Cytological Mechanism Of Rolled-leaf Formation And Functional Analysis Of OUL1Controlling Leaf Rolling In Rice

Rice is a leading cereal crop and main staple food for over half of the world population. Withaccretion of population and arable land decrease, steady increase in rice production only depends onincreasing per unit area yield. Nevertheless, improvement of plant type in rice plays an important rolein it. Leaf shape has long been considered an important agronomic trait in rice. Moderate leaf rollingin rice leads to erect leaf canopies and higher photosynthetic efficiency, improving stress response byreducing transpirational water loss and radiant heat absorption, thereby increasing grain yield.Therefore, moderate leaf rolling is an ideal trait for rice breeding.It is possible that leaf rollingphenotypes are resulted from changes of any cell types making up leaf blade. During screening ofrice T-DNA insertion lines, more than300stable mutants showing various leaf rolling phenotypeswere obtained. Cytological analysis of those mutants indicated that changes of number, size andpattern of bulliform cells, sclerenchymatous cells, parenchyma cells, mesophyll cells as well asvascular bundle could lead to leaf rolling. Those mutants have been categorized into8groupsaccording to their cytological characteristics: increased bulliform cell number and area, decreasedbulliform cell number and area, disordered bulliform cell number and area, partial sclerenchymatouscell absence, phloem expansion of vascular system, increased parenchyma cell, a few cell typeschange, partial mesophyll cells become parenchyma cell-like.To understand the molecular mechanism controlling leaf rolling, we screened a rice T-DNAinsertion population and isolated the outcurved leaf1(oul1) mutant showing abaxial leaf rolling. Thephenotypes were caused by knockout of Roc5, an ortholog of the Arabidopsis homeodomain leucinezipper (HD-Zip) class IV gene GLABRA2. Interestingly, overexpression of Roc5led to adaxiallyrolled leaves, whereas cosuppression of Roc5resulted in abaxial leaf rolling. Bulliform cell numberand size increased in oul1and Roc5cosuppression plants but were reduced in Roc5-overexpressinglines. The data indicate that Roc5negatively regulates bulliform cell fate and development. Geneexpression profiling, quantitative PCR, and RNA interference analyses revealed that ProtodermalFactor Like was probably downregulated in oul1. The mRNA level of PFL was increased inRoc5-overexpressing lines, and PFL-RNAi transgenic plants exhibit reversely rolling leaves byreason of increase of bulliform cell number and size, indicating that Roc5may have a conservedfunction. These are the first functional data for a gene encoding an HD-Zip IV transcriptional factorin rice that modulates leaf rolling.