Antagonistic pleiotropy of Ln gene controls trade-off between 2-seeded pods and 4-seeded pods in soybean

Ln locus in soybean ( Glycine max (L.) Merrill) is known to pleiotropically control leaf shape and number of seeds per pods (NSDPPD). Ln/Ln soybean(s) have broad leaflets and low NSDPPD, while ln/ln soybean(s) have narrow leaflets and high NSDPPD. Although the ln allele has potential to improve seed yield through increased NSDPPD (increased number of 4-seeded pods), previous studies demonstrated that the ln provides neither advantage nor disadvantage to seed yield. The reason behinds this phenomenon is not yet fully known. In this study, we investigated pleiotropic effect of the Ln gene on leaflet width (LFW), leaflet length (LFL), LFL/LFW ratio (L/W), leaflet area (LFA), N1SDPD (number of 1-seeded pods per plant), N2SDPD, N3SDPD, N4SDPD, NSDPPD, number of seeds per plant (NSDPP), number of pods per plant (NPDPPP), seed weight (100SDW), and seed yield per plant (SDYPP) by quantitative trait locus (QTL) analysis using recombinant inbred lines derived from the cross between Sukhothai 1 (narrow leaflet ( ln / ln )) and CM60-10KR-71-PS-21 (broad leaflet ( Ln / Ln )). QTL analysis showed that Ln is associated with LFW, LFL, L/W, LFA, N2SDPD, N4SDPD, NSDPPD, and 100SDW. The ln allele(s) increased, LFL, L/W, N3SDPD, N4SDPD, and NSDPPD, but decreased LFW, LFA, N2SDPD, and 100SDW. Nonetheless, the effect of ln allele(s) towards N3SDPD and 100SDW was not always detected. Correlation analysis confirmed negative relationship between N2SDPD and N4SDPD. Therefore, reducing in N2SDPD canceled effect of N4SDPD in enhancing seed yield in ln/ln soybean. Overall, these results indicate that the Ln gene pleiotropically and antagonistically regulates N2SDPD and N4SDPD, and thus the trade-off between these two traits.