Brugière Norbert, Humbert Sabrina, Rizzo Nancy, Bohn Jennifer, Habben Jeffrey E
Discovery Group/Agronomic Traits, Pioneer Hi-Bred International, Inc., A DuPont Business, Johnston, IA 50131-0522, USA.
Plant Mol Biol. 2008 Jun;67(3):215-29. doi: 10.1007/s11103-008-9312-x.
Cytokinins (CKs) are plant hormones that regulate a large number of processes associated with plant growth and development such as induction of stomata opening, delayed senescence, suppression of auxin-induced apical dominance, signaling of nitrogen availability, differentiation of plastids and control of sink strength. In maize, CKs are thought to play an important role in establishing seed size and increasing seed set under normal and unfavorable environmental conditions therefore influencing yield. In recent years, the discovery of isopentenyl transferase (IPT) genes in plants has shed light on the CK biosynthesis pathway in plants. In an effort to increase our understanding of the role played by CKs in maize development and sink-strength, we identified several putative IPT genes using a bioinformatics approach. We focused our attention on one gene in particular, ZmIPT2, because of its strong expression in developing kernels. The expression of the gene and its product overlays the change in CK levels in developing kernels suggesting a major role in CK biosynthesis for kernel development. We demonstrate that at 8-10 days after pollination (DAP) the endosperm and especially the basal transfer cell layer (BETL) is a major site of ZmIPT2 expression, and that this expression persists in the BETL and the developing embryo into later kernel development stages. We show that ectopic expression of ZmIPT2 in calli and in planta created phenotypes consistent with CK overproduction. We also show that ZmIPT2 preferentially uses ADP and ATP over AMP as the substrates for dimethylallyl diphosphate (DMAPP) IPT activity. The expression pattern of ZmIPT2 in the BETL, endosperm and embryo during kernel development will be discussed with an emphasis on the suggested role of CKs in determining sink-strength and grain production in crop plants.
细胞分裂素（CKs）是一类植物激素，可调节大量与植物生长发育相关的过程，如诱导气孔开放、延缓衰老、抑制生长素诱导的顶端优势、氮素有效性信号传导、质体分化以及库强度控制。在玉米中，细胞分裂素被认为在正常和不利环境条件下确定种子大小和增加结实率从而影响产量方面发挥重要作用。近年来，植物中异戊烯基转移酶（IPT）基因的发现为植物细胞分裂素生物合成途径提供了线索。为了增进我们对细胞分裂素在玉米发育和库强度中所起作用的理解，我们采用生物信息学方法鉴定了几个假定的IPT基因。我们特别关注其中一个基因ZmIPT2，因为它在发育中的籽粒中强烈表达。该基因及其产物的表达与发育中籽粒细胞分裂素水平的变化重叠，表明其在籽粒发育的细胞分裂素生物合成中起主要作用。我们证明，在授粉后8 - 10天（DAP），胚乳尤其是基部转移细胞层（BETL）是ZmIPT2表达的主要部位，并且这种表达在BETL和发育中的胚中持续到籽粒发育后期。我们表明，ZmIPT2在愈伤组织和植株中的异位表达产生了与细胞分裂素过量产生一致的表型。我们还表明，ZmIPT2优先使用ADP和ATP而非AMP作为二甲基烯丙基二磷酸（DMAPP）IPT活性的底物。将讨论ZmIPT2在籽粒发育过程中在BETL、胚乳和胚中的表达模式，重点是细胞分裂素在决定作物库强度和籽粒产量中所暗示的作用。
