Deciphering the genetic basis of chlorophyll fluorescence parameters and vegetation indices under heat stress in...

Blueberry (Vaccinium section Cyanococcus) is a commercially important fruit crop. Its cultivation is challenging due to specific climate and soil requirements, with even minor temperature fluctuations potentially affecting growth and fruit yield. Heat stress impairs growth and photosynthesis by causing damage to the photosystem II (PSII) complex. Hence, identifying genomic regions influencing the maximum quantum efficiency of PSII and the overall photosynthetic capacity of plants under heat stress is crucial.

In this study, we exposed 266 interspecific cross derivatives of blueberry plants to heat stress in controlled conditions for two consecutive years and evaluated their responses through phenotypic, chlorophyll fluorescence, and vegetation indices measurements. We observed continuous and significant variation for all the measured traits, indicating their quantitative nature. Genome-wide association studies (GWAS) using 126,816 single-nucleotide polymorphisms revealed several candidate genes encoding molecular chaperones, serine-threonine kinases, and DEAD-box proteins, which play critical roles in heat stress responses in plants. Additionally, we identified 10,393 differentially expressed genes (DEGs) from the transcriptomic analysis of V. corymbosum and V. darrowii plants subjected to 6 and 9 hours of heat stress. RNA-Seq data were further confirmed by quantitative real-time PCR analysis of randomly selected genes. Functional characterization through Gene Ontology and pathway analysis of 325 genes commonly expressed in all four comparison groups indicated that DEGs were mainly enriched in protein processing in the endoplasmic reticulum. Through GWAS and transcriptomic analysis, we uncovered 23 genes on chromosomes 1, 2, 3, 4, 5, 7, 8, 9, 10, and 12 associated with chlorophyll fluorescence parameters and vegetation indices under heat stress.

This study provides a deeper understanding of the genetic basis of chlorophyll fluorescence under heat stress in blueberries, offering valuable information for breeding strategies to develop blueberry cultivars with enhanced photosynthetic efficiency.