Sustained low abscisic acid levels increase seedling vigor under cold stress in rice (Oryza sativa L.).

Ryosuke Mega,Etsuo Shimosaka,Seiji Murayama,Ayano Meguro-Maoka,Eiji Nambara,Yutaka Sato,Akira Endo,Mitsunori Seo,Suzanne R Abrams,Yuri Kanno

doi:10.1038/srep13819

Abstract

Stress-induced abscisic acid (ABA) is mainly catabolized by ABA 8′-hydroxylase (ABA8ox), which also strictly regulates endogenous ABA levels. Although three members of the ABA8ox gene family are conserved in rice, it is not clear which stressors induce expression of these genes. Here, we found that OsABA8ox1 was induced by cold stress within 24 h and that OsABA8ox2 and OsABA8ox3 were not. In contrast, OsABA8ox2 and OsABA8ox3 were ABA-inducible, but OsABA8ox1 was not. OsABA8ox1, OsABA8ox2, and OsABA8ox3 restored germination of a cyp707a1/a2/a3 triple mutant of Arabidopsis to rates comparable to those of the wild type, indicating that OsABA8ox1, OsABA8ox2, and OsABA8ox3 function as ABA-catabolic genes in vivo. Transgenic rice lines overexpressing OsABA8ox1 showed decreased levels of ABA and increased seedling vigor at 15 °C. These results indicate that sustained low levels of ABA lead to increased seedling vigor during cold stress. On the other hand, excessively low endogenous ABA levels caused reduced drought and cold tolerance, although some of the transgenic rice lines expressing OsABA8ox1 at moderate levels did not show these harmful effects. Adequate regulation of endogenous ABA levels is thought to be crucial for maintaining seedling vigor under cold stress and for cold and drought tolerance in rice.

Highlights

Introduction ofOsABA8ox[1], OsABA8ox[2], or OsABA8ox[3] into cyp707a1/cyp707a2/cyp707a3 triple mutant of Arabidopsis
Because we found that OsABA8ox[1] was not induced at 15 °C and that ABA content increased at this temperature (Fig. 3B), we measured shoot growth, ABA content, and expression changes of OsABA8ox[1] and other ABA metabolic genes under long-term cold stress to confirm the effect of ABA accumulation
The differential inducibility among the OsABA8ox homologs may be unique to rice, because the Arabidopsis CYP707A1, CYP707A2, CYP707A3, and CYP707A4 genes are all induced by ABA, drought, high salinity, and osmotic stress[17]

Summary

Introduction

OsABA8ox[1], OsABA8ox[2], or OsABA8ox[3] into cyp707a1/cyp707a2/cyp707a3 triple mutant of Arabidopsis. OsABA8ox[1], OsABA8ox[2], or OsABA8ox[3] cDNA fragments were amplified by PCR from synthesized total cDNA with the following primers: OsABA8ox[1], ABA8ox1_ fw and ABA8ox1_rv; OsABA8ox[2], ABA8ox2_fw and ABA8ox2_rv; OsABA8ox[3], ABA8ox3_fw and ABA8ox3_rv (Supplementary Table SI). These fragments were cloned into pENTR/D-TOPO vectors (Life Technologies, Rockville).

Methods

Results

Discussion

Conclusion