Abiotic Stress Responsive Rice ASR1 and ASR3 Exhibit Different Tissue-Dependent Sugar and Hormone-Sensitivities

Abstract

The expression of the six rice ASR genes is differentially regulated in a tissue-dependent manner according to environmental conditions and reproductive stages. OsASR1 and OsASR3 are the most abundant and are found in most tissues; they are enriched in the leaves and roots, respectively. Coexpression analysis of OsASR1 and OsASR3 and a comparison of the cis-acting elements upstream of OsASR1 and OsASR3 suggested that their expression is regulated in common by abiotic stresses but differently regulated by hormone and sugar signals. The results of quantitative real-time PCR analyses of OsASR1 and OsASR3 expression under various conditions further support this model. The expression of both OsASR1 and OsASR3 was induced by drought stress, which is a major regulator of the expression of all ASR genes in rice. In contrast, ABA is not a common regulator of the expression of these genes. OsASR1 transcription was highly induced by ABA, whereas OsASR3 transcription was strongly induced by GA. In addition, OsASR1 and OsASR3 expression was significantly induced by sucrose and sucrose/glucose treatments, respectively. The induction of gene expression in response to these specific hormone and sugar signals was primarily observed in the major target tissues of these genes (i.e., OsASR1 in leaves and OsASR3 in roots). Our data also showed that the overexpression of either OsASR1 or OsASR3 in transgenic rice plants increased their tolerance to drought and cold stress. Taken together, our results revealed that the transcriptional control of different rice ASR genes exhibit different tissue-dependent sugar and hormone-sensitivities.

ASR1 transcription factor and its role in metabolism

“…The characteristics of the cis-acting elements present in the regulatory regions of OsAsr1 and OsAsr3 suggest that stress, sugar and hormones are the key regulators of the expression of these rice paralogs. 18 In the same line, P erez-D ıaz et al 46 found that OsAsr1, OsAsr2 and OsAsr3 regulatory regions have a motif of sugar repression, whereas all rice ASR paralogs (Asr1 to Asr6) have an element of sugar induction and gibberellin repression in their regulatory regions. These data suggest that other paralogs of ASR1 could be involved in sugar-hormone crosstalk as well.…”

“…Among others, this increase occurs in tobacco and tomato by osmotic and drought stress; 4,16,[20][21][22] in rice by drought, saline and osmotic stress; 10,23,24,25 and in plantain and banana by osmotic and biotic stress. 11,26,27 Only a few physiological studies with transgenic tomato, 28 tobacco, 22 maize, 29 and rice 18 plants have proved the involvement of ASR1 in stress tolerance.…”

“…45 Evidence of the involvement of Asr1 in sugar-hormone crosstalk has been also found in other species. For instance, Joo et al 18 demonstrated that Asr1 mRNA levels in rice leaves increased significantly after sucrose and ABA treatment, whereas Asr3 (an Asr1 paralog) mRNA levels in roots increased after sucrose, glucose and gibberellic acid treatment. The characteristics of the cis-acting elements present in the regulatory regions of OsAsr1 and OsAsr3 suggest that stress, sugar and hormones are the key regulators of the expression of these rice paralogs.…”

The MaASR gene as a crucial component in multiple drought stress response pathways in Arabidopsis

“…Several orthologous and paralogous ASR genes have been found to be transcriptionally regulated by ABA and sugar signaling (Amitai-Zeigersona et al 1995;Çakir et al 2003;Kalifa et al 2004;Liu et al 2010;Chen et al 2011;Henry et al 2011;Virlouvet et al 2011;Joo et al 2013). Additionally, overexpression of some ASR genes resulted in reduced sensitivity to ABA and changed transcription levels of ABA/ stress-responsive genes (Yang et al 2005;Shkolnik and BarZvi 2008).…”

Overexpression of the rice basic leucine zipper transcription factor OsbZIP12 confers drought tolerance to rice and makes seedlings hypersensitive to ABA

“…The plasmids were introduced into Agrobacterium tumefaciens LBA4404 through triparental mating, and embryogenic calli from mature rice seeds were transformed. The callus induction, co-cultivation with A. tumefaciens and selection of transformed calli were performed (Joo et al 2013).…”