Yu Lin, Yu Xuhong, Shen Ruijuan, He Yuke
National Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai, 200032, China.
Planta. 2005 May;221(2):231-42. doi: 10.1007/s00425-004-1439-7. Epub 2004 Dec 3.
For genetic analysis of the mechanism of leaf curvature, we chose hyl1 mutant of Arabidopsis as a model for dissection of leaf venation pattern and adaxial/abaxial polarity. In leaves of hyl1 mutants that were hyponastic and curved upward, the complexity of the secondary veins was reduced, and the discontinuity of veins increased. In the lateral areas of the leaves where transverse curvature arises, dorsoventral polarity was lost due to the unclear spongy cells, and the epidermal cells became smaller on the adaxial surface than those of the abaxial surface, whereas the number of epidermal cells on the two surfaces were almost the same. In this case, less complexity of venation, decreased cell growth on the adaxial surface was attributed to leaf curvature. To depict the role of HYL1 in leaf venation and polarity, we constructed pHYL1:: GUS to drive the uidA (beta-glucuronidase) gene, and observed that the GUS signal appeared primarily in the petioles and mid-veins of rosette leaves, and were restricted to vascular tissues, demonstrating that HYL1 promoter directs the process of leaf venation by the uneven expression of the HYL1 gene in leaves. In situ hybridization indicates that HYL1 gene is preferentially expressed in leaf blades as well as vasculature. In curved leaves of hyl1 mutants, the expression level of adaxial identity gene REV was increased and the expression position restricted mainly in vasculature and on both sides of growing leaves near the margins while expression of the miR165 gene was remarkably reduced, suggesting that HYL1 maintain venation and polarity of growing leaves by altering the level of microRNA that direct the cleavage of REV transcripts.
为了对叶片卷曲机制进行遗传分析，我们选择拟南芥的hyl1突变体作为剖析叶脉模式和近轴/远轴极性的模型。在向上卷曲且叶片下弯的hyl1突变体叶片中，二级叶脉的复杂性降低，叶脉的不连续性增加。在叶片出现横向卷曲的外侧区域，由于海绵细胞不清晰，背腹极性丧失，近轴表面的表皮细胞比远轴表面的小，而两个表面的表皮细胞数量几乎相同。在这种情况下，叶脉复杂性降低、近轴表面细胞生长减少被认为是叶片卷曲的原因。为了描述HYL1在叶脉和极性中的作用，我们构建了pHYL1::GUS来驱动uidA（β-葡萄糖醛酸酶）基因，并观察到GUS信号主要出现在莲座叶的叶柄和主脉中，且局限于维管组织，这表明HYL1启动子通过叶片中HYL1基因的不均匀表达来指导叶脉形成过程。原位杂交表明，HYL1基因在叶片以及脉管系统中优先表达。在hyl1突变体的卷曲叶片中，近轴身份基因REV的表达水平升高，表达位置主要局限于维管组织以及生长叶片边缘附近的两侧，而miR165基因的表达显著降低，这表明HYL1通过改变指导REV转录本切割的微小RNA水平来维持生长叶片的叶脉和极性。
