Maize nac1 and cld genes map to chromosome arms 10L and 2S, and to 4L and 5L, respectively.

Abstract

The reactions of plants to NaCl [1], cold [2] and heat stresses [3] are related to programmed cell death. Nac1, a gene in maize coding for NaCl stress protein 1, homologous to the mammalian salt stress resistance gene nac, potentially functions in the reaction to NaCl stress. Cld, a gene coding for cold-regulated protein, is highly expressed in extreme temperature situations, or in cold or heat shock. Maize (Zea mays L.) inbred line Huang Zao 4 was donated by Professor Song JianCheng, Shandong Agricultural University, China. The cDNA probes tested, nac1 (550 bp) and csu19 (1.6 kb) cloned in vectors pZL1 and pBS and specific for the genes nac1 and cld respectively, were kindly supplied by the UMC Clone Distribution Coordinator, University of Missouri-Columbia, USA, and were labelled with Bio-11-dUTP by nick translation. Metaphase chromosome preparations were made as described by Song and Gustafson [4]. In situ hybridisation and fluorescence detection followed the protocol outlined by Dong and Quick [5] with a little modification. The slides were counterstained with 3 μg/ml propidium iodide containing 10 μg/ml p-phenylenediamine dihydrochloride, and visualised with an Olympus fluorescence microscope (BX60). Chromosomes were identified by their relative lengths and arm ratios following the standard karyotype [6]. Results are shown in Table 1; they confirmed the positions of nac1 and cld on linkage groups 10 and 4 on the genetic map, and duplicated sequences homologous to these two genes were also found on 2S and 5L. The latter did not show any site on the genetic map, demonstrating they had no corresponding phenotypes.