Detecting the Different Responses of Roots and Shoots to Gravity in Salix matsudana (Koidz)

The study of the gravity response of roots and shoots is of great significance when exploring the polarity of plants and the development of the forest industry. In our study, normal and inverted cuts of Salix matsudana (Koidz) were cultured. The total RNAs of roots and shoots were extracted. Based on the comparative transcriptome, 412 and 668 genes were differentially expressed. The plasma membrane-, cell wall-, and extracellular region-related genes were up-regulated in the shoots, while the carbon metabolism and the nitrogen metabolism were up-regulated in the roots. Combining the alternative splicing genes, we found a potential gravity response network: in the shoots, LecRLKs were highly sensitive to gravity and further affected the alternative splicing of SNARE, as well as inducing an inhomogeneous distribution of auxin and a negative geotropism curve. In the roots, AP2/ERFs and STRKs were highly sensitive to gravity and regulated the expression level of STPKs and WAKs, finally resulting in a geotropism curve. Moreover, cell division was suppressed in both the roots and the shoots under inverted conditions with different mechanisms. Cell division inhibitors (KRPs) were up-regulated in the roots, while DNA helicase MCMs were down-regulated in the shoots. These results provide an important foundation for further studies of the molecular mechanisms and genetic regulation of plant responses to gravity and the plant polarity of forest trees.