Cytokinins are a class of essential plant hormones regulating plant growth and development. Although the two-component phosphorelay pathway of cytokinin has been well characterized, the intact cytokinin responses regu...Cytokinins are a class of essential plant hormones regulating plant growth and development. Although the two-component phosphorelay pathway of cytokinin has been well characterized, the intact cytokinin responses regulation picture still needs to be fully depicted. Here we report a new mutant, long life span I （llsl）, which displays dwarf stature, curled leaves, numerous axillary branches and nearly 5-month life span. Exogenous cytokinin could not recover the phenotypes of the mutant. Moreover, mutation in Ilsl suppressed the cytokinin-responsive phenotypes, including root and hypocotyl growth inhibition, anthocyanin accumulation, metaxylem promotion in primary root development. The induction of cytokinin-responsive genes, ARR5, AHP5, and CKX3, was also suppressed in llsl. According to quantitative RT-PCR （qRT-PCR） and microarray results, the basal expression of positive factors AHP5, ARR1, and ARRIO were down-regulated, while the negative factors ARR4 and ARR5 were up-regulated. Our results suggested that LLS1 gene might be involved in the regulation of cytokinin signaling. It was mapped to chromosome 4 where no other cytokinin relevant gene has been reported.展开更多
Cytokinin is a critical growth regulator for various aspects of plant growth and development. In Arabidopsis, cytokinin signaling is mediated by a two-component system-based phosphorelay that transmits a signal from t...Cytokinin is a critical growth regulator for various aspects of plant growth and development. In Arabidopsis, cytokinin signaling is mediated by a two-component system-based phosphorelay that transmits a signal from the receptors, through histidine phosphotransfer proteins, to the downstream response regulators （ARRs）. Of these ARRs, type-A ARR genes, whose transcription can be rapidly induced by cytokinin, act as negative regulators of eytokinin signaling. However, because of functional redundancy, the function of type-A ARR genes in plant growth and development is not well understood by analyzing loss-of-function mutants. In this study, we performed a comparative functional study on all ten type-A ARR genes by analyzing transgenic plants overexpressing these ARR genes fused to a MYC epitope tag. Overexpression of ARR genes results in a variety of cytokinin-associated phenotypes. Notably, overexpression of different ARR transgenes causes diverse phenotypes, even between phylogenetically closely-related gene pairs, such as within the ARR3-ARR4 and ARR5-ARR6 pairs. We found that the accumulation of a subset of ARR proteins （ARR3, ARR5, ARR7, ARR16 and ARR17; possibly ARR8 and ARR15） is increased by MG132, a specific proteasomal inhibitor, indicating that stability of these proteins is regulated by proteasomal degradation. Moreover, similar to that of previously characterized ARR5, ARR6 and ARR7, stability of ARR16 and ARR17, possibly including ARR8 and ARR15, is regulated by cytokinin. These results suggest that type-A ARR proteins are regulated by a combinatorial mechanism involving both the cytokinin and proteasome pathways, thereby executing distinctive functions in plant growth and development.展开更多
基金supported by the National Science Foundation Program (No.30771155)
文摘Cytokinins are a class of essential plant hormones regulating plant growth and development. Although the two-component phosphorelay pathway of cytokinin has been well characterized, the intact cytokinin responses regulation picture still needs to be fully depicted. Here we report a new mutant, long life span I （llsl）, which displays dwarf stature, curled leaves, numerous axillary branches and nearly 5-month life span. Exogenous cytokinin could not recover the phenotypes of the mutant. Moreover, mutation in Ilsl suppressed the cytokinin-responsive phenotypes, including root and hypocotyl growth inhibition, anthocyanin accumulation, metaxylem promotion in primary root development. The induction of cytokinin-responsive genes, ARR5, AHP5, and CKX3, was also suppressed in llsl. According to quantitative RT-PCR （qRT-PCR） and microarray results, the basal expression of positive factors AHP5, ARR1, and ARRIO were down-regulated, while the negative factors ARR4 and ARR5 were up-regulated. Our results suggested that LLS1 gene might be involved in the regulation of cytokinin signaling. It was mapped to chromosome 4 where no other cytokinin relevant gene has been reported.
文摘Cytokinin is a critical growth regulator for various aspects of plant growth and development. In Arabidopsis, cytokinin signaling is mediated by a two-component system-based phosphorelay that transmits a signal from the receptors, through histidine phosphotransfer proteins, to the downstream response regulators （ARRs）. Of these ARRs, type-A ARR genes, whose transcription can be rapidly induced by cytokinin, act as negative regulators of eytokinin signaling. However, because of functional redundancy, the function of type-A ARR genes in plant growth and development is not well understood by analyzing loss-of-function mutants. In this study, we performed a comparative functional study on all ten type-A ARR genes by analyzing transgenic plants overexpressing these ARR genes fused to a MYC epitope tag. Overexpression of ARR genes results in a variety of cytokinin-associated phenotypes. Notably, overexpression of different ARR transgenes causes diverse phenotypes, even between phylogenetically closely-related gene pairs, such as within the ARR3-ARR4 and ARR5-ARR6 pairs. We found that the accumulation of a subset of ARR proteins （ARR3, ARR5, ARR7, ARR16 and ARR17; possibly ARR8 and ARR15） is increased by MG132, a specific proteasomal inhibitor, indicating that stability of these proteins is regulated by proteasomal degradation. Moreover, similar to that of previously characterized ARR5, ARR6 and ARR7, stability of ARR16 and ARR17, possibly including ARR8 and ARR15, is regulated by cytokinin. These results suggest that type-A ARR proteins are regulated by a combinatorial mechanism involving both the cytokinin and proteasome pathways, thereby executing distinctive functions in plant growth and development.
