A Brassica napus Reductase Gene Dissected by Associative Transcriptomics Enhances Plant Adaption to Freezing Stress.

Muhammad Azhar Hussain,Yan Lv,Xuekun Zhang,Hongzhi Xu,Chuan Zeng,Yong Huang,Yong Cheng,Lenka Havlickova,Guangyuan Lu,Ian Bancroft,Dan Luo,Xiling Zou,Zhitao Tian

doi:10.3389/fpls.2020.00971

Abstract

Cold treatment (vernalization) is required for winter crops such as rapeseed (Brassica napus L.). However, excessive exposure to low temperature (LT) in winter is also a stress for the semi-winter, early-flowering rapeseed varieties widely cultivated in China. Photosynthetic efficiency is one of the key determinants, and thus a good indicator for LT tolerance in plants. So far, the genetic basis underlying photosynthetic efficiency is poorly understood in rapeseed. Here the current study used Associative Transcriptomics to identify genetic loci controlling photosynthetic gas exchange parameters in a diversity panel comprising 123 accessions. A total of 201 significant Single Nucleotide Polymorphisms (SNPs) and 147 Gene Expression Markers (GEMs) were detected, leading to the identification of 22 candidate genes. Of these, Cab026133.1, an ortholog of the Arabidopsis gene AT2G29300.2 encoding a tropinone reductase (BnTR1), was further confirmed to be closely linked to transpiration rate. Ectopic expressing BnTR1 in Arabidopsis plants significantly increased the transpiration rate and enhanced LT tolerance under freezing conditions. Also, a much higher level of alkaloids content was observed in the transgenic Arabidopsis plants, which could help protect against LT stress. Together, the current study showed that AT is an effective approach for dissecting LT tolerance trait in rapeseed and that BnTR1 is a good target gene for the genetic improvement of LT tolerance in plant.

Highlights

Rapeseed (Brassica napus L.) is one of the major oil crops worldwide, with an average annual cropping area of 35.3 million hectares producing 72.8 million tons of seeds in the past five years
Gsw was the most variable trait since it has the largest coefficient of variation (0.69), with a minimum of 0.16 and a maximum of 2.53 mol (H2O) m−2 s−1; the range of broad-sense heritability varied from 49.49% to 68.91% (Supplementary Table S4)
The genetic architecture of photosynthetic gas exchange parameters was investigated by Associative transcriptomics (AT) approach, and a gene termed BnTR1 was confirmed to be responsible for E trait (Figure 4), which might be a promising candidate beneficial to rapeseed in coping with climatic changes

Summary

Introduction

Rapeseed (Brassica napus L.) is one of the major oil crops worldwide, with an average annual cropping area of 35.3 million hectares producing 72.8 million tons of seeds in the past five years (http://www.fao.org/faostat/). The semi-winter type rapeseed grown in China only needs moderate or weak vernalization, and excessive exposure to low temperature (LT) stress in winter will lead to plant damage at vegetative stage and cause yield loss (Liao and Guan, 2001; Zhang et al, 2015; O’neill et al, 2019). The rapeseed is usually sown in early October shortly after the harvest of rice in this area (Cong et al, 2019). In recent years, the delay of rice harvest usually lead to the postpone of rapeseed sowing until late October or early November, which results in poor germination and seedling establishment due to LT (Luo et al, 2019). To cope with LT stresses, plants have evolved several elaborate regulatory mechanisms; among these, balancing or coordinating the photosynthetic processes could be a critical one (Leister, 2019)

Methods

Results

Discussion

Conclusion