Seed-Specific Expression of Apolipoprotein A-IMilano Dimer in Engineered Rice Lines

Apolipoprotein A-IMilano(ApoA-IM)has been shown to significantly reduce coronary atherosclerotic plaques.However,the preparation of cost-effective pharmaceutical formulations of ApoA-IM is limited by the high cost and difficulty of purifying the protein and producing the highly effective dimeric form.The aim of this study was to create an expression cassette that specifically drives the expression of dimeric ApoA-IM in the protein bodies of rice seeds.The ApoA-IM protein under control of the 13 kDa prolamin promoter is expressed exclusively in its dimeric form within the seeds,and immunocytochemical and immunogold analyses confirmed its expression in different caryopsis tissue such as seed coat,aleurone cell and endosperm,particularly in amyloplast and storage vacuoles.A plant-based ApoA-IM production system offered numerous advantages over current production systems,including the direct production of the most therapeutically effective dimeric ApoA-IM forms,long-term protein storage in seeds,and ease of protein production by simply growing plants.Therefore,seeds had the potential to serve as a costeffective source of therapeutic ApoA-IM.

Pollen Tube Growth: a Delicate Equilibrium Between Secretory and Endocytic Pathways

Although pollen tube growth is a prerequisite for higher plant fertilization and seed production, the processes leading to pollen tube emission and elongation are crucial for understanding the basic mechanisms of tip growth. It was generally accepted that pollen tube elongation occurs by accumulation and fusion of Golgi-derived secretory vesicles （SVs） in the apical region, or clear zone, where they were thought to fuse with a restricted area of the apical plasma membrane （PM）, defining the apical growth domain. Fusion of SVs at the tip reverses outside cell wall material and provides new segments of PM. However, electron microscopy studies have clearly shown that the PM incorporated at the tip greatly exceeds elongation and a mechanism of PM retrieval was already postulated in the mid-nineteenth century. Recent studies on endocytosis during pollen tube growth showed that different endocytic pathways occurred in distinct zones of the tube, including the apex, and led to a new hypothesis to explain vesicle accumulation at the tip; namely, that endocytic vesicles contribute substantially to V-shaped vesicle accumulation in addition to SVs and that exocytosis does not involve the entire apical domain. New insights suggested the intriguing hypothesis that modulation between exo- and endocytosis in the apex contributes to maintain PM polarity in terms of lipid/protein composition and showed distinct degradation pathways that could have different functions in the physiology of the cell. Pollen tube growth in vivo is closely regulated by interaction with style molecules. The study of endocytosis and membrane recycling in pollen tubes opens new perspectives to studying pollen tube-style interactions in vivo.

Microtubule Depolymerization Affects Endocytosis and Exocytosis in the Tip and Influences Endosome Movement in Tobacco Pollen Tubes

Polarized organization of the cytoplasm of growing pollen tubes is maintained by coordinated function of actin filaments （AFs） and microtubules （MTs）. AFs convey post-Golgi secretory vesicles to the tip where some fuse with specific domains of the plasma membrane （PM）. Secretory activity is balanced by PM retrieval that maintains cell mem- brane economy and regulates the polarized composition of the PM, by dividing lipids/proteins between the shank and the tip. Although AFs play a key role in PM internalization in the shank, the role of MTs in exo-endocytosis needs to be characterized. The present results show that integrity of the MT cytoskeleton is necessary to control exo-endocytosis events in the tip. MT polymerization plays a role in promoting PM invagination in the apex of tobacco pollen tubes since nocodazole affected PM internalization in the tip and subsequent migration of endocytic vesicles from the apex for degradation. MT depolymerization in the apex and shank was associated with misallocation of a significantly greater amount of internalized PM to the Golgi apparatus and its early recycling to the secretory pathway. Fluorescence Recovery After Photobleaching （FRAP） experiments also showed that MT depolymerization in the tip region influenced the rate of exocytosis in the central domain of the apical PM.