Various tomato cultivars display contrasting morphological and molecular responses to a chronic heat stress
Climate change is one of the biggest threats that human society currently needs to face. Heat waves associated with global warming negatively affect plant growth and development and will increase in intensity and frequency in the coming years. Tomato is one of the most produced and consumed fruit in the world but remarkable yield losses occur every year due to the sensitivity of many cultivars to heat stress. New insights into how tomato plants are responding to heat stress will contribute to the development of cultivars with high yields under harsh temperature conditions. In this study, the analysis of microsporogenesis and pollen germination rate of eleven tomato cultivars after exposure to a chronic heat stress revealed differences between genotypes. The transcriptome of floral buds at two developmental stages of five cultivars revealed common and specific molecular responses implemented by tomato cultivars to cope with chronic heat stress. These data provide valuable insights into the diversity of the genetic response of floral buds from different cultivars to heat stress and may contribute to the development of future climate resilient tomato varieties. Overall design: To identify the molecular pathways differentially regulated in the floral buds of five  tomato cultivars (WVA106, DRK7024, M82, Monemaker, JAG8810) under HS, we carried out a genome-wide transcriptomic analysis by RNAseq on the five previously studied cultivars. RNA was extracted from floral buds of each tomato cultivar grown under NS or HS conditions (3 weeks at 35°C during the day (16h) and 25°C during the night (8h)). Based on the previous histological analysis, floral buds were harvested at the tetrad stage (tetrad floral bud, TFB) and at the pollen mature stage (pollen floral bud, PFB) based on their size,