Overexpression of from , a Non-Canonical / Gene, Specifically Decouples Lignification of the Different Cell-Types in Secondary Xylem.

Wood (secondary xylem) formation is regulated by auxin, which plays a pivotal role as an integrator of developmental and environmental cues. However, our current knowledge of auxin-signaling during wood formation is incomplete. Our previous genome-wide analysis of / in showed the presence of the non-canonical paralog member that is preferentially expressed in cambium. We analyzed its cellular localization using a GFP fusion protein and its transcriptional activity using transactivation assays, and demonstrated its nuclear localization and strong auxin response repressor activity. In addition, we functionally tested the role of by constitutive overexpression in to investigate for phenotypic changes in secondary xylem formation. Transgenic plants overexpressing were smaller and displayed impaired development of secondary fibers, but not of other wood cell types. The inhibition in fiber development specifically affected their cell wall lignification. We performed yeast-two-hybrid assays to identify protein partners during wood formation in , and identified EgrIAA9A, whose ortholog PtoIAA9 in poplar is also known to be involved in wood formation. Altogether, we showed that is an important auxin signaling component specifically involved in controlling the lignification of wood fibers.