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Abstract
High temperature stress results in yield loss and alterations to seed composition during seed filling in oilseed rape (Brassica napus). However, the mechanism underlying this heat response is poorly understood. In this study, global transcription profiles of 20 d-old siliques of B. napus were analyzed after heat stress using a Brassica 95k EST microarray. The up-regulated genes included many HSF/HSP transcripts and other heat-related marker genes, such as ROF2, DREB2a, MBF1c and Hsa32, reflecting the conservation of key heat resistance factors among plants. Other up-regulated genes were preferentially expressed in heat-stressed silique walls or seeds, including some transcription factors and potential developmental regulators. In contrast, down-regulated genes differed between the silique wall and seeds and were largely tied to the biological functions of each tissue, such as glucosinolate metabolism in the silique wall and flavonoid synthesis in seeds. Additionally, a large proportion (one-third) of these differentially expressed genes had unknown functions. Based on these gene expression profiles, Arabidopsis mutants for eight heat-induced Brassica homologous genes were treated with different heat stress methods, and thermotolerance varied with each mutation, heat stress regimen and plant development stage. At least two of the eight mutants exhibited sensitivity to the heat treatments, suggesting the importance of the respective genes in responding to heat stress. In summary, this study elucidated the molecular bases of the heat responses in siliques during later reproductive stages and provides valuable information and gene resources for the genetic improvement of heat tolerance in oilseed rape breeding.
Highlights
High temperature is a major abiotic stress that severely restricts crop production [1]
Overview of gene expression affected by heat stress in B. napus siliques at the seed-filling stage
To identify genes responsive to heat stress in oilseed rape at the seed-filling stage, a Brassica 95k EST microarray was used to profile the transcripts from both the silique wall (SW) and seeds separated from 20 days after flowering (DAF) siliques
Summary
High temperature is a major abiotic stress that severely restricts crop production [1]. During the period from bolting to the end of flowering, a threshold temperature of 29.5uC resulted in seed yield loss in three different Brassica species: B. napus, B. rapa and B. juncea [9]. When a heat stress of 35/18uC (day/night) was applied to three B. juncea cultivars and one B. napus cultivar for 10 d at three distinct reproductive stages, the seed yield per plant was reduced by 77% at the pod development stage, 58% at the flowering stage and 15% at the bud formation stage [13]. A very high temperature stress of 38/23uC (day/night) applied for 5 d from 25 to 29 DAF moderately affected fatty acid composition by decreasing the oil content and reduced the seed yield by 52% on main stems, due to the reduction of seed weight [14]. We used functional genomic tools in Arabidopsis to identify novel genes involved in the heat response
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