Abstract
Pathogenesis-related protein 1 (PR-1) is an important defense protein stimulated by adverse environmental conditions and is used in plants as a molecular marker of systemic acquired resistance (SAR). Few information is available regarding the function and the expression pattern of the PR-1 gene in sugarcane (Saccharum spp. hybrids). In this study, 19 PR-1 genes (SsPR1.1-SsPR1.19) were identified in the genome of Saccharum spontaneum and these genes were distributed into three phylogenetic groups. A full-length cDNA clone of ScPR1 was obtained from sugarcane cultivar ROC22 and this clone shared highest homology of amino acids (83.5%) with SsPR1.14 of phylogenetic Group D. After infection with Acidovorax avenae subsp. avenae (Aaa), transcript expression of the ScPR1 gene was significantly upregulated (6.1-11.1) in ROC22 (resistant to Aaa). This gene was only upregulated 2.1-6.3 times in sugarcane cultivar MT11-610 (susceptible to Aaa) during a 24-72 h post-inoculation (hpi) period. ScPR1 was also upregulated in sugarcane tissues (root, stem, and leaf) under NaCl, PEG6000, and SA (salicylic acid) treatments in both cultivars, except for the stems of MT11-610 plants under PEG6000 stress and roots of the two cultivars under NaCl stress. Transgenic lines of Arabidopsis thaliana overexpressing ScPR1 were enhanced in tolerance to NaCl and mannitol dehydration stresses and to infection by the bacterial pathogen Pseudomonas syringae pv. tomato, strain DC3000 (Pst DC3000). Meanwhile, the transcript expressions of the defense genes (PR-3, PR-4, PR-5, and PDF1.2) involved in SA and JA/ET (jasmonic acid/ethylene) signaling pathways were also increased in these same Arabidopsis transgenic lines after Pst DC3000 attack. These findings suggest that the ScPR1 gene plays an important role in the regulation of tolerance to biotic and abiotic stresses in sugarcane, in Arabidopsis, and most likely in other plants.