Gibberellin Biosynthetic Deficiency Is Responsible for Maize Dominant Dwarf11 (<i>D11</i>) Mutant Phenotype: Physiological and Transcriptomic Evidence

<div><p>Dwarf stature is introduced to improve lodging resistance and harvest index in crop production. In many crops including maize, mining and application of novel dwarf genes are urgent to overcome genetic bottleneck and vulnerability during breeding improvement. Here we report the characterization and expression profiling analysis of a newly identified maize dwarf mutant <i>Dwarf11</i> (<i>D11</i>). The <i>D11</i> displays severely developmental abnormalities and is controlled by a dominant Mendelian factor. The <i>D11</i> seedlings responds to both GA₃ and paclobutrazol (PAC) application, suggesting that dwarf phenotype of <i>D11</i> is caused by GA biosynthesis instead of GA signaling deficiency. In contrast, two well-characterized maize dominant dwarf plants <i>D8</i> and <i>D9</i> are all insensitive to exogenous GA₃ stimulation. Additionally, sequence variation of <i>D8</i> and <i>D9</i> genes was not identified in the <i>D11</i> mutant. Microarray and qRT-PCR analysis results demonstrated that transcripts encoding GA biosynthetic and catabolic enzymes <i>ent</i>-kaurenoic acid oxidase (KAO), GA 20-oxidase (GA20ox), and GA 2-oxidase (GA2ox) are up-regulated in <i>D11</i>. Our results lay a foundation for the following <i>D11</i> gene cloning and functional characterization. Moreover, results presented here may aid in crops molecular improvement and breeding, especially breeding of crops with plant height ideotypes.</p></div

DEGs involved in GA biosynthesis and catabolism.

<p>(<b>A</b>) GA biosynthesis and catabolism pathways were briefly diagramed. Transcripts encoding maize GA biosynthetic and catabolic enzymes ZmKAO, ZmGA20ox1, and ZmGA2ox8 are up-regulated in <i>D11</i>. (<b>B</b>) Semi-qRT-PCR validation of elevated transcripts <i>ZmKAO</i> and <i>ZmGA20ox1</i>. The <i>18S rRNA</i> gene was used as an internal control.</p

Gross morphology of maize <i>D11</i> mutant.

<p>(<b>A</b>) Phenotype of <i>D11</i> and wild type (WT). Bar  = 20 cm. (<b>B</b>) Whole plant. To get snapshot of internodes arrangement, leaves and spike were removed manually. Bar  = 20 cm. (<b>C</b>) Plant height. (<b>D</b>) Internodes. Bar  = 5 cm. (<b>E</b>) Internode length. (<b>F</b>) Leaf. Leaves of <i>D11</i> are slender, dark green, slightly-rolled, and with white margins. Bar  = 5 cm. (<b>G</b>) Roots. Aerial roots of <i>D11</i> display more sturdy. Bar  = 5 cm. (<b>H</b>) Spike. Spike of <i>D11</i> degenerates severely. Bar  = 5 cm. (<b>I</b>) Tassel. Bar  = 5 cm. (<b>J</b>) Anther. Anthers of <i>D11</i> are short and thin. Bar  = 1 mm. (<b>K</b>) Tassel branch number. (<b>L</b>) Length of central axis of tassel. In figures (C), (E), (K), and (L), data are mean ±SD (<i>n</i> = 30). Double asterisks denote significant difference at P≤0.01 level compared with the wild type by Student's <i>t</i> test.</p

Response of maize <i>D11</i> mutant to GA₃ and PAC application.

<p>(<b>A</b>) Seedlings of WT and <i>D11</i> when treated with a 10⁻⁴ M GA₃ solution. Bar  = 10 cm. (<b>B</b>) The second leaf sheath length of WT and <i>D11</i> (<i>n</i> = 35) when treated with a 10⁻⁴ M GA₃ solution. (<b>C</b>) Seedlings of WT and <i>D11</i> when treated with a 10⁻⁴ M PAC solution. Bar  = 10 cm. (<b>D</b>) Shoot length of WT and <i>D11</i> (<i>n</i> = 40) when treated with a 10⁻⁴ M PAC solution. In figures (B) and (D), data are mean ±SD. Double asterisks indicate significant difference at P≤0.01 level compared with untreated samples by Student's <i>t</i> test.</p