Tapetal Expression of BnaC.MAGL8.a Causes Male Sterility in Arabidopsis.

Jie Gao,Jitao Zou,Bin Yi,Jinxing Tu,Jing Wen,Baolong Tao,Qun Li,Chaozhi Ma,Tingdong Fu,Jinxiong Shen,Qiang Li,Nan Wang

doi:10.3389/fpls.2019.00763

Abstract

Monoacylglycerol lipase (MAGL) hydrolyzes monoacylglycerol, producing free fatty acid and glycerol. Although this enzyme has been shown to play important roles in mammal, its potential function in plants remains poorly understood. In a survey of the MAGL genes in Brassica napus, we found tapetal expression of BnaC.MAGL8.a, a homolog of AtMAGL8, results in male sterility in Arabidopsis thaliana. Retarded tapetal PCD and defective pollen wall were observed in the transgenic plants. The tapetal cells became vacuolated at stage 9, and then degenerated at stage 11. Most microspores degenerated with the tapetal cells, and only few pollen grains with an irregular-shaped exine layer were produced in the transgenic plants. Transcriptome analysis identified 398 differentially expressed genes. Most of them are involved in pollen development and stress response. ABORTED MICROSPORES and its downstream pollen wall biosynthesis genes were down-regulated, but genes related with reactive oxygen species homeostasis and jasmonates signaling were up-regulated in the transgenic plants. These results suggest that expression of BnaC.MAGL8.a in tapetum invokes stress response and impairs pollen development. The apparent phenotypic similarity between atgpat1 mutant and BnA9::BnaC.MAGL8.a transgenic plants lead us to propose a role for monoacylglycerol (MAG) in pollen development in Arabidopsis. Our study provides insights on not only the biological function of plant MAGL genes but also the role of MAG in pollen development.

Highlights

In mammals, triacylglycerol (TAG) breakdown proceeds through sequential hydrolysis reactions catalyzed by adipose tissue triacylglycerol lipase, hormone sensitive lipase, and monoacylglycerol lipase (MAGL) (Labar et al, 2010)
To explore the MAGL gene family in Brassica napus, 47 genes were identified from the Darmor-bzh genome database (Chalhoub et al, 2014) based on the protein sequence similarity with 16 AtMAGLs (Supplementary Figure S1)
As we were unable to purify maltose binding protein (MBP):BnaA.MAGL10.a recombinant protein for enzyme assay, this study is focused on the BnA9::BnaC.MAGL8.a transgenic plants

Summary

Introduction

Triacylglycerol (TAG) breakdown proceeds through sequential hydrolysis reactions catalyzed by adipose tissue triacylglycerol lipase, hormone sensitive lipase, and monoacylglycerol lipase (MAGL) (Labar et al, 2010). In addition to participate in fat mobilization, MAGLs regulate the endocannabinoid signaling system by controlling the level of 2-arachidonoylglycerol, which is a key messenger of the endocannabinoid system (Labar et al, 2010). The first MAGL gene was cloned from mice (Karlsson et al, 1997), and many MAGL identifications followed from various species (Karlsson et al, 2001; Heier et al, 2010). MAGLs belong to the alpha/beta hydrolase superfamily, containing the GXSXG motif and the catalytic triad of Ser, Asp, and His. In Arabidopsis, a total of 16 putative MAGL genes were identified (Kim et al, 2016). MAG hydrolytic activity were measured with 11 recombinant proteins, among which, AtMAGL6

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