Root transcriptome of Arabidopsis thaliana mutant plants of the transcription factor AtHB23 under control and salinity conditions. Root transcriptome of Arabidopsis thaliana AtHB23 mutants under control and salinity conditions

The high plasticity of roots, the anchorage organs responsible for water and nutrient uptake, is governed by physiological, genetic, and epigenetic programs, enabling plant adaptation to different conditions. Transcription factors (TFs) and hormones are crucial players in regulating root architecture. AtHB23 is a TF belonging to the homeodomain-leucine zipper I family, previously characterized as a target of ARF7/19 and direct regulator of the auxin carrier LAX3 and the TF LBD16, modulating lateral root initiation and higher-order roots development. In this work, we report that the expression of AtHB23 is oppositely modulated in the main and lateral roots by NaCl. The silencing of this gene triggered a severe reduction in primary root length and a significant increment in the initiation of lateral roots. The opposite phenotype was observed when it was overexpressed. Moreover, in response to NaCl, amiR23-silenced plants exhibited a low survival rate compared to controls. In front of salinity, amiR23-silenced plants showed degraded starch granules and altered starch metabolism. AmiR23- silenced plants in NaCl did not recover in a normal medium by auxin or sucrose. The amiR23 differential phenotype involved the repression of the AtHB23-target, LAX3. Finally, a transcriptome analysis supported the observed phenotype depending on AtHB23 in salinity conditions. Altogether, the results showed here indicated that the presence of AtHB23 is vital for plant survival and adaptation to salt stress conditions, and its function is closely related to the gravitropic response mediated by starch granule turnover, involving the auxin carrier LAX3.