Abstract
BackgroundSeedlessness is an important agronomic trait for citrus, and male sterility (MS) is one main cause of seedless citrus fruit. However, the molecular mechanism of citrus seedlessness remained not well explored.ResultsAn integrative strategy combining suppression subtractive hybridization (SSH) library with cDNA microarray was employed to study the underlying mechanism of seedlessness of a Ponkan mandarin seedless mutant (Citrus reticulata Blanco). Screening with custom microarray, a total of 279 differentially expressed clones were identified, and 133 unigenes (43 contigs and 90 singletons) were obtained after sequencing. Gene Ontology (GO) distribution based on biological process suggested that the majority of differential genes are involved in metabolic process and respond to stimulus and regulation of biology process; based on molecular function they function as DNA/RNA binding or have catalytic activity and oxidoreductase activity. A gene encoding male sterility-like protein was highly up-regulated in the seedless mutant compared with the wild type, while several transcription factors (TFs) such as AP2/EREBP, MYB, WRKY, NAC and C2C2-GATA zinc-finger domain TFs were down-regulated.ConclusionOur research highlighted some candidate pathways that participated in the citrus male gametophyte development and could be beneficial for seedless citrus breeding in the future.
Highlights
Seedlessness is an important agronomic trait for citrus, and male sterility (MS) is one main cause of seedless citrus fruit
Phenotype analysis of the floral organs of QS Previous studies suggested that the floral organs of QS had no morphological difference from the wild type
To further validate the phenotype of this seedless Ponkan mandarin, we measured the length of filament and pistil, and the average ratio of filament to pistil was 0.83 ± 0.01 for Egan NO.1’ (EG) and 0.79 ± 0.01 for QS
Summary
Seedlessness is an important agronomic trait for citrus, and male sterility (MS) is one main cause of seedless citrus fruit. In most flowering plants, seed initiation requires signals activated by the double fertilization event that occurs in the embryo sac, and seed is produced sexually from the fertilized ovule [2,3] Various phytohormones such as gibberellins (GAs), auxins and cytokinins are involved in this signaling process [4,5,6]. Ectopic expression of iaaH gene with DefH9 as promoter to elevate auxin levels in placenta or ovules resulted in seedless fruits [19,20]. Another effective strategy was by specific expression of toxin proteins during early development of plant reproductive organs. The Arabidopsis thaliana MAC12.2 gene had been introduced into precocious trifoliate orange (Poncirus trifoliata [L.] Raf) for production of potential seedless fruits [25]
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