NtGNL1 Plays an Essential Role in Pollen Tube Tip Growth and Orientation Likely via Regulation of Post-Golgi Trafficking

Fanglei Liao,Lu Wang,Mengxiang Sun,Li-Bo Yang,Xiongbo Peng,Diane Bassham

doi:10.1371/journal.pone.0013401

Abstract

BackgroundTobacco GNOM LIKE 1 (NtGNL1), a new member of the Big/GBF family, is characterized by a sec 7 domain. Thus, we proposed that NtGNL1 may function in regulating pollen tube growth for vesicle trafficking.Methodology/Principal FindingsTo test this hypothesis, we used an RNAi technique to down-regulate NtGNL1 expression and found that pollen tube growth and orientation were clearly inhibited. Cytological observations revealed that both timing and behavior of endocytosis was disrupted, and endosome trafficking to prevacuolar compartments (PVC) or multivesicular bodies (MVB) was altered in pollen tube tips. Moreover, NtGNL1 seemed to partially overlap with Golgi bodies, but clearly colocalized with putative late endosome compartments. We also observed that in such pollen tubes, the Golgi apparatus disassembled and fused with the endoplasmic reticulum, indicating abnormal post-Golgi trafficking. During this process, actin organization was also remodeled.Conclusions/SignificanceThus, we revealed that NtGNL1 is essential for pollen tube growth and orientation and it likely functions via stabilizing the structure of the Golgi apparatus and ensuring post-Golgi trafficking.

Highlights

During fertilization in higher plants, pollen landing on the receptive stigma of the pistil germinates, producing a pollen tube that grows and carries male gametes to the embryo sac for final gamete fusion [1]
To test whether abnormalities of pollen tube growth relate to vesicle trafficking, we compared the uptake process of FM4-64 in RNAi and normal samples to observe the dynamics of vesicle trafficking
The endosome distribution pattern was obviously disturbed in these pollen tubes after the inhibition of NtGNL1expression. These results further demonstrate that NtGNL1 is involved in regulating endosome trafficking, which is essential for normal pollen tube growth and orientation

Summary

Introduction

During fertilization in higher plants, pollen landing on the receptive stigma of the pistil germinates, producing a pollen tube that grows and carries male gametes to the embryo sac for final gamete fusion [1]. Two basic processes take place during pollen tube growth, tube extension and orientation, which ensure that the pollen tube reaches the correct destination. The pollen tube extends via tip growth, during which polarized apical secretion results in unidirectional cell expansion [2]. This provides an excellent example of polarized growth and an ideal model system for clarifying the processes of organization and regulation [3], attracting broad interest for several decades [4,5,6]. We proposed that NtGNL1 may function in regulating pollen tube growth for vesicle trafficking

Methods

Results

Conclusion