Gibberellin-deactivating GA2OX enzymes act as a hub for auxin-gibberellin crosstalk in Arabidopsis thaliana root growth regulation
We combined transcriptomic profiling of auxin related mutants with genetic and biochemical approaches and live-cell imaging techniques of Arabidopsis roots to understand the role of auxin-driven gibberellin level changes during root development, particularly root cell elongation. We show that auxin negatively regulates the level of gibberellin in root elongation zone. Auxin signalling steers the expression of gibberellin deactivating enzymes - GIBBERELLIN 2-OXIDASES (GA2OX) exclusively in root elongation zone. Interestingly, GA2OX8 expression is high in tissues with elevated auxin levels, such as vasculature or stem cell niche, fitting with the observed effect of auxin on gibberellin level. Here we show that GA2OX enzymes are negative regulators of root cell elongation. Gibberellin decrease caused by GA2OX8 overexpression inhibits root cell elongation. In contrast, roots missing GA2OX genes elongate faster. These findings indicate that GA2OX8 enzymes represent an integration core of auxin and gibberellin signalling pathway in root elongation zone, vascular development and regulation of stem cell niche. Our results enhance understanding of complex mechanisms controlling root cell elongation. Overall design: G1090::XVE>>AXR3-1(doi: 10.1038/nature13663), G1090::XVE>>?MP (doi: 10.3390/plants10112271) and Col-0 were grown on ½ MS plates for 5d and then whole plants were poured with 5ml of 2,5 µM estradiol-containing ½ MS liquid medium, making sure that all plants are treated. Additionally, all lines  were poured with dmso-containing ½ MS liquid medium. Leftover medium was removed, and plants grown vertically for 1.5h or 3h in cultivation room. After this, roots were harvested. To obtain transcriptomic data, RNA from 40-50 root tips (7-10 mm) of G1090::XVE>>AXR3-1, G1090::XVE>>?MP and Col-0 was extracted following the protocol (Plant Total RNA Mini Kit, Favorgen). cDNA library was prepared from polyA-enriched total RNA and sequenced by Illumina. The sequencing resulted in at least 20 million 150 bps long read pairs.