CHOTTO1, a Putative Double APETALA2 Repeat Transcription Factor, Is Involved in Abscisic Acid-Mediated Repression of Gibberellin Biosynthesis during Seed Germination in Arabidopsis

Ryoichi Yano,Yuji Kamiya,Yuri Kanno,Kazumi Nakabayashi,Eiji Nambara,Yusuke Jikumaru

doi:10.1104/pp.109.142018

Abstract

The phytohormones abscisic acid (ABA) and gibberellins (GAs) are the primary signals that regulate seed dormancy and germination. In this study, we investigated the role of a double APETALA2 repeat transcription factor, CHOTTO1 (CHO1), in seed dormancy, germination, and phytohormone metabolism of Arabidopsis (Arabidopsis thaliana). Wild-type seeds were dormant when freshly harvested seeds were sown, and these seeds were released from dormancy after a particular period of dry storage (after-ripening). The cho1 mutant seeds germinated easily even in a shorter period of storage than wild-type seeds. The cho1 mutants showed reduced responsiveness to ABA, whereas transgenic plants constitutively expressing CHO1 (p35SCHO1) showed an opposite phenotype. Notably, after-ripening reduced the ABA responsiveness of the wild type, cho1 mutants, and p35SCHO1 lines. Hormone profiling demonstrated that after-ripening treatment decreased the levels of ABA and salicylic acid and increased GA(4), jasmonic acid, and isopentenyl adenine when wild-type seeds were imbibed. Expression analysis showed that the transcript levels of genes for ABA and GA metabolism were altered in the wild type by after-ripening. Hormone profiling and expression analyses indicate that cho1 seeds, with a short period of storage, resembled fully after-ripened wild-type seeds. Genetic analysis showed that the cho1 mutation partially restored delayed seed germination and reduced GA biosynthesis activity in the ABA-overaccumulating cyp707a2-1 mutant background but did not restore seed germination in the GA-deficient ga1-3 mutant background. These results indicate that CHO1 acts downstream of ABA to repress GA biosynthesis during seed germination.

Highlights

The phytohormones abscisic acid (ABA) and gibberellins (GAs) are the primary signals that regulate seed dormancy and germination
Our results indicated that (1) afterripening affects the levels of ABA but aNl6s-o(DG2-Ais4o, pjaesnmteonnyilc)aadceidnin(JeA()i,Ps)aalficteyrliicmabciibdit(iSoAn )i,natnhde wild type; (2) after-ripening affects the transcript levels of genes involved in ABA and GA metabolism beyond seed dormancy release in the wild type; and (3) the pattern of phytohormone levels and transcript levels indicate that shortly stored cho1 mutant seeds mimic fully after-ripened wild-type seeds
To investigate the effect of cho1 mutations on seed dormancy and germination, germination of wild-type and cho1 seeds was compared after a variable period of dry storage

Summary

Introduction

The phytohormones abscisic acid (ABA) and gibberellins (GAs) are the primary signals that regulate seed dormancy and germination. The after-ripening treatment reduces seed dormancy and increases the germination potential by enhancing the sensitivity of seeds to factors that promote germination, like light and GA, and decreasing the sensitivity to those inhibiting germination (Derkx and Karssen, 1993; Bewley, 1997; Ali-Rachedi et al, 2004; Finch-Savage and Leubner-Metzger, 2006). In this sense, most of previous studies on seed germination have used after-ripened seeds as experimental tools. It has been shown that after-ripening affects the expression of a large number of genes, even in the nondormant mutants

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Results

Conclusion