The Arabidopsis Phosphatidylinositol 3-Kinase Is Important for Pollen Development    

Abstract

Phosphatidylinositol 3-kinase has been reported to be important for normal plant growth. To characterize the role of the enzyme further, we attempted to isolate Arabidopsis (Arabidopsis thaliana) plants that do not express the gene, but we could not recover homozygous mutant plants. The progeny of VPS34/vps34 heterozygous plants, harboring a T-DNA insertion, showed a segregation ratio of 1:1:0 for wild-type, heterozygous, and homozygous mutant plants, indicating a gametophytic defect. Genetic transmission analysis showed that the abnormal segregation ratio was due to failure to transmit the mutant allele through the male gametophyte. Microscopic observation revealed that 2-fold higher proportions of pollen grains in heterozygous plants than wild-type plants were dead or showed reduced numbers of nuclei. Many mature pollen grains from the heterozygous plants contained large vacuoles even until the mature pollen stage, whereas pollen from wild-type plants contained many small vacuoles beginning from the vacuolated pollen stage, which indicated that vacuoles in many of the heterozygous mutant pollen did not undergo normal fission after the first mitotic division. Taken together, our results suggest that phosphatidylinositol 3-kinase is essential for vacuole reorganization and nuclear division during pollen development.

A BAR-Domain Protein SH3P2, Which Binds to Phosphatidylinositol 3-Phosphate and ATG8, Regulates Autophagosome Formation in Arabidopsis

“…On the other hand, it is possible that SH3P2 has roles beyond autophagy. As the PI3K complex has been implicated in regulating both pollen germination and root hair growth in plants (Lee et al, 2008a(Lee et al, , 2008bPatel and DineshKumar, 2008), we indeed found that root hair growth is also impaired when SH3P2 is downregulated ( Figure 7C). Future works should examine whether the lethality of the sh3p2 mutant is due to its essential roles during autophagy or its involvement in other pathway(s).…”

Plant phospholipid signaling: “in a nutshell”

“…Silencing AtVPS43 causes severe defects in development, while knockout mutants are lethal, indicating an important function (43)(44)(45). About 5-15% of the PtdInsP pool in plants is PtdIns3P, with the majority (?80%) being PtdIns4P and containing a few percent of PtdIns5P (46).…”

An Autophagy-Related Kinase Is Essential for the Symbiotic Relationship between Phaseolus vulgaris and Both Rhizobia and Arbuscular Mycorrhizal Fungi

“…In Arabidopsis, PI3K is an essential gene that is expressed in almost all tissues, including pollen and root hairs (Welters et al, 1994;Lee et al, 2008aLee et al, , 2008b. In the roots of 2-d-old P. vulgaris seedlings, the relative accumulation of PI3K transcript was higher (5.4-fold) in the root hairs, the site of rhizobial entry into the root, and in the root apex (4.1-fold) than in the stripped root (depleted of root hairs) ( Figure 1A).…”

“…PI3P biosynthesis is catalyzed by PI3K, which is encoded by the only PI3K gene reported in Arabidopsis thaliana, Vacuolar protein sorting (Vps34). PI3P and PI3K/Vps34 are fundamental for normal plant growth and development (Welters et al, 1994;Liu et al, 2005;Lee et al, 2008aLee et al, , 2008b and have been implicated in various physiological functions, such as the innate immune response, intracellular trafficking, autophagy, senescence, and the symbiosis of legumes with rhizobia. In soybean (Glycine max), two isoforms of PI3K are differentially expressed in roots and nodules.…”