HD-ZIP IV gene Roc8 regulates the size of bulliform cells and lignin content in rice

The morphology of bulliform cells located on the upper epidermis of leaves is one of the most important cell structures affecting leaf shape. Although many mechanisms regulating the development of bulliform cells have been reported, the fine regulatory mechanisms governing this process have rarely been described. To identify novel components regulating rice leaf morphology, a mutant showing a constitutively rolling phenotype from the seedling stage to flowering, known ascrm1-D, was selected for further analysis. Anatomical analyses incrm1-Dwere attributable to the size reduction of bulliform cells. Thecrm1-Dwas controlled by a single dominant nuclear gene. Map-based cloning revealed thatRoc8,an HD zipper class IV family member, was responsible for thecrm1-Dphenotype. Notably, the 50-bp sequence in the 3 '-untranslated region (3 '-UTR) of theRoc8gene repressesRoc8at the translational level. Moreover, theroc8knockdown lines notably increased the size of bulliform cells. A series of assays revealed thatRoc8negatively regulates the size of bulliform cells. Unexpectedly,Roc8was also observed to positively mediate lignin biosynthesis without incurring a production penalty. The above results show thatRoc8may have a practical application in cultivating materials with high photosynthetic efficiency and low lignin content.