Department of Biology, University of Minnesota Duluth, Duluth, MN 55812, USA.
Plant J. 2013 Jun;74(6):893-904. doi: 10.1111/tpj.12184. Epub 2013 May 2.
The PIN family of proteins is best known for its involvement in polar auxin transport and tropic responses. PIN6 (At1g77110) is one of the remaining PIN family members in Arabidopsis thaliana to which a biological function has not yet been ascribed. Here we report that PIN6 is a nectary-enriched gene whose expression level is positively correlated with total nectar production in Arabidopsis, and whose function is required for the proper development of short stamens. PIN6 accumulates in internal membranes consistent with the ER, and multiple lines of evidence demonstrate that PIN6 is required for auxin-dependent responses in nectaries. Wild-type plants expressing auxin-responsive DR5:GFP or DR5:GUS reporters displayed intense signal in lateral nectaries, but pin6 lateral nectaries showed little or no signal for these reporters. Further, exogenous auxin treatment increased nectar production more than tenfold in wild-type plants, but nectar production was not increased in pin6 mutants when treated with auxin. Conversely, the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) reduced nectar production in wild-type plants by more than twofold, but had no significant effect on pin6 lines. Interestingly, a MYB57 transcription factor mutant, myb57-2, closely phenocopied the loss-of-function mutant pin6-2. However, PIN6 expression was not dependent on MYB57, and RNA-seq analyses of pin6-2 and myb57-2 mutant nectaries showed little overlap in terms of differentially expressed genes. Cumulatively, these results demonstrate that PIN6 is required for proper auxin response and nectary function in Arabidopsis. These results also identify auxin as an important factor in the regulation of nectar production, and implicate short stamens in the maturation of lateral nectaries.
PIN 蛋白家族以其参与极性生长素运输和向性反应而闻名。PIN6（At1g77110）是拟南芥中剩余的 PIN 家族成员之一，其生物学功能尚未被赋予。在这里，我们报告 PIN6 是一个蜜腺丰富的基因，其表达水平与拟南芥总花蜜产量呈正相关，其功能对于短雄蕊的正常发育是必需的。PIN6 积累在内膜上，与内质网一致，多条证据表明 PIN6 是花蜜中生长素依赖性反应所必需的。表达生长素响应型 DR5:GFP 或 DR5:GUS 报告基因的野生型植物在侧蜜腺中显示出强烈的信号，但 pin6 侧蜜腺对这些报告基因的信号很少或没有。此外，外源生长素处理使野生型植物的花蜜产量增加了十倍以上，但生长素处理不能使 pin6 突变体的花蜜产量增加。相反，生长素运输抑制剂 N-1-萘基邻苯二甲酰胺（NPA）使野生型植物的花蜜产量减少了两倍以上，但对 pin6 系没有显著影响。有趣的是，一个 MYB57 转录因子突变体，myb57-2，与功能丧失突变体 pin6-2 非常相似。然而，PIN6 的表达并不依赖于 MYB57，并且 pin6-2 和 myb57-2 突变体蜜腺的 RNA-seq 分析表明，差异表达基因的重叠很少。综上所述，这些结果表明 PIN6 是拟南芥中生长素反应和蜜腺功能所必需的。这些结果还表明生长素是调节花蜜产量的一个重要因素，并暗示短雄蕊参与了侧蜜腺的成熟。
