ArabidopsisRAP2.2: An Ethylene Response Transcription Factor That Is Important for Hypoxia Survival    

Abstract

Arabidopsis (Arabidopsis thaliana) RAP2.2 (At3g14230) is an APETALA2/ethylene response factor-type transcription factor that belongs to the same subfamily as the rice (Oryza sativa) submergence tolerance gene SUB1A. RAP2.2 is expressed at constitutively high levels in the roots and at lower levels in the shoots, where it is induced by darkness. Effector studies and analysis of ethylene signal transduction mutants indicate that RAP2.2 is induced in shoots by ethylene and functions in an ethylene-controlled signal transduction pathway. Overexpression of RAP2.2 resulted in improved plant survival under hypoxia (low-oxygen) stress, whereas lines containing T-DNA knockouts of the gene had poorer survival rates than the wild type. This indicates that RAP2.2 is important in a plant's ability to resist hypoxia stress. Observation of the expression pattern of 32 low-oxygen and ethylene-associated genes showed that RAP2.2 affects only part of the low-oxygen response, particularly the induction of genes encoding sugar metabolism and fermentation pathway enzymes, as well as ethylene biosynthesis genes. Our results provide a new insight on the regulation of gene expression under low-oxygen conditions. Lighting plays an important regulatory role and is intertwined with hypoxia conditions; both stimuli may act collaboratively to regulate the hypoxic response.

Nitrogen metabolism in plants under low oxygen stress

“…AlaAT was induced under various oxygen stresses and that is probably why AlaAT was the only nitrogen metabolism gene described among the 49-core hypoxiaresponsive genes expressed in various tissues of 7-day old Arabidopsis plantlets grown on solid medium and gassed for 2 h by argon (99.99 %) (Mustroph et al 2009). AlaAT expression was similarly induced in Agrobacterium rhizogenes-induced hairy roots soaked in hypoxic (0.5 % O 2 ) liquid medium (Klok et al 2002), in young seedlings soaked in hypoxic (3 % O 2 ) (Liu et al 2005a) or anoxic (90 % N 2 -10 % H 2 ) (Loreti et al 2005) liquid medium and in plantlets grown on solid medium under anoxic (99.99 % argon), or hypoxic (1 or 1.5 % O 2 ) atmosphere (van Dongen et al 2009;Hinz et al 2010). Other nitrogen metabolism genes, without being ubiquitously overexpressed under low oxygen stress, were more or less up-regulated in specific studies, e.g., glutamate dehydrogenase (GDH2; At5g07440), glutamate decarboxylase (GDC1; At5g17330) and glutamate synthase (NADH-GOGAT; At5g53460).…”

“…It is important to note that the expression of these genes under aerobic condition was as high as that in wild type under anaerobic condition (Gibbs et al 2011). In Arabidopsis seedlings, overexpressing RAP2.2 (Hinz et al 2010) or its closest homolog RAP2.12 (Licausi et al 2011) anaerobic carbon metabolism genes were strongly induced during low oxygen stress; changes in gene expression were accompanied by improved survival of the seedlings to flooding-induced low oxygen stress. Microarray analysis followed by quantitative RT-PCR for the comparison of genes induction by hypoxia treatment in wild type and Arabidopsis silenced in both RAP2.2 and RAP2.12 showed a reduced induction of anaerobic carbon metabolism genes in miRNA lines and confirmed that these transcription factors are required for the regulation of hypoxia-induced genes (Licausi et al 2011;Hinz et al 2010).…”

“…RAP2.2 is also constitutively expressed with high expression in the roots and weak expression in the shoots where it is induced by darkness (Hinz et al 2010). ACC and ethephon treatments as well as studies on ethylene signal transduction mutants showed that RAP2.2 is induced by ethylene and functions in an ethylene-controlled signal transduction pathway (Hinz et al 2010).…”

“…RAP2.2 is also constitutively expressed with high expression in the roots and weak expression in the shoots where it is induced by darkness (Hinz et al 2010). ACC and ethephon treatments as well as studies on ethylene signal transduction mutants showed that RAP2.2 is induced by ethylene and functions in an ethylene-controlled signal transduction pathway (Hinz et al 2010). HRE1 and HRE2 were shown to be hypoxia inducible genes , however, while HRE2 was insensitive to ethylene, HRE1 was induced by ethylene (Hess et al 2011) or by ACC (Yang et al 2011) under aerobic condition and showed hyper-induction when ACC treatment was combined to hypoxia (Yang et al 2011).…”

“…In Arabidopsis seedlings, overexpressing RAP2.2 (Hinz et al 2010) or its closest homolog RAP2.12 (Licausi et al 2011) anaerobic carbon metabolism genes were strongly induced during low oxygen stress; changes in gene expression were accompanied by improved survival of the seedlings to flooding-induced low oxygen stress. Microarray analysis followed by quantitative RT-PCR for the comparison of genes induction by hypoxia treatment in wild type and Arabidopsis silenced in both RAP2.2 and RAP2.12 showed a reduced induction of anaerobic carbon metabolism genes in miRNA lines and confirmed that these transcription factors are required for the regulation of hypoxia-induced genes (Licausi et al 2011;Hinz et al 2010). Interestingly, the overexpression of RAP2.2 and RAP2.12 did not affect the expression of hypoxia-induced genes when seedlings were grown under aerobic condition indicating that additional mechanisms interfere with the 1 3 signaling pathway controlled by these transcription factors.…”