Two Brassica napus cultivars differ in gene expression, but not in their response to submergence

Abstract

Heavy rainfall causes flooding of natural ecosystems as well as farmland, negatively affecting plant performance. While the responses of the wild model organism Arabidopsis thaliana to such stress conditions is well understood, little is known about the responses of its relative, the important oil crop plant Brassica napus. For the first time, we analyzed the molecular response of Brassica napus seedlings to full submergence in a natural light–dark cycle. We used two cultivars in this study, a European hybrid cultivar and an Asian flood‐tolerant cultivar. Despite their genomic differences, those genotypes showed no major differences in their responses to submergence. The molecular responses to submergence included the induction of defense‐ and hormone‐related pathways and the repression of biosynthetic processes. Furthermore, RNAseq revealed a strong carbohydrate‐starvation response under submergence in daylight, which corresponded with a fast depletion of sugars. Consequently, both B. napus cultivars exhibited a strong growth repression under water, but there was no indication of a low‐oxygen response. The ability of the European hybrid cultivar to form a short‐lived leaf gas film neither increased underwater net photosynthesis, underwater dark respiration nor growth during submergence. Due to the high sensitivity of both cultivars, the analysis of other cultivars or related species with higher submergence tolerance is required in order to improve flood tolerance of this crop species. One major target could be the improvement of underwater photosynthesis efficiency in order to enhance submergence survival.

Transcriptional Response of Two Brassica napus Cultivars to Short-Term Hypoxia in the Root Zone

“…Reads from the cultivar Zhongshuang 9 had a mapping rate of 67 to 75% (Supplementary Table 1). Mapping rates for leaves were generally higher than for roots and were similar to the mapping rates in our previous study (Wittig et al, 2021). DEG analysis was carried out with the edgeR and limma Bioconductor packages in R (McCarthy et al, 2012) as previously described (Müller et al, 2021).…”

“…The aim of our work was to (1) compare the transcriptional responses of two different Brassica napus cultivars to one aspect of waterlogging, hypoxic conditions in the root zone, including the analysis of roots and leaves at two different time points and (2) to evaluate with different growth conditions whether a difference in waterlogging tolerance exists between the two cultivars. In our previous analysis utilizing the same two cultivars (Wittig et al, 2021), we could not identify significant differences in submergence tolerance, but a strong transcriptional response to submergence in leaves of both genotypes. Here, we also identified a large number of transcripts induced by hypoxia in roots, which were mainly similar between the cultivars and also similar to the transcriptional response of Arabidopsis thaliana to hypoxia (Mustroph et al, 2009(Mustroph et al, , 2010Lee and Bailey-Serres, 2019).…”

“…Seeds of two rapeseed cultivars were used, the hybrid winter cultivar Avatar (Wollmer et al, 2018;Wittig et al, 2021) as well as the semi-winter cultivar Zhongshuang 9 (Zou et al, 2013a;Wittig et al, 2021).…”

“…The frozen tissue was ground in liquid nitrogen. RNA extraction, quality control, processing of the RNA for sequencing, and the subsequent bioinformatics analyses were carried out exactly as previously described (Wittig et al, 2021). Briefly, RNA was extracted by use of the ISOLATE II RNA plant kit (Bioline, Luckenwalde, Germany).…”

“…Previously we have shown that submerged leaves of Brassica napus showed a strong starvation response (Wittig et al, 2021). We therefore compared the present dataset to the starvation-responsive genes of Arabidopsis (Usadel et al, 2008;Cookson et al, 2016).…”