Cytosolic fructose-1,6-bisphosphatase isoform mediates metabolic adjustments in bean fruit pericarp to support seed growth.

Abstract

Seed development requires substantial metabolic resources and is influenced by adverse environmental conditions. However, the ability of plants to produce viable seeds under restrictive conditions suggests the existence of mechanisms that make this process less sensitive to environmental stress. Uncovering their regulation could lead to the development of genotypes better adapted to stressful conditions. Plant response to stress is complex, and the contribution of organs such as the fruit pericarp to stress tolerance mechanism may have been underestimated. The bean fruit pericarp, a photosynthetic structure that contributes to seed development, can synthesize starch from surplus sucrose, which is later degraded during the rapid seed growth phase. This metabolic flexibility may be crucial for supporting seed growth when the photosynthate supply is reduced. To explore this possibility, we disrupted phloem continuity at the pedicel level in fruits about to enter the seed reserve accumulation stage. We used the capacity of the pericarp to incorporate ¹⁴CO₂ to investigate changes in its metabolism. Our findings reveal that, in response to reduced photosynthate availability, the fruit pericarp did not increase ¹⁴CO₂ fixation. However, the amount of ¹⁴C used for starch synthesis decreased, while the proportion used for soluble sugars synthesis increased. This shift resulted in an increase in ¹⁴C-products transported to seeds was accompanied by a significant increase in the activity of cytosolic fructose 1,6-bisphosphatase. Our results indicate that photosynthate restriction accelerates the degradation of pericarp storage proteins, and the increase in cFBPase activity could be crucial in converting the carbon produced in carbohydrates.