genes in leucaena seedlings through microarray and qRT-PCR analyses. Ten thousand cDNA sequences selected from a leucaena transcriptome were screened for higher expression in a 4 × 180 k microarray using RNA isolated from drought-treated and untreated leucaena seedlings. Microarray analysis identified 73 and 39 drought-responsive genes sequences that were upregulated in the root and shoot, respectively. qRT-PCR analyses confirmed the root- and shoot-specific upregulation of some of the most highly expressed gene sequences identified in the microarray analysis. The proteins encoded by these genes could be grouped into four classes: (1) receptors that sense osmotic and oxidative stresses, (2) transcription factors, (3) degradation pathway enzymes, and (4) biosynthetic enzymes and structural proteins. The functions of these four classes of proteins can be used to explain the drought response in leucaena. The NB-LRR class of disease-resistance proteins may serve as receptors for detecting osmotic and oxidative stresses induced by drought, leading to induction of transcription factors such as zinc finger CCCH domain-containing protein and TCP14. As result, the genes for some degradative pathway enzymes, such as GDSL esterase/lipase, lipid acyl hydrolase patatin, and serine carboxypeptidase, were induced. Similarly, the expression of certain biosynthetic enzymes and structural proteins such as flavonoid 3-O-galactosyl transferase, caffeoyl-CoA O-methyltransferase, 9-cis-epoxy carotenoid dioxygenase, β-amyrin synthase, pentatricopeptide-containing protein, GPI-anchored protein COBRA, and peroxin, were also induced. High expression of some of these drought-inducible genes in leucaena seedlings may be used as a selection criterion in future breeding programs for drought resistance in leucaena and other legumes.