Characterization of silicon transporter gene family in Saccharum and functional analysis of the ShLsi6 gene in biotic stress.

Silicon, one of the most prevalent elements in the soil, is beneficial for plant growth and defense against different stresses. The silicon transporter gene (Lsi) plays an important role in the uptake and transport of silicon in higher plants. In this study, a total of 32 Lsi genes, including 20 SsLsi in sugarcane wild species Saccharum spontaneum, 5 ShLsi in Saccharum hybrid cultivar R570 and 7 SbLsi in sugarcane related species Sorghum bicolor, were identified and classified into three groups. Bioinformatics analysis showed that instability, hydrophobicity, localization of cell membranes and vacuoles were the main features of the Lsi proteins. Whole genome and segmental duplication contributed to the main expansion of Lsi gene family. Collinearity analysis of the Lsi genes showed that S. spontanum and R570 had a collinear relationship with monocotyledonous plants S. bicolor and Oryza sativa, but not with dicotyledonous plants Arabidopsis thaliana and Vitis vinifera. The replicated Lsi genes were mainly subjected to strong selection pressure for purification. The diverse cis-regulatory elements in the promoter of SsLsi, ShLsi and SbLsi genes suggested that they were widely involved in the response of plants to various stresses and the regulation of the growth and development. Transcriptome data and real time quantitative PCR analysis showed that the Lsi genes exhibited different expression profiles in sugarcane tissues and under Sporisorium scitamineum, drought and cold stresses. In addition, the cDNA and genomic DNA sequences of ShLsi6 that was homologous to SsLsi1b gene was cloned from Saccharum hybrid cultivar ROC22. Transient expression analysis showed that, compared with the control, Nicotiana benthamiana leaves which overexpressed the ShLsi6 gene showed a high sensitivity after inoculation with tobacco pathogens Ralstonia solanacearum and Fusarium solani var. coeruleum. This study provides important information for further functional analysis of Lsi genes and resistant breeding in sugarcane.

Genome-wide identification and expression analysis of the coronatine-insensitive 1 (COI1) gene family in response to biotic and abiotic stresses in Saccharum.

BACKGROUND: The coronatine insensitive 1 (COI1) gene is the core member of jasmonate signaling pathway, which is closely related to plant biotic and abiotic resistance. However, there have been no reports on COI1 in sugarcane (Sacharum spp.). Hence, systematically investigating the characteristics of the COI1 multigene family in sugarcane can provide a means to study and manipulate the jasmonic acid signaling pathway. RESULTS: A total of 156 COI1 proteins were obtained from the genomes of 19 land plants, while none were obtained from five algae species. A phylogenetic tree demonstrated that these COI1 proteins were classified into four groups, while 31 proteins of SsCOI1 from Saccharum spontaneum, SbCOI1 from Sorghum bicolor, and ShCOI1 from Saccharum spp. hybrid cultivar R570 clustered into three groups. Synteny analysis and duplication patterns revealed that COI1 genes expanded through various genome replication events and could have experienced strong purifying selective pressure during evolution in S. spontaneum, S. bicolor, and R570. An investigation of cis-acting elements suggests that COI1 genes may be involved in plant growth and development and response to various stresses. Expression analysis implied that 21 SsCOI1 genes were constitutively expressed, and had positive responses to drought, cold, and Sporisorium scitamineum stresses with different expression patterns. Among them, seven SsCOI1 haplotype genes may play different roles in response to methyl jasmonate. Furthermore, the ShCOI1-4, ShCOI1-5, and ShCOI1-6 genes were cloned from Saccharum spp. hybrid cultivar ROC22. Real-time quantitative PCR (RT-qPCR) analysis demonstrated that these three ShCOI1 genes had divergent expression profiles in response to salicylic acid, abscisic acid, polyethylene glycol, cold, and S. scitamineum. CONCLUSIONS: These results suggest that COI1 genes may act in sugarcane growth, development, and response to various stresses via different regulatory mechanisms, which laying a foundation for the functional identification of the sugarcane COI1 gene.

ScAOC1, an allene oxide cyclase gene, confers defense response to biotic and abiotic stresses in sugarcane.

KEY MESSAGE: An allene oxide cyclase gene which is involved in defense against biotic and abiotic stresses was cloned and characterized in sugarcane. Allene oxide cyclase (AOC), a key enzyme in jasmonate acid (JA) biosynthesis, affects the stereoisomerism and biological activity of JA molecules, and plays an important role in plant stress resistance. In this study, four SsAOC alleles (SsAOC1-SsAOC4), which shared similar gene structure and were located on Chr1A, Chr1B, Chr1C, and Chr1D, respectively, were mined from sugarcane wild species Saccharum spontaneum, and a homologous gene ScAOC1 (GenBank Accession Number: MK674849) was cloned from sugarcane hybrid variety Yacheng05-179 inoculated with Sporisorium scitamineum for 48 h. ScAOC1 and SsAOC1-SsAOC4 were alkaline, unstable, hydrophilic, and non-secretory proteins, which possess the same set of conserved motifs and were clustered into one group in the phylogenetic analysis. ScAOC1 was expressed in all sugarcane tissues, but with different levels. After infection by S. scitamineum, the transcripts of ScAOC1 were increased significantly both in the smut-susceptible (ROC22) and resistant (Yacheng05-179) varieties, but its transcripts were more accumulated and lasted for a longer period in the smut-resistant variety than in the smut-susceptible one. ScAOC1 was down-regulated under MeJA and NaCl treatments, but up-regulated under SA, ABA, PEG, and cold stresses. Transiently overexpressing ScAOC1 gene into Nicotiana benthamiana leaves regulated the responses of N. benthamiana to two pathogens Ralstonia solanacearum and Fusarium solani var. coeruleum. Furthermore, prokaryotic expression analysis showed overexpression of ScAOC1 in Escherichia coli BL21 could enhance its tolerance to NaCl, mannitol, and cold stimuli. These results indicated that ScAOC1 may play an active role in response to biotic and abiotic stresses in sugarcane.