AUTHOR=Zhou Houjun , Song Xueqin , Lu Meng-Zhu 

TITLE=Growth-regulating factor 15-mediated vascular cambium differentiation positively regulates wood formation in hybrid poplar (Populus alba × P. glandulosa)

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1343312

DOI=10.3389/fpls.2024.1343312

ISSN=1664-462X

ABSTRACT=<sec><title>Introduction</title><p>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.</p></sec><sec><title>Methods</title><p>In this study, <italic>mPagGRF15</italic> OE and <italic>PagGRF15-SRDX</italic> transgenic poplars were generated to investigate the function of <italic>PagGRF15</italic>. 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 <italic>PagGRF15</italic>.</p></sec><sec><title>Results and discussion</title><p>We report that <italic>PagGRF15</italic> from hybrid poplar (<italic>Populus alba</italic> × <italic>P. glandulosa</italic>), a growth-regulating factor, plays a critical role in the regulation of vascular cambium activity. <italic>PagGRF15</italic> was expressed predominantly in the cambial zone of vascular tissue. Overexpression of <italic>mPagGRF15</italic> (the mutated version of <italic>GRF15</italic> in the <italic>miR396</italic> target sequence) in Populus led to decreased plant height and internode number. Further stem cross sections showed that the <italic>mPagGRF15</italic> 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 <italic>mPagGRF15</italic> OE plants. However, dominant suppression of the downstream genes of <italic>PagGRF15</italic> using <italic>PagGRF15-SRDX</italic> showed an opposite phenotype. Based on the RNA-seq and ChIP-seq results, combining qRT-PCR and ChIP-PCR analysis, candidate genes, such as <italic>WOX4b</italic>, <italic>PXY</italic> and <italic>GID1.3</italic>, were obtained and found to be mainly involved in cambial activity and xylem differentiation. Accordingly, we speculated that <italic>PagGRF15</italic> functions as a positive regulator mediating xylem differentiation by repressing the expression of the <italic>WOX4a</italic> and <italic>PXY</italic> genes to set the pace of cambial activity. In contrast, <italic>PagGRF15</italic> mediated the GA signaling pathway by upregulating <italic>GID1.3</italic> 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.</p></sec>