A comprehensive survey of the aldehyde dehydrogenase gene superfamily in Saccharum and the role of ScALDH2B-1 in the stress response

Aldehyde dehydrogenases (ALDHs) belong to NAD(P)+-dependent enzymes and are considered ‘‘aldehyde scavengers’’. They play crucial roles in growth, development, and environmental stress adaptation in plants. In this study, a total of 70 SsALDH and 14 ShALDH superfamily genes were identified in Saccharum spontaneum and Saccharum spp. R570 cultivar, respectively. Results showed that the SsALDH superfamily was classified into 10 ALDH families, and the ShALDH superfamily was divided into eight ALDH families. A co-expression network analysis suggested that these ALDH proteins may play vital roles in the stress response due to the fact that they are involved in the metabolism of proline, γ-aminobutyrate, and lysine. The promotor cis-element prediction revealed that the ALDH genes may be regulated by many phytohormones and are involved in various stress responses. RNA-seq data and qRT-PCR analysis inferred that ALDH genes in Saccharum played various roles in response to drought, cold and Sporisorium scitamineum stresses, and they were constitutively expressed in different sugarcane tissues. Additionally, an expression analysis of ScALDH2B-1 suggested significant changes under various stresses. The prokaryotic expression of ScALDH2B-1 in Escherichia coli BL21 cells resulted in enhanced tolerance to salinity. The ectopic expression of ScALDH2B-1 in Nicotiana benthamiana showed that, after challenged by Fusarium solani var. coeruleum, several HR maker genes were upregulated, while the accumulation of H2O2 and HR-like cell death were triggered. A working model of the function of ALDHs in the Saccharum species was thus proposed. This study contributes to our understanding of the evolution and function of ALDH superfamily genes in Saccharum, and it also provides a baseline for the function identification of ScALDH2B-1 under biotic stress.