ASHS 2024 Conference

Pecan (Carya illinoinensis), a North American native nut crop, exhibits two distinct flowering habits where male and female flowering occur at separate times. Trees that shed pollen before their pistillate flowers become receptive are classified as protandrous or type 1 (recessive homozygous, pp), while those with pistillate flowers receptive before pollen shed are protogynous or type 2 (dominant heterozygous, PP/Pp). Establishing commercial pecan orchards requires planting both types of pecan cultivars to ensure optimal pollination for maximum production. To investigate critical genes associated with pecan heterodichogamous flowering, we collected tissues from four stages (dormant buds, swollen buds, immature catkins, and immature pistils) of three genotypes (PP, Pp, and pp). Paired-end RNA sequencing at 125/150 bp read lengths was conducted on an Illumina platform. Clean and unique reads were mapped to an annotated 'Pawnee’ reference genome. Out of 32,267 annotated genes, over 5,000 (~15%) were identified to have alternative splicing events associated with pecan flowering dichogamy. We illustrate by three genes that present significant alternative splicing patterns associated with dichogamy genotypes, distinguishing the pp genotype from PP and Pp genotypes. These genes exhibited 6-18 nucleotide differences in RNA sequence between the pp genotype and PP/Pp genotypes, potentially resulting in an altered protein product with 2-6 amino acid differences between type 1 and type 2 genotypes. This study provides evidence for the prevalence of alternative RNA splicing in the transcription regulation of pecan dichogamy.