Type B @entity1076 5-kinases mediate XXXX and @entity286 pollen tube growth by regulating apical pectin secretion.

@entity71105 @entity286 @entity17418 @entity1078 @entity958 @entity71104 @entity1076
@entity1078 [ @entity17418 ] occurs in the apical plasma membrane of growing pollen tubes. Because enzymes responsible for @entity17418 production at that location are uncharacterized, functions of @entity17418 in pollen tube tip growth are unresolved. Two candidate genes encoding pollen-expressed @entity958 @entity1076 5-kinases (PI4P 5-kinases) of @entity958 subfamily B were identified ( @entity71104 and @entity71105 ), and their recombinant proteins were characterized as being PI4P 5-kinases. Pollen of T-DNA insertion lines deficient in both @entity71104 and @entity71105 exhibited reduced pollen germination and defects in pollen tube elongation. Fluorescence-tagged @entity71104 and @entity71105 localized to an apical plasma membrane microdomain in @entity958 and @entity286 ( @entity286 ) pollen tubes, and overexpression of either @entity71104 or @entity71105 triggered multiple tip branching events. Further studies using the @entity286 system revealed that overexpression caused massive apical pectin deposition accompanied by plasma membrane invaginations. By contrast, callose deposition and cytoskeletal structures were unaltered in the overexpressors. Morphological effects depended on @entity17418 production, as an inactive enzyme variant did not produce any effects. The data indicate that excessive @entity17418 production by type B PI4P 5-kinases disturbs the balance of membrane trafficking and apical pectin deposition. Polar tip growth of pollen tubes may thus be modulated by @entity17418 via regulatory effects on membrane trafficking and/or apical pectin deposition.
