AUTHOR=Li Sibei , Devi Bhaswati , Allam Gamalat , Bhullar Armaan , Murmu Jhadeswar , Li Eryang , Hepworth Shelley R. 

TITLE=Regulation of secondary growth by poplar BLADE-ON-PETIOLE genes in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1244583

DOI=10.3389/fpls.2023.1244583

ISSN=1664-462X

ABSTRACT=<p><italic>BLADE-ON-PETIOLE</italic> (<italic>BOP</italic>) genes are essential regulators of vegetative and reproductive development in land plants. First characterized in <italic>Arabidopsis thaliana</italic> (Arabidopsis), members of this clade function as transcriptional co-activators by recruiting TGACG-motif binding (TGA) basic leucine zipper (bZIP) transcription factors. Highly expressed at organ boundaries, these genes are also expressed in vascular tissue and contribute to lignin biosynthesis during secondary growth. How these genes function in trees, which undergo extensive secondary growth to produce wood, remains unclear. Here, we investigate the functional conservation of <italic>BOP</italic> orthologs in <italic>Populus trichocarpa</italic> (poplar), a widely-used model for tree development. Within the poplar genome, we identified two <italic>BOP</italic>-like genes, <italic>PtrBPL1</italic> and <italic>PtrBPL2</italic>, with abundant transcripts in stems. To assess their functions, we used heterologous assays in Arabidopsis plants. The promoters of <italic>PtrBPL1</italic> and <italic>PtrBPL2</italic>, fused with a β-glucuronidase (GUS) reporter gene showed activity at organ boundaries and in secondary xylem and phloem. When introduced into Arabidopsis plants, <italic>PtrBPL1</italic> and <italic>PtrBPL2</italic> complemented leaf and flower patterning defects in <italic>bop1 bop2</italic> mutants. Notably, Arabidopsis plants overexpressing <italic>PtrBPL1</italic> and <italic>PtrBPL2</italic> showed defects in stem elongation and the lignification of secondary tissues in the hypocotyl and stem. Finally, PtrBPL1 and PtrBPL2 formed complexes with TGA bZIP proteins in yeast. Collectively, our findings suggest that PtrBPL1 and PtrBPL2 are orthologs of Arabidopsis BOP1 and BOP2, potentially contributing to secondary growth regulation in poplar trees. This work provides a foundation for functional studies in trees.</p>