The movement of a leaf-derived mobile AGL24 mRNA specifies floral organ identity in Arabidopsis

Cell-to-cell and inter-organ communication play pivotal roles in synchronizing and coordinating plant development. In addition to serving as templates for protein translation within cells, many mRNAs can move and exert their function non-cell-autonomously. However, because the proteins encoded by some mobile mRNAs are also mobile, whether the systemic function of mobile mRNAs is attributed to proteins transported distally or translated locally remains controversial. Here, we show that Arabidopsis AGAMOUS-LIKE 24 (AGL24) mRNA acts as a leaf-derived signal to specify meristem identity. AGL24 is expressed in both apex and leaves. Upon floral meristem (FM) transition, apex-expressed AGL24 is transcriptionally inhibited by APETALA1 (AP1) to ensure FM differentiation. The leaf-expressed AGL24 can act as a mobile signal to bypass AP1 inhibition and revert FM differentiation. Although AGL24 mRNA is expressed in leaves, AGL24 protein is rapidly degraded in leaves. In contrast, AGL24 mRNA can move long distance from leaf to apex where the translocated AGL24 mRNAs can be used as templates to translate into proteins. Thus, the movement of AGL24 mRNA can provide the developmental plasticity to fit with environmental dynamics.