The Maize Hairy Sheath Frayed1 (Hsf1) Mutation Alters Leaf Patterning Through Increased Cytokinin Signaling

First author: Michael Muszynski; Affiliations: University of Hawaii (夏威夷大学): Honolulu, USA

Corresponding author: Michael Muszynski

Leaf morphogenesis requires growth polarized along three axes—proximal-distal, medial-lateral and abaxial-adaxial. Grass leaves display a prominent proximal-distal (P-D) polarity consisting of a proximal sheath separated from the distal blade by the auricle and ligule. Although proper specification of the four segments is essential for normal morphology, our knowledge is incomplete regarding the mechanisms which influence P-D specification in monocots like maize (Zea mays). Here we report the identification of the gene underlying the semi-dominant, leaf patterning, maize mutant Hairy Sheath Frayed1 (Hsf1). Hsf1 plants produce leaves with outgrowths consisting of proximal segments—sheath, auricle and ligule—emanating from the distal blade margin. Analysis of three independent Hsf1 alleles revealed gain-of-function missense mutations in the ligand binding domain of the maize cytokinin (CK) receptor Zea mays Histidine Kinase1 (ZmHK1) gene. Biochemical analysis and structural modeling suggest the mutated residues near the CK binding pocket affect CK binding affinity. Treatment of wild-type seedlings with exogenous CK phenocopied the Hsf1 leaf phenotypes. Results from expression and epistatic analyses indicated the Hsf1 mutant receptor appears to be hypersignaling. Our results demonstrate that hypersignaling of CK in incipient leaf primordia can reprogram developmental patterns in maize.

叶形态建成需要沿着三个轴向的极性生长，包括基-顶轴（proximal-distal）、中-侧轴（medial-lateral）以及背-腹轴（abaxial-adaxial）。草本叶的生长具有比较强烈的基-顶轴极性，主要表现在近端的鞘（sheath）与远端的叶片（blade）由叶耳（auricle）与叶舌（ligule）隔开。尽管这四个部分器官的特化对于草本叶形态的正确建成至关重要，但目前对于单子叶植物中影响基-顶轴极性的分子机制还不完善。本文中，作者报道了一个玉米半显性、影响叶模式建成的突变体Hsf1。Hsf1突变体植株形成的叶具有往外生长的表型，近端的组分鞘、叶耳以及叶舌会在远端叶片边缘处发出。对于三个独立的Hsf1株系分析显示，玉米细胞分裂素受体组氨酸激酶ZmHK1基因的配体结合结构域发生了错义突变，而这种突变似乎增强了该基因的功能。生化分析和结构建模显示细胞分裂素结合口袋（binding pocket）附近的残基突变会影响细胞分裂素结合活性。用外源细胞分裂素处理野生型的幼苗能够模拟Hsf1突变体的叶表型。表达和上位性分析显示Hsf1突变受体似乎是hypersignaling（超信号转导）。本文的结果表明，玉米中初生叶原基中细胞分裂素的超信号化可以重编程发育模式。

通讯：Michael Muszynski (https://manoa.hawaii.edu/ctahr/tpss/faculty?id=1035)

个人简介：1985年，托莱多大学，学士；1992年，爱荷华州立大学，博士。

研究方向：植物生长发育的分子调控机制。

doi: https://doi.org/10.1105/tpc.19.00677

Journal: Plant Cell

Published date: March 23, 2020