ATHB2 is a negative regulator of germination in Arabidopsis thaliana seeds

Rocío Soledad Tognacca,Monica Carabelli,Ida Ruberti,Giorgio Morelli,Javier Francisco Botto

doi:10.1038/s41598-021-88874-5

Abstract

The germination timing of seeds is of the utmost adaptive importance for plant populations. Light is one of the best characterized factors promoting seed germination in several species. The germination is also finely regulated by changes in hormones levels, mainly those of gibberellin (GA) and abscisic acid (ABA). Here, we performed physiological, pharmacological, and molecular analyses to uncover the role of ATHB2, an HD-ZIP II transcription factor, in germination of Arabidopsis seeds. Our study demonstrated that ATHB2 is a negative regulator and sustains the expression of transcription factors to block germination promoted by light. Besides, we found that ATHB2 increases ABA sensitivity. Moreover, ABA and auxin content in athb2-2 mutant is higher than wild-type in dry seeds, but the differences disappeared during the imbibition in darkness and the first hours of exposition to light, respectively. Some ABA and light transcription factors are up-regulated by ATHB2, such as ABI5, ABI3, XERICO, SOMNUS and PIL5/PIF1. In opposition, PIN7, an auxin transport, is down-regulated. The role of ATHB2 as a repressor of germination induced by light affecting the gemination timing, could have differential effects on the establishment of seedlings altering the competitiveness between crops and weeds in the field.

Highlights

The germination timing of seeds is of the utmost adaptive importance for plant populations
We reanalyzed the data for the presence of transcription factor genes that might be involved in the regulation of seed germination; we found that the R light significantly affected the expression of 492 transcription factors genes (~ 8.50% of our transcriptome): 251 genes were up-regulated and 241 genes were down-regulated (Supplementary Fig. 1 and Supplementary Table 1)
These genes belong to different families of transcription factors such as Homeodomain-Leucine zipper (HD-ZIP), bHLH, MYB, WRKY and GRAS, among others, and are related to (a) light response: PIL1, PIL2, SPT and ATHB2; (b) abscisic acid (ABA) signaling: FUS3, ABI4 and ABI5; (c) GA signaling: SCL3 and RGL1; (d) circadian clock: PRR1, PRR3, PRR5, PRR7, PRR9, TOC1, LHY and CCA1 (Supplementary Table 1)

Summary

Introduction

The germination timing of seeds is of the utmost adaptive importance for plant populations. Environmental signals that regulate dormancy depth and its alleviation define the germination timing of a seed population and are of the outmost adaptive importance[1] Relevant environmental factors such as temperature, light, and nitrates regulate seed dormancy relief to promote seed germination[2]. It has been shown that ATHB20 is strongly expressed in the micropylar endosperm and in the root cap of embryo, acting as positive regulator of seed germination[20] Another member of this family, ATHB23, functions as a positive regulator of the R light-dependent seed germination and mediates cotyledon expansion[21]. We demonstrated that ATHB2 delays light-induced germination in Arabidopsis by sustaining the expression of regulatory genes that increases ABA sensitivity and altering hormonal contents in the seeds

Methods

Results

Conclusion