MicroRNA analysis reveals 2 modules that antagonistically regulate xylem tracheary element development in Arabidopsis.

Tracheary elements (TEs) are vital in the transport of various substances and contribute to plant growth. The differentiation of TEs is complex and regulated by a variety of microRNAs (miRNAs). However, the dynamic changes in miRNAs during each stage of TE differentiation remain unclear, and the miRNA regulatory network is not yet complete. This study employed Vascular cell Induction culture System Using Arabidopsis Leaves to profile the miRNome during TE differentiation in Arabidopsis (Arabidopsis thaliana) and established comprehensive miRNA co-expression networks functioning at the different stages of TE differentiation. Two negatively correlated modules exist in the miRNA networks, each exhibiting strong intra-module positive correlation and strong inter-module negative correlation. Thus, the 2 modules may play opposite roles in TE differentiation and vascular development. Indeed, we found that miR408 promotes cambium formation and TE differentiation, consistent with miR408 as a key node in the networks of fate determination and the initiation of TE differentiation. Additionally, we found that miR163 inhibits secondary cell wall formation and TE differentiation, corresponding to miR163 as a key node in the TE maturation network. Moreover, we discovered that the miRNA co-expression network in poplar (Populus tomentosa) xylem development is also composed of 2 negatively correlated modules that contain miRNAs orthologous to those in Arabidopsis. Therefore, the 2 negatively correlated modules of the miRNA co-expression network are likely conserved and fundamental to xylem TE differentiation. These results provide insights into microRNA regulation in plant development.