Gene expression profiling of sav mutants

Plants grown at high densities perceive a decrease in the red to far-red (R:FR) ratio of incoming light, resulting from absorption of red light by canopy leaves and reflection of far-red light from neighboring plants. These changes in light quality trigger a series of responses known collectively as the shade avoidance syndrome. During shade avoidance, stems elongate at the expense of leaf and storage organ expansion, there is reduced branching, and flowering is accelerated. We identified several loci in Arabidopsis, mutations in which lead to plants defective in multiple shade avoidance outputs. Here we describe SAV3, an aminotransferase, and show that SAV3 catalyzes the formation of indole-3-pyruvic acid (IPA) from L-tryptophan (L-Trp), the first step in a previously proposed, but uncharacterized, auxin biosynthetic pathway. This pathway can be rapidly deployed to biosynthesize auxin at the high levels required to initiate the multiple changes in body plan associated with shade avoidance. Keywords: shade avoidance auxin brassinosteroid Wild type Col-0, sav3-2 and sav1-1 seedlings were used here. They were treated with or without 1hr of low R:FR light (R:FR ratio=0.7). Three independent biological replicates were used.

高密度种植的植物可感知入射光中红光与远红光（R:FR）比值的下降，该现象源于冠层叶片对红光的吸收以及邻近植株对远红光的反射。这种光质变化会触发一系列被统称为避荫综合征（shade avoidance syndrome）的响应过程。在避荫过程中，植株会以叶片和储藏器官的发育为代价促进茎秆伸长，同时分枝受到抑制，开花进程提前。
我们在拟南芥（Arabidopsis）中鉴定到多个位点，这些位点发生突变后会导致植株在多项避荫相关性状上存在缺陷。本研究报道了氨基转移酶（aminotransferase）SAV3，并证实其可催化L-色氨酸（L-tryptophan，L-Trp）合成吲哚-3-丙酮酸（indole-3-pyruvic acid，IPA）——这是此前被提出但尚未被表征的生长素生物合成途径的第一步。该途径可被快速激活，以合成避荫响应所需的高浓度生长素，进而启动与避荫相关的植株体型多重变化。
关键词：避荫、生长素、油菜素类固醇（brassinosteroid）。本研究使用了野生型Col-0、sav3-2及sav1-1幼苗，分别经1小时低R:FR光（R:FR比值=0.7）处理或不做处理，每组设置3次独立生物学重复。