Plants have a chemically heterogeneous lipophilic layer, the cuticle, which protects them from biotic and abiotic stresses. The mechanisms that regulate cuticle development are poorly understood. We identified a rice (Oryza sativa) dominant curly leaf mutant, curly flag leaf1 (cfl1), and cloned CFL1, which encodes a WW domain protein. We overexpressed both rice and Arabidopsis CFL1 in Arabidopsis thaliana; these transgenic plants showed severely impaired cuticle development, similar to that in cfl1 rice. Reduced expression of At CFL1 resulted in reinforcement of cuticle structure. At CFL1 was predominantly expressed in specialized epidermal cells and in regions where dehiscence and abscission occur. Biochemical evidence showed that At CFL1 interacts with HDG1, a class IV homeodomain-leucine zipper transcription factor. Suppression of HDG1 function resulted in similar defective cuticle phenotypes in wild-type Arabidopsis but much alleviated phenotypes in At cfl1-1 mutants. The expression of two cuticle development-associated genes, BDG and FDH, was downregulated in At CFL1 overexpressor and HDG1 suppression plants. HDG1 binds to the cis-element L1 box, which exists in the regulatory regions of BDG and FDH. Our results suggest that rice and Arabidopsis CFL1 negatively regulate cuticle development by affecting the function of HDG1, which regulates the downstream genes BDG and FDH.

In plants, the meristem has to maintain a separate population of pluripotent cells that serve two main tasks, i.e., self‐maintenance and organ initiation, which are separated spatially in meristem. Prior to our study, WUS and WUS‐like WOX genes had been reported as essential for the development of the SAM. In this study, the consequences of gain of WOX1 function are described. Here we report the identification of an Arabidopsis gain‐of‐function mutant wox1‐D, in which the expression level of the WOX1 (WUSCHEL HOMEOBOX 1) was elevated and subtle defects in meristem development were observed. The wox1‐D mutant phenotype is dwarfed and slightly bushy, with a smaller shoot apex. The wox1‐D mutant also produced small and dark green leaves, and exhibited a failure in anther dehiscence and male sterility. Molecular evidences showed that the transcription of the stem cell marker gene CLV3 was down‐regulated in the meristem of wox1‐D but accumulated in the other regions, i.e., in the root‐hypocotyl junction and at the sites for lateral root initiation. The fact that the organ size and cell size in leaves of wox1‐D are smaller than those in wild type suggests that cell expansion is possibly affected in order to have partially retarded the development of lateral organs, possibly through alteration of CLV3 expression pattern in the meristem. An S‐adenosylmethionine decarboxylase (SAMDC) protein, SAMDC1, was found able to interact with WOX1 by yeast two‐hybrid and pull‐down assays in vitro. HPLC analysis revealed a significant reduction of polyamine content in wox1‐D. Our results suggest that WOX1 plays an important role in meristem development in Arabidopsis, possibly via regulation of SAMDC activity and polyamine homeostasis, and/or by regulating CLV3 expression.

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The second enzyme of the de novo purine biosynthesis pathway, PurD, is involved in leaf-colour development and the cell division process in rice.

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Transferring the genome of distant species to crops is an efficient way to create new germplasms. However, the molecular mechanisms involved are unclear. In this study, a new rice restorer line R21 with heat tolerance was created by introgressing the genomic DNA of sorghum into the recipient restorer line Jin Hui 1. Assembly of rice R21 and Jin Hui 1 genomes was performed using PacBio sequencing technology. Comparative genome analysis and coverage statistics showed that the repetitive sequence atr0026 was a candidate introgression fragment of sorghum DNA. Sequence similarity analysis revealed that atr0026 was distributed at different copy numbers on the telomeric position of chromosomes 9 or 10 in R21, Jin Hui 1, and several rice varieties, indicating that the repetitive sequence from sorghum was highly conserved in rice. The repeat annotation in Gramineae indicated that ribosomal DNA loci that existed in atr0026 may be cause a rearrangement of chromosomes 9 and 10 of the R21 genome, resulting in a copy number variation at the 5′ end of it. Our study lays the foundation for further elucidation of the molecular mechanisms underlying the heat tolerance of sorghum DNA introgression variant line R21, which is of great significance for guiding crop genetic breeding.

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