United States Department of Agriculture-Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, Chemistry Unit, Gainesville, Florida 32608-1069, USA.
Plant Physiol. 2010 May;153(1):306-18. doi: 10.1104/pp.110.155226. Epub 2010 Mar 17.
The maize (Zea mays) Miniature1 (Mn1) locus encodes the cell wall invertase INCW2, which is localized predominantly in the basal endosperm transfer layer of developing kernels and catalyzes the conversion of sucrose into glucose and fructose. Mutations in Mn1 result in pleiotropic changes, including a reduction in kernel mass and a recently reported decrease in indole-3-acetic acid (IAA) levels throughout kernel development. Here, we show that mn1-1 basal kernel regions (pedicels and basal endosperm transfer layer) accumulate higher levels of sucrose and lower levels of glucose and fructose between 8 and 28 d after pollination when compared with the wild type, whereas upper regions of mn1 accumulate similar or increased concentrations of sugars. To determine the cause of the reduction in IAA accumulation, we investigated transcript levels of several potential IAA biosynthetic enzymes. We demonstrate that reduced IAA levels most closely correspond to reduced transcript levels of ZmYUCCA (ZmYUC), a newly identified homolog of the Arabidopsis (Arabidopsis thaliana) gene YUCCA. We further demonstrate that ZmYUC catalyzes the N-hydroxylation of tryptamine and that sugar levels regulate transcript levels of ZmYUC, both in in vitro-cultured kernels and in a promoter-reporter fusion in Arabidopsis. These results indicate that developing seeds may modulate growth by altering auxin biosynthesis in response to sugar concentrations.
玉米（Zea mays）微型 1（Mn1）基因座编码细胞壁转化酶 INCW2，该酶主要定位于发育中的胚乳转移层的基部，催化蔗糖转化为葡萄糖和果糖。Mn1 突变导致多效性变化，包括胚乳质量减少以及最近报道的整个胚乳发育过程中吲哚-3-乙酸（IAA）水平降低。在这里，我们表明，mn1-1 胚乳基部区域（花梗和胚乳转移层）在授粉后 8 至 28 天之间积累了更高水平的蔗糖和更低水平的葡萄糖和果糖，而 mn1 的上部区域则积累了类似或增加的糖浓度。为了确定 IAA 积累减少的原因，我们研究了几种潜在的 IAA 生物合成酶的转录水平。我们证明，IAA 水平的降低与玉米基因 ZmYUCCA（ZmYUC）的转录水平降低密切相关，ZmYUC 是拟南芥（Arabidopsis thaliana）基因 YUCCA 的新鉴定同源物。我们进一步证明，ZmYUC 催化色胺的 N-羟化，并且糖水平调节 ZmYUC 的转录水平，无论是在体外培养的胚乳中还是在拟南芥中的启动子-报告基因融合中。这些结果表明，发育中的种子可能通过响应糖浓度改变生长素生物合成来调节生长。
