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

ABSTRACT: 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 as crm1-D, was selected for further analysis. Anatomical analyses in crm1-D were attributable to the size reduction of bulliform cells. The crm1-D was controlled by a single dominant nuclear gene. Map-based cloning revealed that Roc8, an HD zipper class IV family member, was responsible for the crm1-D phenotype. Notably, the 50-bp sequence in the 3'-untranslated region (3'-UTR) of the Roc8 gene represses Roc8 at the translational level. Moreover, the roc8 knockdown lines notably increased the size of bulliform cells. A series of assays revealed that Roc8 negatively regulates the size of bulliform cells. Unexpectedly, Roc8 was also observed to positively mediate lignin biosynthesis without incurring a production penalty. The above results show that Roc8 may have a practical application in cultivating materials with high photosynthetic efficiency and low lignin content.

SUBMITTER: Sun J

PROVIDER: S-EPMC7680540 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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

Sun Jing J Cui Xuean X Teng Shouzhen S Kunnong Zhao Z Wang Yanwei Y Chen Zhenhua Z Sun Xuehui X Wu Jinxia J Ai Pengfei P Quick William Paul WP Lu Tiegang T Zhang Zhiguo Z

Plant biotechnology journal 20200708 12

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 as crm1-D, was selected for ...[more]

PMID: 32559019

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Project description:BackgroundPlant HD-Zip transcription factors are modular proteins in which a homeodomain is associated to a leucine zipper. Of the four subfamilies in which they are divided, the tested members from subfamily I bind in vitro the same pseudopalindromic sequence CAAT(A/T)ATTG and among them, several exhibit similar expression patterns. However, most experiments in which HD-Zip I proteins were over or ectopically expressed under the control of the constitutive promoter 35S CaMV resulted in transgenic plants with clearly different phenotypes. Aiming to elucidate the structural mechanisms underlying such observation and taking advantage of the increasing information in databases of sequences from diverse plant species, an in silico analysis was performed. In addition, some of the results were also experimentally supported.ResultsA phylogenetic tree of 178 HD-Zip I proteins together with the sequence conservation presented outside the HD-Zip domains allowed the distinction of six groups of proteins. A motif-discovery approach enabled the recognition of an activation domain in the carboxy-terminal regions (CTRs) and some putative regulatory mechanisms acting in the amino-terminal regions (NTRs) and CTRs involving sumoylation and phosphorylation. A yeast one-hybrid experiment demonstrated that the activation activity of ATHB1, a member of one of the groups, is located in its CTR. Chimerical constructs were performed combining the HD-Zip domain of one member with the CTR of another and transgenic plants were obtained with these constructs. The phenotype of the chimerical transgenic plants was similar to the observed in transgenic plants bearing the CTR of the donor protein, revealing the importance of this module inside the whole protein.ConclusionsThe bioinformatical results and the experiments conducted in yeast and transgenic plants strongly suggest that the previously poorly analyzed NTRs and CTRs of HD-Zip I proteins play an important role in their function, hence potentially constituting a major source of functional diversity among members of this subfamily.

Project description:BackgroundHomeodomain-leucine zipper (HD-ZIP) transcription factors play important roles in the growth, development and stress responses of plants, including (presumably) physic nut (Jatropha curcas), which has high drought and salinity tolerance. However, although physic nut's genome has been released, there is little knowledge of the functions, expression profiles and evolutionary histories of the species' HD-ZIP genes.ResultsIn this study, 32 HD-ZIP genes were identified in the physic nut genome (JcHDZs) and divided into four groups (I-IV) based on phylogenetic analysis with homologs from rice, maize and Arabidopsis. The analysis also showed that most of the JcHDZ genes were closer to members from Arabidopsis than to members from rice and maize. Of the 32 JcHDZ genes, most showed differential expression patterns among four tissues (root, stem cortex, leaf, and seed). Expression profile analysis based on RNA-seq data indicated that 15 of the JcHDZ genes respond to at least one abiotic stressor (drought and/or salinity) in leaves at least at one time point. Transient expression of a JcHDZ16-YFP fusion protein in Arabidopsis protoplasts cells showed that JcHDZ16 is localized in the nucleus. In addition, rice seedlings transgenically expressing JcHDZ16 had lower proline contents and activities of antioxidant enzymes (catalase and superoxide dismutase) together with higher relative electrolyte leakage and malondialdehyde contents under salt stress conditions (indicating higher sensitivity) than wild-type plants. The transgenic seedlings also showed increased sensitivity to exogenous ABA, and increases in the transcriptional abundance of several salt stress-responsive genes were impaired in their responses to salt stress. Further data on JcHDZ16-overexpressing plants subjected to salt stress treatment verified the putative role of JcHDZ genes in salt stress responses.ConclusionOur results may provide foundations for further investigation of functions of JcHDZ genes in responses to abiotic stress, and promote application of JcHDZ genes in physic nut breeding.

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

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

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