Comparative Transcriptome-Based Analysis of the Regulation of Leaf Senescence in the Upper and Middle Canopy of Different Soybean Cultivars

Abstract

Premature leaf failure is one of the major factors contributing to crop yield reduction. High-yielding soybean cultivars exhibit a longer leaf lifespan during the reproductive period, promoting higher yields. In this experiment, physiological indexes and transcriptomics analysis were carried out on leaves of different canopy parts of two soybean cultivars with different senescence sensitivities of LD32 and SND28 as test materials. The results showed that the leaf senescence rates of the two soybean cultivars, tested at the grain-filling stage, were significantly different, and the senescence rates of the upper and middle canopy leaves of LD32 were significantly lower than those of SND28. In comparison to SND28, LD32 exhibited slower decreases in chlorophyll, net photosynthetic rate, and SPAD values in the upper and middle canopy leaves. The differentially expressed genes for senescence of upper and middle canopy leaves of both cultivars were enriched in four pathways: the photosynthesis pathway, the photosynthesis–antenna protein pathway, the MAPK signaling pathway–plant hormone signal transduction pathway, and the plant hormone signal transduction pathway. The differential expression of 20 genes (Ribose-5-phosphate isomerase, fructose-1,6-bisphosphatase, etc.) in the “carbon fixation in photosynthetic organisms” pathway of LD32 may be involved in the regulation of reducing the rate of leaf senescence in the middle of the canopy at the grain-filling stage of LD32. Ribose-5-phosphate isomerase and fructose-1,6-bisphosphatase in LD32 may reduce the rate of leaf senescence in the middle of the canopy during seed filling.