Conserved LBL1-ta-siRNA and miR165/166-RLD1/2 modules regulate root development in maize.

Root system architecture and anatomy of monocotyledonous maize is significantly different from dicotyledonous model Arabidopsis. The molecular role of non-coding RNA (ncRNA) is poorly understood in maize root development. Here we address the role of LEAFBLADELESS1 (LBL1), a component of maize trans-acting short-interfering RNA (ta-siRNA), in maize root development. We report that the root growth, anatomical patterning, number of lateral roots (LRs) and monocot-specific crown roots (CRs) and seminal roots (SRs) are significantly affected in lbl1-rgd1 mutant, which is defective in production of ta-siRNA, including tasiR-ARF that targets AUXIN RESPONSE FACTOR3 (ARF3) in maize. Altered accumulation and distribution of auxin, due to differential expression of auxin biosynthesis and transporter genes, created an imbalance in auxin signaling. Altered expression of microRNA165/166 (miR165/166) and its targets ROLLED1/2 (RLD1/2) contributed to the changes in lbl1-rgd1 root growth and vascular patterning, as was evident by altered root phenotype of Rld1-O semi-dominant mutant. Thus, LBL1/ta-siRNA module regulates root development, possibly by affecting auxin distribution and signaling, in crosstalk with miR165/166-RLD1/2 module. We further showed that ZmLBL1 and its Arabidopsis homolog AtSGS3 proteins are functionally conserved.