Periclinal Cell Division Mediated By SHR Relies On ROS Microenvironment In Arabidopsis Roots

Root is an important organ for the absorption of water and nutrients in plants.Root structure is closely related to its physiological functions.Previous anatomic analysis of Arabiopsis roots showed the root radial patterning is composed of vascular bundles,pericycle,endodermis,cortex and epidermis from the inside to the outside.Both endodermis and cortex are derived from the cell periclinal division in the initial cells in stem cell niche,which is regulated by SHORT-ROOT?SHR?.Overexpression of SHR in Arabidopsis thaliana induced substantial periclinal cell divisions in the ground tissue.However the detailed mechanism of SHR mediated periclinal cell division has not been fully explored.In this study,we analyzed the downstream genes induced by SHR in iSHR plants?induced overexpression of SHR?.We further conducted cellular and physiological experiments to explore regulatory mechanism of SHR based on transcriptome results.The results are summarized as follows:1.GO analysis showed that the oxidative respiratory burst enzymes RBOH A,C,D,E and F were significantly upregulated in iSHR plants.Together with the previous studies showing the involvement of ROS in middle cortex formation,we inferred that ROS participated in SHR mediated periclinal division.2.We further conducted NBT and DAB staining and found that the ROS content in iSHR root meristem was significantly higher than that in wild type?WT?.When iSHR roots were treated by the H₂O₂ scavenger,the periclinal division was significantly reduced compared with the Mock.However,the super oxygen scavenger treatment had no obvious effect on the division.In addition,we found that median level of H₂O₂ promoted the periclinal division in endodermis of WT,while high H₂O₂concentration caused apoptosis without inducing division.Exogenous H₂O₂ had no significant effect on the periclinal division of iSHR.However,H₂O₂ treatments could not promote periclinal division in shr-2.3.In view of the studies on salicylic acid?SA?and ROS in plant stress,we further found that SA could promote the division of the endodermis in WT to produce middle-cortex.ROS staining showed that H₂O₂ in this treatment was increased.Similar to H₂O₂ treatment,SA failed to induce periclinal cell division in shr-2 roots.At the same time,SA treatment of iSHR showed an nonsensical effect on the periclinal cell divisions.4.Through qRT-PCR experiments,we showed that SA biosynthetic genes were significantly upregulated by SHR.We thus inferred that SHR could indirectly maintain the ROS homeostasis by promoting the production of SA.5.It was previously reported that ROS level was considerably enhanced in spy-3 mutant.However,when SHR was overexpressed in spy-3,cell divisions in iSHR roots were not significantly increased.while the root apical stem cells were damaged by oxidative damageThe above results indicate that ROS provides an important microenvironment for SHR-mediated periclinal division.SHR promotes the accumulation of ROS by regulating NADPH Oxidase and promotes SA to maintain ROS microenvironment.Through the presence of SPY,maintain the relative homeostasis of ROS and protect cells from ROS damage.