Hydrogen peroxide homeostasis provides beneficial micro-environment for SHR-mediated periclinal division inArabidopsisroot

The precise regulation of asymmetric cell division (ACD) is essential for plant organogenesis. InArabidopsisroots, SHORT-ROOT (SHR) functions to promote periclinal division in cortex/endodermis initials, which generate the ground tissue patterning. Although multiple downstream transcription factors and interplaying hormone pathways have been reported, the cellular mechanism that affects SHR-mediated periclinal division remains largely unclear. Here, we found that SHR can substantially elevate reactive oxygen species (ROS) levels inArabidopsisroots by activating respiratory burst oxidase homologs (RBOHs). Among the ROS products, hydrogen peroxide (H2O2) rather than superoxide (O-2(-)) was shown to play a critical role in SHR-mediated periclinal division. Scavenging H(2)O(2)could markedly impair the ability of SHR to induce periclinal division. We also show that salicylic acid (SA) can promote H(2)O(2)production by repressingCATexpression, which greatly increased periclinal division in root endodermis. As a result, middle cortex was more frequently formed in the endodermis ofsnc1, a mutant with accumulated endogenous SA and H2O2. In addition to RBOHs, SHR also activated the SA pathway, which might contribute to the elevated H(2)O(2)level induced by SHR. Thus, our data suggest a mechanism by which SHR creates the optimal micro-environment for periclinal division by maintaining ROS homeostasis inArabidopsisroots.