Overexpression of a Prefoldin β subunit gene reduces biomass recalcitrance in the bioenergy crop Populus.

Jin Zhang,Gerald A Tuskan,Jeremy Schmutz,Kimberly A Winkeler,Jinhua Ding,Nancy L Engle,Mi Li,Kerrie Barry,Meng Xie,Cassandra M Collins,Vasanth Singan,Anthony C Bryan,Xiaohan Yang,Wellington Muchero,Timothy J Tschaplinski,Yunqiao Pu,Lee E Gunter ,William H Rottmann ,Sara Jawdy ,Erika Lindquist ,Jay Chen

doi:10.1111/pbi.13254

Abstract

SummaryPrefoldin (PFD) is a group II chaperonin that is ubiquitously present in the eukaryotic kingdom. Six subunits (PFD1‐6) form a jellyfish‐like heterohexameric PFD complex and function in protein folding and cytoskeleton organization. However, little is known about its function in plant cell wall‐related processes. Here, we report the functional characterization of a PFD gene from Populus deltoides, designated as PdPFD2.2. There are two copies of PFD2 in Populus, and PdPFD2.2 was ubiquitously expressed with high transcript abundance in the cambial region. PdPFD2.2 can physically interact with DELLA protein RGA1_8g, and its subcellular localization is affected by the interaction. In P. deltoides transgenic plants overexpressing PdPFD2.2, the lignin syringyl/guaiacyl ratio was increased, but cellulose content and crystallinity index were unchanged. In addition, the total released sugar (glucose and xylose) amounts were increased by 7.6% and 6.1%, respectively, in two transgenic lines. Transcriptomic and metabolomic analyses revealed that secondary metabolic pathways, including lignin and flavonoid biosynthesis, were affected by overexpressing PdPFD2.2. A total of eight hub transcription factors (TFs) were identified based on TF binding sites of differentially expressed genes in Populus transgenic plants overexpressing PdPFD2.2. In addition, several known cell wall‐related TFs, such as MYB3, MYB4, MYB7, TT8 and XND1, were affected by overexpression of PdPFD2.2. These results suggest that overexpression of PdPFD2.2 can reduce biomass recalcitrance and PdPFD2.2 is a promising target for genetic engineering to improve feedstock characteristics to enhance biofuel conversion and reduce the cost of lignocellulosic biofuel production.

Highlights

A protein’s function is partially controlled by its three-dimensional structure and is dependent on a complex network of molecular chaperones (Kim et al, 2013)
We describe the characterization of a PFD b subunit gene in Populus deltoides, PdPFD2.2, encoded by the locus Potri.008G153900
Except for Arabidopsis PDF2, the PFD2 genes from woody dicots, herbaceous dicots, monocots and moss were grouped into different clades (Figure 1a), which implies that their functions might have been diverged during evolution

Summary

Introduction

A protein’s function is partially controlled by its three-dimensional structure and is dependent on a complex network of molecular chaperones (Kim et al, 2013). PFD is classified as a group II chaperonin, which is found in archaea and eukaryotes and appears to be central to a complex network of co-chaperones. Eukaryotic PFD is polymeric and consists of six subunits: two a subunits (PFD3 and PFD5) and four b subunits (PFD1, PFD2, PFD4 and PFD6) (Siegert et al, 2000). These six subunits form a ‘jellyfish-like’ heterohexameric complex, which can deliver newly synthesized unfolded protein to cytosolic chaperonins containing TCP-1 for protein folding and protecting unfolded proteins in this process (Siegert et al, 2000)

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Discussion

Conclusion