Identification and Comparative Analysis of Genes and MicroRNAs Involved in the Floral Transition of the Xinjiang Early-Flowering Walnut (Juglans regia L.)

Abstract

For tree crops, shortening the juvenile phase is a vital strategy to advance fruit bearing and enhance the breeding efficiency. Walnut (Juglans regia L.) seedlings usually take at least eight to 10 years to flower, but early-flowering (EF) types can flower one or two years after planting. In this study, RNA sequencing (RNA-Seq) and microRNA sequencing (miRNA-Seq) were used for a transcriptome-wide analysis of gene and miRNA expression in hybrids of the Xinjiang EF walnut variety ‘Xinwen 81’ and later-flowering (LF) walnut. Based on a high-quality chromosome-scale reference genome, a total of 3009 differentially expressed genes (DEGs) were identified, of which 933 were upregulated (accounting for 31%) and 2076 were downregulated (accounting for 69%). DEGs were functionally annotated, and the flowering-related genes FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), and LEAFY (LFY) showed remarkable upregulation in EF compared with in the LF walnut. In addition, miRNAs associated with floral transition were screened as candidates for flowering time regulation in the walnut. This work provides new insights into walnut floral transition, which may ultimately contribute to genetic improvement of the walnut.