The function of AMP1 in shoot meristem development

The aerial structure of higher plants is generated through the activity of stem cells which are located at the tip of the stem, in the shoot apical meristem (SAM). Continous cell division in the SAM produces stem tissue and lateral organs, and simultaniousely guarantees the maintanance of the stem cell pool. To ensure correct growth, the plant must tightly balance the ratio between pluripotent stem cells and differentiating cells, which are consumed by organ formation. This requires constant intercellular communication and is achieved by complex interactions of numerous signalling molecules. The plant hormone cytokinin, identified due to its absolute requirement for plant cell division and de novo shoot organogenesis, has long been associated with SAM function and recent findings revealed that classical meristem identity factors act through the modulation of cytokinin biosynthesis or signalling in the meristem. The Arabidopsis amp1 mutant is unique in combining strong enlargement of SAM size with a drastic increase in cytokinin levels, further indicating a close link between cytokinin and SAM function. However how these phenotypes in amp1 are functionally related is currently not known. AMP1 encodes a glutamate carboxypeptidase like protein. Based on its molecular identity the primary function of AMP1 has been proposed to be the control of an unknown peptide signal that restricts SAM size and that the elevated cytokinin levels in amp1 are a consequence of deregulation of meristem proliferation. The proposed work is intended to test this hypothesis by using a complementary set of approaches and should further unravel how AMP1 interacts with known developmental regulators of meristem activity. The project also includes a careful analysis of AMP1 tissue distribution as well as its subcellular localisation. Moreover a genetic screen for downstream components required for AMP1 activity will be conducted to extend our knowledge about the molecular network in which AMP1 exerts its control on meristem function.

The aerial structure of higher plants is generated through the activity of stem cells which are located at the tip of the stem, in the shoot apical meristem (SAM). Continous cell division in the SAM produces stem tissue and lateral organs, and simultaniousely guarantees the maintanance of the stem cell pool. To ensure correct growth, the plant must tightly balance the ratio between pluripotent stem cells and differentiating cells, which are consumed by organ formation. This requires constant intercellular communication and is achieved by complex interactions of numerous signalling molecules. The plant hormone cytokinin, identified due to its absolute requirement for plant cell division and de novo shoot organogenesis, has long been associated with SAM function and recent findings revealed that classical meristem identity factors act through the modulation of cytokinin biosynthesis or signalling in the meristem. The Arabidopsis amp1 mutant is unique in combining strong enlargement of SAM size with a drastic increase in cytokinin levels, further indicating a close link between cytokinin and SAM function. However how these phenotypes in amp1 are functionally related is currently not known. AMP1 encodes a glutamate carboxypeptidase like protein. Based on its molecular identity the primary function of AMP1 has been proposed to be the control of an unknown peptide signal that restricts SAM size and that the elevated cytokinin levels in amp1 are a consequence of deregulation of meristem proliferation. The proposed work is intended to test this hypothesis by using a complementary set of approaches and should further unravel how AMP1 interacts with known developmental regulators of meristem activity. The project also includes a careful analysis of AMP1 tissue distribution as well as its subcellular localisation. Moreover a genetic screen for downstream components required for AMP1 activity will be conducted to extend our knowledge about the molecular network in which AMP1 exerts its control on meristem function.