Inhibition of brassinosteroid biosynthesis by either a dwarf4 mutation or a brassinosteroid biosynthesis inhibitor rescues defects in tropic responses of hypocotyls in the Arabidopsis mutant nonphototropic hypocotyl 4
Inhibition of brassinosteroid biosynthesis by either a dwarf4 mutation or a brassinosteroid biosynthesis inhibitor rescues defects in tropic responses of hypocotyls in the Arabidopsis mutant nonphototropic hypocotyl 4
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DOI：
10.1104/pp.105.076273
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发表时间：
2006-06-01
期刊：
影响因子：
7.4
通讯作者：
Yamamoto, Kotaro T.
中科院分区：
文献类型：
--
作者：
Nakamoto, Daisuke;Ikeura, Akimitsu;Yamamoto, Kotaro T.
拟南芥（Arabidopsis thaliana）的非向光性下胚轴4（nph 4）/生长素反应因子7（arf 7）突变体对生长素不敏感，并且在下胚轴向性、钩形成、差异叶生长和侧根形成方面存在缺陷。为了了解生长素通过NPH 4的信号转导途径，我们对nph 4 -103的抑制突变体进行了筛选，获得了一个矮秆抑制突变体，nph 4的抑制子（snp 2）。snp 2在黑暗条件下具有短的下胚轴，在光照条件下具有深绿色和圆形的叶、短叶柄和比野生型更多的侧枝。通过在光照和黑暗条件下向生长培养基中添加油菜素，snp 2表型得到拯救。遗传作图、序列分析和互补试验表明，snp 2是在油菜素类固醇（BR）生物合成中起作用的DWARF 4（DWF 4）的弱等位基因。SNP 2，被重新命名为DWF 4 -101，表现出类似于野生型的下胚轴的向光性和向重力性，在向重力性中具有稍快的响应。DWF 4 -101几乎完全抑制了NPH 4 -103下胚轴两种向性的缺陷，并完全抑制了NPH 4 -103叶片的低分化生长。用BR生物合成的抑制剂油菜新唑处理，也部分挽救了nph 4 -103中的向性缺陷。nph 4 - 103的下胚轴对生长素不敏感，而dwf 4 -101的下胚轴比野生型的下胚轴更敏感。DHF 4 -101 NPH 4 - 103下胚轴与DHF 4 -101下胚轴一样敏感。在nph 4 -103中，生长素诱导的massugu 2（MSG 2）/IAA 19基因表达减少。在dwf 4 -101和dwf 4 -101 nph 4 - 103中，MSG 2的mRNA水平降低，但两种突变体均表现出比野生型更强的生长素诱导MSG 2。综上所述，dwf 4 -101对nph 4 -103具有上位性。这些结果强烈表明，BR的缺陷抑制nph 4 -103缺陷的下胚轴和差异生长的叶片的向性反应和BR负调节向性反应。
The nonphototropic hypocotyl 4 ( nph4)/auxin response factor 7 ( arf7) mutant of Arabidopsis ( Arabidopsis thaliana) is insensitive to auxin and has defects in hypocotyl tropism, hook formation, differential leaf growth, and lateral root formation. To understand an auxin-signaling pathway through NPH4, we carried out screening of suppressor mutants of nph4-103 and obtained a dwarf suppressor mutant, suppressor of nph4 ( snp2). snp2 had short hypocotyls in the dark condition and dark green and round leaves, short petioles, and more lateral shoots than the wild type in the light condition. The snp2 phenotypes were rescued by adding brassinolide to the growth medium in both light and dark conditions. Genetic mapping, sequence analysis, and a complementation test indicated that snp2 was a weak allele of DWARF4 ( DWF4), which functions in brassinosteroid ( BR) biosynthesis. snp2, which was renamed dwf4-101, exhibited photo- and gravitropisms of hypocotyls similar to those of the wild type with a slightly faster response in gravitropism. dwf4-101 almost completely suppressed defects in both tropisms of nph4-103 hypocotyls and completely suppressed hyponastic growth of nph4-103 leaves. Treatment with brassinazole, an inhibitor of BR biosynthesis, also partially rescued the tropic defects in nph4-103. Hypocotyls of nph4- 103 were auxin insensitive, whereas hypocotyls of dwf4-101 were more sensitive than those of the wild type. dwf4-101 nph4- 103 hypocotyls were as sensitive as those of dwf4-101. Auxin inducibility of massugu 2 ( MSG2)/IAA19 gene expression was reduced in nph4-103. mRNA level of MSG2 was reduced in dwf4-101 and dwf4-101 nph4- 103, but both mutants exhibited greater auxin inducibility of MSG2 than the wild type. Taken together, dwf4-101 was epistatic to nph4-103. These results strongly suggest that BR deficiency suppresses nph4-103 defects in tropic responses of hypocotyls and differential growth of leaves and that BR negatively regulates tropic responses.