Abstract
BackgroundThe Class III homeodomain Leu zipper (HD-Zip III) gene family plays important roles in plant growth and development. Here, we analyze the function of OsHox32, an HD-Zip III family member, and show that it exhibits pleiotropic effects on regulating plant type architecture and leaf development in rice.ResultsTransgenic lines overexpressing OsHox32 (OsHox32-OV) produce narrow leaves that roll towards the adaxial side. Histological analysis revealed a decreased number of bulliform cells in OsHox32-OV lines. In addition, the angle between the leaf and culm was reduced, resulting in an erect plant phenotype. The height of the plants was reduced, resulting in a semi-dwarf phenotype. In addition, the chlorophyll level was reduced, resulting in a decrease in the photosynthetic rate, but water use efficiency was significantly improved, presumably due to the rolled leaf phenotype. OsHox32 exhibited constitutive expression in different organs, with higher mRNA levels in the stem, leaf sheath, shoot apical meristems and young roots, suggesting a role in plant-type and leaf development. Moreover, OsHox32 mRNA levels were higher in light and lower in the dark under both long-day and short-day conditions, indicating that OsHox32 may be associated with light regulation. Photosynthesis-associated and chlorophyll biosynthesis-associated genes were down-regulated to result in the reduction of photosynthetic capacity in OsHox32-OV lines. mRNA level of six rice YABBY genes is up-regulated or down-regulated by OsHox32, suggesting that OsHox32 may regulate the architecture of plant type and leaf development by controlling the expression of YABBY genes in rice. In addition, OsHox32 mRNA level was induced by the phytohormones, indicating that OsHox32 may be involved in phytohormones regulatory pathways.ConclusionsOsHox32, an HD-Zip III family member, plays pleiotropic effects on plant type architecture and leaf development in rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0118-1) contains supplementary material, which is available to authorized users.
Highlights
The Class III homeodomain Leu zipper (HD-Zip III) gene family plays important roles in plant growth and development
OsHox9 and OsHox10 are more similar to the two maize (Zea mays) members RLD1 and RLD2, which play an important role in establishing the adaxial/abaxial polarity of the maize leaf
Our results showed that photosynthetic rate (Pn), Gs and transpiration rate (Tr) were significantly reduced, whereas water use efficiency (WUE) was significantly improved in the penultimate and antepenultimate leaves of OsHox32OV plants compared with wild type plants (Fig. 3a, b, d, and e), suggesting that the rolled leaf phenotype in OsHox32-OV lines affects stomatal conductance and reduces transpiration to improve WUE
Summary
The Class III homeodomain Leu zipper (HD-Zip III) gene family plays important roles in plant growth and development. We analyze the function of OsHox, an HD-Zip III family member, and show that it exhibits pleiotropic effects on regulating plant type architecture and leaf development in rice. Rice outermost cell-specific gene (Roc5), a member of homeodomain leucine zipper class IV, controls leaf rolling by regulating bulliform cell fate and development (Zou et al 2011). SEMI-ROLLED LEAF1 (SRL1), a glycosylphosphatidylinositol-anchored protein, was found to regulate the formation of bulliform cells in the adaxial cell layers, leading to leaf rolling in rice (Xiang et al 2012). A zinc finger homeodomain class homeobox transcription factor (OsZHD1) was found in rice to induce abaxially curling and drooping due to increased bulliform cell numbers (Xu et al 2014)
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