Instituto de Agrobiotecnología del Litoral, Universidad Nacional del Litoral, CONICET, CC 242 Ciudad Universitaria, 3000, Santa Fe, Argentina.
Instituto de Agrobiotecnología del Litoral, Universidad Nacional del Litoral, CONICET, CC 242 Ciudad Universitaria, 3000, Santa Fe, Argentina
J Exp Bot. 2015 Sep;66(19):5929-43. doi: 10.1093/jxb/erv302. Epub 2015 Jul 1.
AtHB13 is a homeodomain leucine zipper I transcription factor whose function in development is largely unknown. AtHB13 and AtHB23 mutant and silenced lines were characterized by expression studies, reciprocal crosses, complementation, molecular analyses, and developmental phenotypes. The athb13-1 and athb13-2 mutants, athb23 silenced, and athb13/athb23 double-silenced plants exhibited faster elongation rates of their inflorescence stems, whereas only athb13-1 and the double-knockdown athb13/athb23 exhibited shorter siliques, fewer seeds, and unfertilized ovules compared with the wild type (WT). The cell sizes of mutant and WT plants were similar, indicating that these transcription factors probably affect cell division. Reciprocal crosses between athb13-1 and the WT genotype indicated that the silique defect was male specific. Pollen hydration assays indicated that the pollen grains of the athb13-1 mutant were unable to germinate on stigmas. AtHB23-silenced plants exhibited normal siliques, whereas double-knockdown athb13/athb23 plants were similar to athb13-1 plants. Both AtHB13 and AtHB23 were able to rescue the abnormal silique phenotype. AtHB23 was upregulated in athb13-2 plants, whereas its transcript levels in athb13-1 mutants were not significantly increased. Transcriptome analysis comparing athb13-1 and WT inflorescences revealed that a large number of genes, including several involved in pollen coat formation, are regulated by AtHB13. Finally, athb13-1 complementation with mutated versions of AtHB13 confirmed that two different tryptophans in its C terminus are essential. We conclude that AtHB13 and AtHB23 play independent, negative developmental roles in stem elongation, whereas only AtHB13 is crucial for pollen germination. Furthermore, AtHB23, which does not normally exert a functional role in pollen, can act as a substitute for AtHB13.
AtHB13 是一个同源域亮氨酸拉链 I 转录因子，其在发育中的功能很大程度上是未知的。通过表达研究、正反交、互补、分子分析和发育表型对 AtHB13 和 AtHB23 突变体和沉默系进行了表征。athb13-1 和 athb13-2 突变体、athb23 沉默以及 athb13/athb23 双沉默植物的花序茎伸长率更快，而只有 athb13-1 和双敲除 athb13/athb23 的短角果更短、种子更少、未受精的胚珠与野生型 (WT) 相比。突变体和 WT 植物的细胞大小相似，表明这些转录因子可能影响细胞分裂。athb13-1 与 WT 基因型的正反交表明，短角果缺陷是雄性特有的。花粉水合测定表明，athb13-1 突变体的花粉粒无法在柱头上萌发。AtHB23 沉默的植物表现出正常的短角果，而双敲除 athb13/athb23 的植物与 athb13-1 植物相似。AtHB13 和 AtHB23 都能够挽救异常短角果表型。athb13-2 植物中 AtHB23 上调，而 athb13-1 突变体中的其转录水平没有显著增加。比较 athb13-1 和 WT 花序的转录组分析表明，大量基因，包括几个参与花粉外壳形成的基因，受 AtHB13 调控。最后，athb13-1 与 AtHB13 的突变版本互补证实其 C 端的两个不同色氨酸是必需的。我们得出结论，AtHB13 和 AtHB23 在茎伸长的发育中起着独立的负向作用，而只有 AtHB13 对花粉萌发至关重要。此外，在花粉中通常不起功能作用的 AtHB23 可以作为 AtHB13 的替代物。
