Genome-Wide Identification and Analysis of the Ascorbate Peroxidase (APX) Gene Family of Winter Rapeseed (Brassica rapa L.) Under Abiotic Stress.

Li Ma,Weiliang Qi,Lijun Liu,Junyan Wu,Haiyun Li,Yuanyuan Pu,Wangtian Wang,Jing Bai,Yan Fang,Xuecai Li,Yaozhao Xu,Wancang Sun,Xiucun Zeng,Jia Xu

doi:10.3389/fgene.2021.753624

Li Ma, Weiliang Qi + Show 12 more

Open Access

https://doi.org/10.3389/fgene.2021.753624

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Abstract

Winter Brassica rapa (B. rapa) is an important oilseed crop in northern China, but the mechanism of its cold resistance remains unclear. Ascorbate peroxidase (APX) plays important roles in the response of this plant to abiotic stress and in scavenging free radicals. In this study, the roles of APX proteins in the cold response and superoxide metabolism pathways in rapeseed species were investigated, and a comprehensive analysis of phylogeny, chromosome distribution, motif identification, sequence structure, gene duplication, and RNA-seq expression profiles in the APX gene family was conducted. Most BrAPX genes were specifically expressed under cold stress and behaved significantly differently in cold-tolerant and weakly cold-resistant varieties. Quantitative real-time-PCR (qRT-PCR) was also used to verify the differences in expression between these two varieties under cold, freezing, drought and heat stress. The expression of five BrAPX genes was significantly upregulated in growth cones at 3 h of cold stress, while their expression was significantly lower at 24 h than at 3 h. The expression of Bra015403 and Bra003918 was significantly higher in “Longyou-7” growth cones than in other treatments. Five BrAPXs (Bra035235, Bra003918, Bra033040, Bra017120, and Bra031934) were closely associated with abiotic stress responses in B. rapa. These candidate genes may play important roles in the response of B. rapa to low temperature stress and provide new information for the elucidation of the cold resistance mechanism in B. rapa.

Highlights

Brassica rapa (B. rapa) (2n 20, AA) comprises several subspecies that provide human nutrition in the form of leafy, root and stem vegetables and edible oils
Ascorbate peroxidase gene in Brassica rapa (BrAPX) amino acid residue lengths ranged from 250 aa (Bra030706) to 723 aa (Bra011683), isoelectric point values ranged from 4.40 (Bra036445) to 10.78 (Bra019132), and molecular weights ranged from 27.39 kDa (Bra017830) to 80.97 kDa (Bra011683) (Supplementary Table S2)
We mapped the chromosomal locations of the Ascorbate peroxidase (APX) genes in B. rapa (Figure 1), with most genes located on Chr01 (16 genes), Chr02 (18 genes), Chr03 (18 genes), and Chr09 (15 genes), followed by chromosome Chr10 (12 genes) and Chr04, Chr05, Chr06, Chr07 and Chr08 with seven, six, nine, 10 and seven genes, respectively

Summary

Introduction

Brassica rapa (B. rapa) (2n 20, AA) comprises several subspecies that provide human nutrition in the form of leafy, root and stem vegetables and edible oils. In most regions in China north of 35° north latitude, extreme winter temperatures are below −20°C, cumulative negative air temperature is less than −500°C·a, and winter rainfall is below 30 mm (Sun et al, 2016; Ma et al, 2019b). Unfavourable factors such as severe cold and dry winters in northern China, which make it difficult for crops other than winter wheat to overwinter (Cai and Jiang, 2011). The breeding and production of B. rapa varieties have solved the problem of overwintering for oilseed crops and made northern cold and dry regions an important winter rapeseed production region in China, thereby increasing cropping intensity and economic return

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