Cultivar variation in hormone- and sugar-response reveals abscisic acidresponsive sucrose phloem loading at the early regenerative stage is a significant determinant of seed yield in Brassica napus

Abstract

Seed crop yield is determined by manipulating source-sink interaction. To characterize the metabolic and signaling network encompassing plant hormones and sugar, seed yield in two cultivars of Brassica napus was interpreted as being linked to changes in the physiological parameters involved in carbohydrate metabolism and endogenous hormone level from the bolting to pod filling stage. Overall salicylic acid (SA), jasmonic acid (JA), and gibberellic acid (GA) increased, whereas indole-3-acetic acid (IAA) and abscisic acid (ABA) decreased from the bolting to pod filling stage. In both cultivars Akela and Colosse, leaf senescence progressed as evidenced by the loss of photosynthetic pigment and enhanced expression of senescence-related gene SAG12. Leaf senescence parameters were shown to be closely associated with enhanced hexose/sucrose ratio, but not with sucrose. Sucrose content was largely higher at the bolting stage, then decreased significantly at the pod filling stage in an ABA-dependent manner. Sucrose content was parallel with the expression of ABA-responsive element binding 2 (AREB2) and sucrose non-fermenting kinase 2 (SnRK2). Sucrose phloem loading at the bolting stage was shown to be more influential in determining seed yield. In the higher seed yielding cultivar Colosse, the highest sucrose phloem loading with enhanced expression of SUT4 and SWEET11 was reflected in the highest expression of SnRK2 and AREB2 in an ABA-dependent manner. Thus, these results indicate that sucrose transport from mature leaves at the bolting stage, which is eventually regulated by ABA-responsive sucrose signaling genes SnRK2 and AREB2, is a significant determinant of seed yield of oilseed rape.