Growth-regulating factor 15-mediated vascular cambium differentiation positively regulates wood formation in hybrid poplar ( × ).

INTRODUCTION

Hybrid poplars are industrial trees in China. An understanding of the molecular mechanism underlying wood formation in hybrid poplars is necessary for molecular breeding. Although the division and differentiation of vascular cambial cells is important for secondary growth and wood formation, the regulation of this process is largely unclear.

METHODS

In this study, OE and transgenic poplars were generated to investigate the function of . RNA-seq and qRT-PCR were conducted to analyze genome-wide gene expression, while ChIP‒seq and ChIP-PCR were used to identified the downstream genes regulated by .

RESULTS AND DISCUSSION

We report that from hybrid poplar ( × ), a growth-regulating factor, plays a critical role in the regulation of vascular cambium activity. was expressed predominantly in the cambial zone of vascular tissue. Overexpression of (the mutated version of in the target sequence) in Populus led to decreased plant height and internode number. Further stem cross sections showed that the OE plants exhibited significant changes in vascular pattern with an increase in xylem and a reduction in phloem. In addition, cambium cell files were decreased in the OE plants. However, dominant suppression of the downstream genes of using showed an opposite phenotype. Based on the RNA-seq and ChIP-seq results, combining qRT-PCR and ChIP-PCR analysis, candidate genes, such as , and , were obtained and found to be mainly involved in cambial activity and xylem differentiation. Accordingly, we speculated that functions as a positive regulator mediating xylem differentiation by repressing the expression of the and genes to set the pace of cambial activity. In contrast, mediated the GA signaling pathway by upregulating expression to stimulate xylem differentiation. This study provides valuable information for further studies on vascular cambium differentiation mechanisms and genetic improvement of the specific gravity of wood in hybrid poplars.