Functional Analysis Of SbHLH1and SbLIM1Genes In Energy Sorghum (Sorghum Bicolor)

The rapid development of the global economy results in more and more serious energy exhaustion, which gives rise to increasing energy crisis around the world, with a more severe situation in China. Developing bioenergy vigorously, especially cellulosic ethanol industry, is a perspective way to solve this problem. Sorghum has multiple resistance and strong adaptability, and is therefore an ideal energy crop. Reducing lignin content in plant cell walls is one of critical approaches to improve the efficiency of lignocellulose enzymatic hydrolysis, increase ethanol production and reduce costs. Brown midrib mutants (bmr) of sorghum has a low lignin content, and is a good material to understand the regulatory mechanism of lignin biosynthesis in plants.In this work, we firstly analyzed the contents of total lignins, the phenotypes, and the transcriptional profiles of SbLIM1and other genes that are involved in lignin synthesis from nine bmr mutant plants. The leaves of plants at both five-leaf and seven-leaf stages as well as the stems of plants at seven-leaf stage were sampled for analysis. The distinguished difference in these indices was found among the mutant lines, indicating that their mutant genes are not genetically allelic with each other. The lignin contents are not strictly consistent with the appearance time and the brown shape of bmr phenotype, and the transcript abundances of SbLIMl are also not closely relative with the lignin contents in the leaves.The product of SbHLH1is localized in the nucleus, cytoplasm and cell membrane. The overexpression of SbHLHl in Arabidopsis induces the transcription of MYB46, MYB83, MYB63and F5H (AT5G04330.1), but has no effect on the expression of other lignin synthesis associated genes. This indicates that SbHLHl transcription factor may regulate the content of total lignin through a novel unknown mechanism beyond the NST/MYB pathway, but it accounts for the change of lignin composition via modulating the activity of F5H through the NST/MYB pathway. There have notably lower contents of total flavonoids in SbHLHl overexpressors than in the wildtype plants, but the contents of anthocyanins are comparable. The SbHLH1transgenic plants are lodging, and their other developmental and reproductive phenotypes are similar to the wild type.The expression of SbLIM1is up-regulated in some bmr mutants. The mutant of AtLIMl, a homologous gene of SbLIM1in Arabidopsis, significantly lowered the content of total lignins. The ectopic expression of SbLIMl in Arabidopsis results in the decrease in the lignin content and the increase in AtLIMl expression, indicating that AtLIMl may be regulated by SbHLH1.Besides, we also compared the allelic variations of four important genes (the waterlogging-enduring gene SbSUB, stem sugar accumulation associated ethylene receptor gene SbSBER, stress tolerance gene SbSRO, and lignin synthesis related transcription factor gene SbLIM1) between Sorghum BTX623, the cultivar for genome sequencing, and three sorghum cultivars (Red yingzi,Danzhai and Kaili) from Guizhou province. In comparison with BTX623, the coding regions and promoters of these four genes have many SNP and INDEL variations, of which SbSUB, SbSBER, SbLIM1have seven, seven, and three SNP sites, respectively, but how these variations are taken place as well as their impacts on gene function need to be further analyzed.