Two Novel Mitogen-Activated Protein Signaling Components, OsMEK1 and OsMAP1, Are Involved in a Moderate Low-Temperature Signaling Pathway in Rice

Abstract

Rice (Oryza sativa) anther development is easily damaged by moderately low temperatures above 12°C. Subtractive screening of cDNA that accumulated in 12°C-treated anthers identified a cDNA clone, OsMEK1, encoding a protein with features characteristic of a mitogen-activated protein (MAP) kinase kinase. The putative OsMEK1 protein shows 92% identity to the maize (Zea mays) MEK homolog, ZmMEK1. OsMEK1 transcript levels were induced in rice anthers by 12°C treatment for 48 h. Similar OsMEK1 induction was observed in shoots and roots of seedlings that were treated at 12°C for up to 24 h. It is interesting that no induction of OsMEK1 transcripts was observed in 4°C-treated seedlings. In contrast, rice lip19, encoding a bZIP protein possibly involved in low temperature signal transduction, was not induced by 12°C treatment but was induced by 4°C treatment. Among the three MAP kinase homologs cloned, only OsMAP1 displayed similar 12°C-specific induction pattern as OsMEK1. A yeast two-hybrid system revealed that OsMEK1 interacts with OsMAP1, but not with OsMAP2 and OsMAP3, suggesting that OsMEK1 and OsMAP1 probably function in the same signaling pathway. An in-gel assay of protein kinase activity revealed that a protein kinase (approximately 43 kD), which preferentially uses myelin basic protein as a substrate, was activated by 12°C treatment but not by 4°C treatment. Taken together, these results lead us to conclude that at least two signaling pathways for low temperature stress exist in rice, and that a MAP kinase pathway with OsMEK1 and OsMAP1 components is possibly involved in the signaling for the higher range low-temperature stress.Rice (Oryza sativa) is widely cultivated in a large number of different natural environments (Nishiyama, 1984). Compared with other cereal crops such as wheat (Triticum aestivum) and barley (Hordeum vulgare), rice is much more sensitive to low temperature as a result of its tropical origin. Male sterility is the most severe consequence among the many chilling-induced agronomic damages in rice production. The developmental stages from pollen formation to fertilization are the most vulnerable to low temperature throughout the life cycle of rice plants (Nishiyama, 1984). It has been reported that the young microspore stage in pollen development was the most sensitive to low temperature (Satake and Hayase, 1970). Exposure of rice plants at the tetrad stage to a moderately low temperature (12°C) for 4 d resulted in male sterility in 80% of spikelets (Satake and Hayase, 1970; Nishiyama, 1984). Microscopic observation of developing rice anthers suggested that one possible reason for the male sterility after lowtemperature treatment was the failure of anther development. The observed abnormalities included the cessation of anther development, the arrest of pollen development, anthers remaining within the flowers after anthesis, and partial or no dehiscence (Satake, 1976). Cytological observation revealed a dilatation of tapetal layers in chilling-treated rice anthers (Nishiyama, 1976(Nishiyama,...

MAPK cascades and major abiotic stresses

“…In the same way, OsMEK1 (a putative rice MAP kinase kinase, isolated by subtractive screening of cDNA library) has been shown to interact with OsMAP1 at 12°C, suggesting that both kinases, OsMEK1 and OsMAP1, may be involved in the temperature stress signaling (Wen et al 2002). Another MAP kinase, called OsMAPK4, has also been identified in rice leaves and roots with strong upregulation by cold stress (Fu et al 2002).…”

Toward Understanding Molecular Mechanisms of Abiotic Stress Responses in Rice

“…Expression analysis reveals that MAPKKK OsEDR1, an ortholog of Arabidopsis AtEDR1, is probably associated with development and the defense/stress response [81]. The expression pattern of MAPK kinase OsMEK1 is similar to that of OsMAP1 under abiotic stress [178]. Both OsMEK1 and OsMAP1 messenger RNA levels are induced by treatment at a moderately low temperature (12°C) but not at 4°C.…”

“…Two-hybrid analysis reveals that OsMEK1 interacts with OsMAP1. The OsMEK1-OsMAP1 pathway, therefore, may be involved in moderately low-temperature signaling in rice [178].…”

“…Salt, cold, and sugar starvation induce the expression of OsMAPK4, which is differentially expressed at different development stages [35]. A MAPK gene, OsMAP1 (also named OsMAPK5, OsMSRMK2, OsMAPK2, and OsBIMK1), is induced by multiple biotic and abiotic stresses such as pathogen infection, low temperature, salinity, drought, and ABA [4,61,159,178,182]. OsMAP1 can inversely modulate abiotic stress tolerance and broad-spectrum disease resistance.…”

Genome-wide transcriptome modulation in rice transgenic lines expressing engineered mitogen activated protein kinase kinase 6

“…OsMKK6 (earlier named as OsMEK1) specifically and physically interacted with OsMPK3 (earlier named as OsMAP1) in moderate low temperature stress signaling as shown by yeast two hybrid assay. 9 Transcript studies have revealed that OsMKK4 and OsMKK6 are strongly regulated by salt and cold stress.…”