在進化過程中，導管的出現是陸生高等植物成功的主要原因。導管的分化過程經歷了細胞伸長、細胞壁局部加厚和細胞程序化死亡3個階段。與真菌和動物不同，保守的exocyst分泌複合體的EXO70亞基在高等植物基因組中大量擴增。
中科院植物研究所劉春明組對在分化的導管細胞特異表達的EXO70A1進行了深入研究，發現該基因參與了擬南芥導管分化，通過控制囊泡的定向運輸決定導管細胞壁定點增厚。該研究對於了解高等植物維管束分化調控機理具有重要意義。(生物谷Bioon.com)
生物谷推薦英文摘要：
Plant Cell doi:10.1105/tpc.113.112144
EXO70A1-Mediated Vesicle Trafficking Is Critical for Tracheary Element Development in Arabidopsis
Exocysts are highly conserved octameric complexes that play an essential role in the tethering of Golgi-derived vesicles to target membranes in eukaryotic organisms. Genes encoding the EXO70 subunit are highly duplicated in plants. Based on expression analyses, we proposed previously that individual EXO70 members may provide the exocyst with functional specificity to regulate cell type– or cargo-specific exocytosis, although direct evidence is not available. Here, we show that, as a gene expressed primarily during tracheary element (TE) development, EXO70A1 regulates vesicle trafficking in TE differentiation in Arabidopsis thaliana. Mutations of EXO70A1 led to aberrant xylem development, producing dwarfed and nearly sterile plants with very low fertility, reduced cell expansion, and decreased water potential and hydraulic transport. Grafting of a mutant shoot onto wild-type rootstock rescued most of these aboveground phenotypes, while grafting of a wild-type shoot to the mutant rootstock did not rescue the short root hair phenotype, consistent with the role of TEs in hydraulic transport from roots to shoots. Histological analyses revealed an altered pattern of secondary cell wall thickening and accumulation of large membrane-bound compartments specifically in developing TEs of the mutant. We thus propose that EXO70A1 functions in vesicle trafficking in TEs to regulate patterned secondary cell wall thickening.