A New Calmodulin-Binding Protein Expresses in the Context of Secondary Cell Wall Biosynthesis and Impacts Biomass Properties in Populus

Abstract

A greater understanding of biosynthesis, signaling and regulatory pathways involved in determining stem growth and secondary cell wall chemistry is important for enabling pathway engineering and genetic optimization of biomass properties. The present study describes a new functional role of <i>PdIQD10</i>, a <i>Populus</i> gene belonging to the IQ67-Domain1 family of <i>IQD</i> genes, in impacting biomass formation and chemistry. Expression studies showed that <i>PdIQD10</i> has enhanced expression in developing xylem and tension-stressed tissues in <i>Populus deltoides</i>. Molecular dynamics simulation and yeast two-hybrid interaction experiments suggest interactions with two calmodulin proteins, CaM247 and CaM014, supporting the sequence-predicted functional role of the PdIQD10 as a calmodulin-binding protein. PdIQD10 was found to interact with specific <i>Populus</i> isoforms of the Kinesin Light Chain protein family, shown previously to function as microtubule-guided, cargo binding and delivery proteins in <i>Arabidopsis</i>. Subcellular localization studies showed that PdIQD10 localizes in the nucleus and plasma membrane regions. Promoter-binding assays suggest that a known master transcriptional regulator of secondary cell wall biosynthesis (PdWND1B) may be upstream of an <i>HD-ZIP III</i> gene that is in turn upstream of <i>PdIQD10</i> gene in the transcriptional network. RNAi-mediated downregulation of <i>PdIQD10</i> expression resulted in plants with altered biomass properties including higher cellulose, wall glucose content and greater biomass quantity. These results present evidence in support of a new functional role for an <i>IQD</i> gene family member, <i>PdIQD10</i>, in secondary cell wall biosynthesis and biomass formation in <i>Populus.</i>