Dynamic Cytology and Transcriptional Regulation of Rice Lamina Joint Development

Abstract

Rice (Oryza sativa) leaf angle is determined by lamina joint and is an important agricultural trait determining leaf erectness and, hence, the photosynthesis efficiency and grain yield. Genetic studies reveal a complex regulatory network of lamina joint development; however, the morphological changes, cytological transitions, and underlying transcriptional programming remain to be elucidated. A systemic morphological and cytological study reveals a dynamic developmental process and suggests a common but distinct regulation of the lamina joint. Successive and sequential cell division and expansion, cell wall thickening, and programmed cell death at the adaxial or abaxial sides form the cytological basis of the lamina joint, and the increased leaf angle results from the asymmetric cell proliferation and elongation. Analysis of the gene expression profiles at four distinct developmental stages ranging from initiation to senescence showed that genes related to cell division and growth, hormone synthesis and signaling, transcription (transcription factors), and protein phosphorylation (protein kinases) exhibit distinct spatiotemporal patterns during lamina joint development. Phytohormones play crucial roles by promoting cell differentiation and growth at early stages or regulating the maturation and senescence at later stages, which is consistent with the quantitative analysis of hormones at different stages. Further comparison with the gene expression profile of leaf inclination1, a mutant with decreased auxin and increased leaf angle, indicates the coordinated effects of hormones in regulating lamina joint. These results reveal a dynamic cytology of rice lamina joint that is fine-regulated by multiple factors, providing informative clues for illustrating the regulatory mechanisms of leaf angle and plant architecture.

The Rice Basic Helix–Loop–Helix 79 (OsbHLH079) Determines Leaf Angle and Grain Shape

“…This revealed that OsbHLH079 is mainly expressed in the stem, node, internode, and lamina joint (Figure 5a). Previous studies showed that several genes controlling leaf angle are highly expressed in the lamina joint, as is the case of OsbHLH079, and the degree of leaf inclination is mainly regulated by cell proliferation and/or cell expansion in the lamina joint, especially in the adaxial side of the lamina joint [5,20,21,41,[53][54][55][56][57]. Therefore, we speculated that the expression levels of cell proliferation-or expansion-related genes in lamina joint would be altered in osbhlh079-D, and thus compared the transcript levels of those genes in the lamina joint between WT and osbhlh079-D by RT-qPCR analysis.…”

“…Scanning electron microscopy was conducted as previously described with some modifications [92]. The lamina joints of flag leaves of WT and osbhlh079-D at heading stage grown under NLD conditions in the paddy field were excised and sectioned longitudinally as previously described [56]. The samples were fixed with modified Karnovsky's fixative (2% paraformaldehyde, 2% glutaraldehyde, and 50 mM sodium cacodylate buffer, pH 7.2) at 4 • C for 24 h, and washed with 50 mM sodium cacodylate buffer (pH 7.2) three times at 4 • C for 10 min each.…”

Genetics of barley tiller and leaf development

“…In contrast, excess in proliferation of parenchyma cells on the adaxial side results in enhanced leaf inclination (Zhao et al , ; Zhang et al ). Abnormal mechanical tissues, such as vascular bundle formation and cell wall composition in the lamina joint also play a crucial role in modification of leaf angle (Ning et al ), indicating a dynamic cytology of the lamina joint where multiple factors are involved in regulating its structure (Zhou et al ).…”

Defining chromatin state transitions predicts a network that modulates cell wall remodeling in phosphate-starved rice shoots

“…The signaling genes were mostly up-regulated, whereas the cell wall related genes were largely down-regulated. Comparing the transcriptomic profile of the CS4-CS3 DEGs to public transcriptome studies using Genevestigator (Hruz et al, 2008) revealed substantial overlap with several pairwise comparisons from a previous study on rice lamina joint development (Zhou et al, 2017). Comparisons between older stages of development (maturation or post-maturation) with a younger stage showed similar expression profiles as our CS4-CS3 Pi-deficiency DEGs (not shown).…”