The Transcription Factor ATHB5 Affects GA-Mediated Plasticity in Hypocotyl Cell Growth during Seed Germination

Abstract

Gibberellic acid (GA)-mediated cell expansion initiates the seed-to-seedling transition in plants and is repressed by DELLA proteins. Using digital single-cell analysis, we identified a cellular subdomain within the midhypocotyl, whose expansion drives the final step of this developmental transition under optimal conditions. Using network inference, the transcription factor ATHB5 was identified as a genetic factor whose localized expression promotes GA-mediated expansion specifically within these cells. Both this protein and its putative growth-promoting target EXPANSIN3 are repressed by DELLA, and coregulated at single-cell resolution during seed germination. The cellular domains of hormone sensitivity were explored within the Arabidopsis (Arabidopsis thaliana) embryo by putting seeds under GAlimiting conditions and quantifying cellular growth responses. The middle and upper hypocotyl have a greater requirement for GA to promote cell expansion than the lower embryo axis. Under these conditions, germination was still completed following enhanced growth within the radicle and lower axis. Under GA-limiting conditions, the athb5 mutant did not show a phenotype at the level of seed germination, but it did at a cellular level with reduced cell expansion in the hypocotyl relative to the wild type. These data reveal that the spatiotemporal cell expansion events driving this transition are not determinate, and the conditional use of GA-ATHB5-mediated hypocotyl growth under optimal conditions may be used to optionally support rapid seedling growth. This study demonstrates that multiple genetic and spatiotemporal cell expansion mechanisms underlie the seed to seedling transition in Arabidopsis.

Temperature variability is integrated by a spatially embedded decision-making center to break dormancy in Arabidopsis seeds

“…The lines used in this study are listed in SI Appendix, Supplementary Table 1. GUS activity was quantified using the fluorometric assays described by Stamm et al (46).…”

Temporal tissue‐specific regulation of transcriptomes during barley (Hordeum vulgare) seed germination

“…Cell expansion and division also occur under tight spatial regulation (Dekkers et al , ; Zhang et al , ; Topham et al , ; Narsai et al , ; Narsai et al , ). These processes require that specific genes are expressed in specific subsets of cells, under the control of distinct genome regulatory programs (Stamm et al , ; Topham et al , ). Transcription factors have an important role in regulating gene expression spatially and temporally during germination (Bassel et al , ; Narsai et al , ; Sánchez‐Montesino et al , ).…”

Regulation of Seed Germination: The Involvement of Multiple Forces Exerted via Gibberellic Acid Signaling

“…The importance of mechanical force adjustments by expansion of endosperm cells surrounding the elongating embryo prior to radicle emergence as critical for successful germination has been identified in Arabidopsis thaliana (Bassel et al, 2014;Sá nchez-Montesino et al, 2018;Stamm et al, 2017). Using cell surface area measurements by confocal imaging and 3D geometry reconstruction, Sá nchez-Montesino et al (2018) identified that the region of the endosperm surrounding the lower hypocotyl and the radicle exhibit the highest expansion rates in imbibed seeds.…”