Variations in physiological response and expression profiles of proline metabolism-related genes and heat shock transcription factor genes in petunia subjected to heat stress

Abstract

High temperature is a critical constraint factor limiting plant growth and productivity of crops throughout the world. Petunia (Petunia hybrida) is a well-known ornamental plant which is widely grown in gardens. However, petunia does not tolerate high temperatures well and seedling production and landscape uses are seriously inhibited in the summer. In this study, a total of ten physiological indexes were selected to analyze the physiological responses of petunia ‘W115’ under heat stress. Partial least squares-discriminant analysis showed that the physiological responses of petunia ‘W115’ to heat stress could be classified into three critical time points (0.5 h, 3 h, and 72 h after stress), and that proline concentration was the most important core physiological index to reflect the heat-stress response of petunia seedlings. In order to elucidate the molecular regulatory mechanism of heat-stress response in petunia ‘W115’, the expression patterns of eight proline metabolism pathway genes and of 12 heat shock transcription factors (Hsfs) were studied by real-time quantitative PCR under heat stress. Expression analysis indicated that the expression trend of the proline synthetase gene (PhP5CR) was most closely correlated with the change in proline concentration, and the expression levels of most Hsfs were markedly up-regulated, especially PhHsf19 and PhHsf21, which were highly expressed during the entire heat-stress period, suggesting that these genes could play important roles in response to heat stress in petunia ‘W115’. We hope this research could deepen our understanding of the heat-stress response mechanism of petunia ‘W115’ seedlings and identify candidate genes for molecular breeding for heat tolerance in the future.