Interaction Between AtCML9 and AtMLO10 Regulates Pollen Tube Development and Seed Setting.

Qian Zhang,Yudan Tian,Jiali Song,Xiaohan Wang,Changxin Feng,Tiange Li,Congcong Hou,Mengou Li,Wang Tian,Legong Li,Zhijie Ren,Jinlong Qiu,Mitianguo Tang,Liangyu Liu

doi:10.3389/fpls.2020.01119

Abstract

In higher-plant reproduction, the compatibility of pollen tube germination in the pistil is essential for successful double fertilization. It has been reported that Mildew Locus O (MLO) family gene NTA (MLO7), expressing in synergid cells, can correctly guide pollen tubes. However, the molecular mechanism underlying the interacting partners to MLOs in the fertilization is still unknown. In our study, we identified the direct protein interaction between CML9 and MLO10 within a non-canonical CaMBD. In GUS reporter assays, CML9 expresses in a high level in pollens, whereas MLO10 can be specifically detected in stigma which reaches up to a peaking level before fertilization. Therefore, the spatio-temporal expression patterns of MLO10 and CML9 are required for the time-window of pollination. When we observed the pollen germination in vitro, two cml9 mutant alleles dramatically reduced germination rate by 15% compared to wild-type. Consistently, the elongation rate of pollen tubes in planta was obviously slow while manually pollinating cml9-1 pollens to mlo10-1 stigmas. Additionally, cml9-1 mlo10-1 double mutant alleles had relatively lower rate of seed setting. Taken together, protein interaction between MLO10 and CML9 is supposed to affect pollen tube elongation and further affect seed development.

Highlights

Reproductive process is critical for flowering plants
We have identified the new protein interacting complex MLO10–CML9 which is involved in pollen germination, pollen tube elongation as well as seed setting
We focused on the possible interacting partners especially the calcium sensor proteins to MLO10 in Arabidopsis thaliana

Summary

Introduction

Reproductive process is critical for flowering plants. After physically attaching to the stigma epidermal, pollen grains successively adhere, hydrate, and germinate. Pollen tubes penetrating along the style are guided to the ovary to release the sperms (Zheng et al, 2018). Those steps require the matured male and female organs to communicate and recognize each other, and any molecule inhibiting male–female recognition leads to incompatibility. Pollen–stigma recognition usually depends on specific protein–protein interactions, which is classified into several types of compatibilities (Knox et al, 1976; Dumas and Knox, 1983).

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