Plasma membrane NADPH oxidases (Noxs) are key producers of reactive oxygen species under both normal and stress conditions in plants. We demonstrate that at least eleven genes in the genome of rice (Oryza sativa L.) were predicted to encode Nox proteins, including nine genes (OsNox1–9) that encode typical Noxs and two that encode ancient Nox forms (ferric reduction oxidase 1 and 7, OsFRO1 and OsFRO7). Phylogenetic analysis divided the Noxs from nine plant species into six subfamilies, with rice Nox genes distributed among subfamilies I to V. Gene expression analysis using semi-quantitative RT-PCR and real-time qRT-PCR indicated that the expression of rice Nox genes depends on organs and environmental conditions. Exogenous calcium strongly stimulated the expression of OsNox3, OsNox5, OsNox7, and OsNox8, but depressed the expression of OsFRO1. Drought stress substantially upregulated the expression of OsNox1–3, OsNox5, OsNox9, and OsFRO1, but downregulated OsNox6. High temperature upregulated OsNox5–9, but significantly downregulated OsNox1–3 and OsFRO1. NaCl treatment increased the expression of OsNox2, OsNox8, OsFRO1, and OsFRO7, but decreased that of OsNox1, OsNox3, OsNox5, and OsNox6. These results suggest that the expression profiles of rice Nox genes have unique stress-response characteristics, reflecting their related but distinct functions in response to different environmental stresses.

Summary: Leaf rolling is considered as one of the most important agronomic traits in rice breeding. It has been previously reported that SEMI‐ROLLED LEAF 1 (SRL1) modulates leaf rolling by regulating the formation of bulliform cells in rice (Oryza sativa); however, the regulatory mechanism underlying SRL1 has yet to be further elucidated. Here, we report the functional characterization of a novel leaf‐rolling mutant, curled leaf and dwarf 1 (cld1), with multiple morphological defects. Map‐based cloning revealed that CLD1 is allelic with SRL1, and loses function in cld1 through DNA methylation. CLD1/SRL1 encodes a glycophosphatidylinositol (GPI)‐anchored membrane protein that modulates leaf rolling and other aspects of rice growth and development. The cld1 mutant exhibits significant decreases in cellulose and lignin contents in secondary cell walls of leaves, indicating that the loss of function of CLD1/SRL1 affects cell wall formation. Furthermore, the loss of CLD1/SRL1 function leads to defective leaf epidermis such as bulliform‐like epidermal cells. The defects in leaf epidermis decrease the water‐retaining capacity and lead to water deficits in cld1 leaves, which contribute to the main cause of leaf rolling. As a result of the more rapid water loss and lower water content in leaves, cld1 exhibits reduced drought tolerance. Accordingly, the loss of CLD1/SRL1 function causes abnormal expression of genes and proteins associated with cell wall formation, cuticle development and water stress. Taken together, these findings suggest that the functional roles of CLD1/SRL1 in leaf‐rolling regulation are closely related to the maintenance of cell wall formation, epidermal integrity and water homeostasis.

Rice leaves are important energy source for the whole plant. An optimal structure will be beneficial for rice leaves to capture light energy and exchange gas, thus increasing the yield of rice. Moderate leaf rolling and relatively erect plant architecture may contribute to high yield of rice, but the relevant molecular mechanism remains unclear. In this study, we identified and characterized a rolling and erect leaf mutant in rice and named it as rel2. Histological analysis showed that the rel2 mutant has increased number of bulliform cells and reduced size of middle bulliform cells. We firstly mapped REL2 to a 35-kb physical region of chromosome 10 by map-based cloning strategy. Further analysis revealed that REL2 encodes a protein containing DUF630 and DUF632 domains. In rel2 mutant, the mutation of two nucleotide substitutions in DUF630 domain led to the loss-of-function of REL2 locus and the function of REL2 could be confirmed by complementary expression of REL2 in rel2 mutant. Further studies showed that REL2 protein is mainly distributed along the plasma membrane of cells and the REL2 gene is relatively higher expressed in younger leaves of rice. The results from quantitative RT-PCR analysis indicated that REL2 functioning in the leaf shape formation might have functional linkage with many genes associated with the bulliform cells development, auxin synthesis and transport, etc. REL2 is the DUF domains contained protein which involves in the control of leaf rolling in rice. It is the plasma membrane localization and its functions in the control of leaf morphology might involve in multiple biological processes such as bulliform cell development and auxin synthesis and transport.

The soil environment, crop growth and fruit quality of melons are negatively affected by long-term continuous cropping. It is important to study the mechanism of continuous cropping obstacles and their biological control.