Abstract
Miscanthus is a promising lignocellulosic bioenergy crop for bioethanol production. To identify candidate genes and regulation networks involved in secondary cell wall (SCW) development in Miscanthus, we performed de novo transcriptome analysis of a developing internode. According to the histological and in-situ histochemical analysis, an elongating internode of M. lutarioriparius can be divided into three distinct segments, the upper internode (UI), middle internode (MI) and basal internode (BI), each representing a different stage of SCW development. The transcriptome analysis generated approximately 300 million clean reads, which were de novo assembled into 79,705 unigenes. Nearly 65% of unigenes was annotated in seven public databases. Comparative profiling among the UI, MI and BI revealed four distinct clusters. Moreover, detailed expression profiling was analyzed for gene families and transcription factors (TFs) involved in SCW biosynthesis, assembly and modification. Based on the co-expression patterns, putative regulatory networks between TFs and SCW-associated genes were constructed. The work provided the first transcriptome analysis of SCW development in M. lutarioriparius. The results obtained provide novel insights into the biosynthesis and regulation of SCW in Miscanthus. In addition, the genes identified represent good candidates for further functional studies to unravel their roles in SCW biosynthesis and modification.
Highlights
Miscanthus is a perennial C4 rhizomatous grass originated from eastern and southern Asia
IREGULAR XYLEM (IRX) 9 and IRX14 from GT43 family, and IRX10 from GT47 family are required for the elongation of the xylan backbone[17,18,19,20], whereas FRAGILE FIBER (FRA) 8/IRX7 from GT47 family, IRX8 and PARVUS from GT8 family are involved in the synthesis of the reducing-end tetrasaccharide of xylan[21,22,23]
The results showed that a total of 78 transcription factors (TFs) belonging to 17 different families were preferentially expressed in the middle internode (MI) and basal internode (BI) compared to the upper internode (UI), suggesting putative roles in the regulation of secondary cell wall (SCW) formation (Fig. 7H)
Summary
Miscanthus is a perennial C4 rhizomatous grass originated from eastern and southern Asia. Lignin biosynthesis has been well-characterized and almost all the genes for each step of the monolignol biosynthetic pathway have been identified by utilizing reverse genetic approaches and biochemical assays in different plant species[24]. Besides these major components, SCWs contain a minor proportion of structural proteins. The KORRIGAN (KOR) protein from GH9 family has been revealed to play an important role in cellulose biosynthesis It might function in the cleavage of a sterol-cellodextrin precursor or assist in the assembly of glucan chains in the growing microfibrils[29, 30]. Several members from GH10 and GH11 families are considered to catalyze the modification and degradation of hemicelluloses (e.g., xyloglucan and xylan)[31, 32]
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