molecular dissection of the crop maturation trait in peanut

Crop maturation is one of the most recognized characteristics of peanut, and it is crucial for adaptability and yield. However, not much is known regarding its genetic and molecular control. The goals of this project were to study the molecular-genetic components that control crop maturation in peanut and identify candidate genes. Crop maturation was studied directly by phenotyping the maturity level or through other component traits such as flowering pattern and branching habit. Six different RIL populations (HH, RR, CC, FNC, TGT and FLIC) were used for the genetic analysis. In total, 14 QTLs were found for maturity level. The phenotypic explanation values ranged in 5.3%-18.6%. Common QTL were found between maturity level and harvest index (in RR and CC populations), branching habit (in HH population), flowering pattern/branching rate (in CC and TGT populations) and pod size (in CC population). Further investigations were done to define genes that control maturity level and the component traits. A map-based cloning approach was used to identify a major candidate gene for branching habit - a novel AhMADS-box gene (AhMADS). AhMADS was mainly expressed in the lateral shoot, the organ in which the difference between branching habit occurs. Sequence alignment analysis found SNPs in AhMADS that cause to exon/intron splicing alterations. Overexpression study of AhMADs-box in tobacco under 35S control revealed one line with a spreading-like lateral shoot indicating that AhMADS may be the causing effect of BH and therefore indirectly controls maturity level. In addition, several candidate genes were defined that may control flowering pattern. An RNA expression study was performed on two parental lines, Tifrunner and GT-C20, identifying four candidate genes in the flowering regulatory pathway that were down-regulated at the mainstem (non-flowering) compared to the first (flowering) shoot, indicating their influence on flowering pattern. Also, another candidate gene was identified, Terminal Flowering 1-like (AhTFL1), which was located within a small segment in chromosome B02. A 1492 bp deletion was found in AhTFL1 that completely co-segregates with the flowering pattern phenotype in the CC population and two independent EMS-mutagenized M2 families. AhTFL1 was significantly less expressed in flowering than non-flowering branches. Finally, a field trial showed that an EMS line (B78) mutagenized in AhTFL1 is ~18% days earlier than the control (Hanoch). In conclusion, our study revealed new insights into the molecular basis for the fundamentally important crop maturity trait in peanut. The results generated new information and materials that will promote informed targeting of peanut idiotypes by indirect selection and genomic breeding approaches.