How do seeds get bigger? A newly identified phloem-terminal tissue controls seed enlargement through callose degradation

The fundamental and enigmatic question of why seeds enlarge after fertilization has yet to be definitively answered. A recent study provided one clue by revealing that the Arabidopsis thaliana β-1,3-glucanase-encoding gene AtBG_ppap regulates nutrient influx through the degradation of callose in the chalazal region of the ovule. The tissue that accumulated callose in the chalazal region was identified as the terminal end of the phloem and was found to function as a multifunctional gateway. Remarkably, this discovery marks the first time in 160 years that a new plant tissue has been identified.