Novel expression patterns of phosphatidylinositol 3-hydroxy kinase in nodulated Medicago spp. plants

A cDNA clone encoding a phosphatidylinositol 3-kinase (PtdIns 3-kinase) has been characterized from Medicago truncatula, Mtpi3k, that is highly homologous to their counterparts from soybean (over 84%). The results suggest the presence of at least two genes coding PtdIns 3-kinases in M. truncatula. Mtpi3k transcript levels increased in nodules, compared with non-infected roots. Strikingly, Mtpi3k mRNA accumulated in young elongating stems at higher levels than that observed in other organs. Enhanced transcription of genes coding PtdIns 3-kinases might occur in tissues experiencing a high degree of vesicle trafficking and cell elongation

Regulation of the pollen-specific actin-depolymerizing factor LIADF1

Pollen tube growth is dependent on a dynamic actin cytoskeleton, suggesting that actin-regulating proteins are involved. We have examined the regulation of the lily pollen-specific actin-depolymerizing factor (ADF) LlADF1. Its actin binding and depolymerizing activity is pH sensitive, inhibited by certain phosphoinositides, but not controlled by phosphorylation. Compared with its F-actin binding properties, its low activity in depolymerization assays has been used to explain why pollen ADF decorates F-actin in pollen grains. This low activity is incompatible with a role in increasing actin dynamics necessary to promote pollen tube growth. We have identified a plant homolog of actin-interacting protein, AIP1, which enhances the depolymerization of F-actin in the presence of LlADF1 by 60%. Both pollen ADF and pollen AIP1 bind F-actin in pollen grains but are mainly cytoplasmic in pollen tubes. Our results suggest that together these proteins remodel actin filaments as pollen grains enter and exit dormancy

Changes in starch and inositol 1,4,5-trisphosphate levels and auxin transport are interrelated in graviresponding oat ( Avena sativa ) shoots

This study was conducted to unravel a mechanism for the gravitropic curvature response in oat ( Avena sativa ) shoot pulvini. For this purpose, we examined the downward movement of starch-filled chloroplast gravisensors, differential changes in inositol 1,4,5-trisphosphate (IP 3 ) levels, transport of indole-3-acetic acid (IAA) and gravitropic curvature. Upon gravistimulation, the ratio for IAA levels in lower halves versus those in upper halves (L/U) increased from 1.0 at 0 h and reached a maximum value of 1.45 at 8 h. When shoots were grown in the dark for 10 d, to deplete starch in the chloroplast, the gravity-induced L/U of IAA was reduced to 1.0. N -naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both auxin transport inhibitors, significantly reduced the amount of gravitropic curvature and gravity-induced lateral IAA transport, but did not reduce the gravity-induced late change in the L/U ratio of IP 3 levels. U73122, a specific phospholipase C (PLC) inhibitor, decreased gravity-induced curvature. Because U73122 reduced the ratio of L/U of IAA imposed by gravistimulation, it is clear that IAA transport is correlated with changes in IP 3 levels upon gravistimulation. These results indicate that gravistimulation-induced differential lateral IAA transport may result from the onset of graviperception in the chloroplast gravisensors coupled with gravity-induced asymmetric changes in IP 3 levels in oat shoot pulvini.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74234/1/j.1365-3040.2006.01584.x.pd