Abstract
Rice (Oryza sativa) has long and narrow leaves with parallel veins, similar to other grasses. Relative to Arabidopsis thaliana which has oval-shaped leaves, our understanding of the mechanism of leaf development is insufficient in grasses. In this study, we show that OsWOX4, a member of the WUSCHEL-RELATED HOMEOBOX gene family, plays important roles in early leaf development in rice. Inducible downregulation of OsWOX4 resulted in severe defects in leaf development, such as an arrest of vascular differentiation, a partial defect in the early cell proliferation required for midrib formation, and a failure to maintain cellular activity in general parenchyma cells. In situ analysis showed that knockdown of OsWOX4 reduced the expression of two LONELY GUY genes, which function in the synthesis of active cytokinin, in developing vascular bundles. Consistent with this, cytokinin levels were downregulated by OsWOX4 knockdown. Transcriptome analysis further showed that OsWOX4 regulates multiple genes, including those responsible for cell cycle progression and hormone action, consistent with the effects of OsWOX4 downregulation on leaf phenotypes. Collectively, these results suggest that OsWOX4 acts as a key regulator at an early stage of leaf development. Our previous work revealed that OsWOX4 is involved in the maintenance of shoot apical meristem in rice, whereas AtWOX4 is specifically associated with the maintenance of vascular stem cells in Arabidopsis. Thus, the function of the two orthologous genes seems to be diversified between rice and Arabidopsis.
Highlights
Proper leaf development in plants is crucial for their body plan and for efficient photosynthesis
OsWOX4 function in leaf development was supported by a JSPS Fellowship from the Japan Society for the Promotion of Science (201506957)
OsWOX4 was expressed in the leaf primordia, in addition to the shoot apical meristem (SAM) (Fig 1A to 1E)
Summary
Proper leaf development in plants is crucial for their body plan and for efficient photosynthesis. Plants are sessile organisms that evolve morphological leaf traits by optimization to their respective natural habitats. Leaf primordia start growing out via cell proliferation, and differentiate into several types of tissue [2]. The molecular mechanism of leaf development has been well studied in Arabidopsis thaliana, which has oval-shaped leaves with reticulated veins [3]. Our understanding of leaf development in monocots such as grasses, which have long and narrow leaves with parallel veins, remains limited despite their agronomic importance. There is less information about the key genes that regulate early leaf development including cell proliferation and tissue differentiation in leaf primordia
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