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Previously implicated in permitting unhindered growth of etiolated seedlings through the soil after germination, the apical hook must be protected against mechanical impedance

Previously implicated in permitting unhindered growth of etiolated seedlings through the soil after germination, the apical hook must be protected against mechanical impedance. the apical hook and inflorescences were preferred isopod targets in JA-deficient plants that could be rescued by exogenously administered JA, our data identify a JA-dependent mechanism of plant arthropod deterrence that is recalled in different organs and at quite different times of plant development. attacked by herbivores, volatiles to recruit the herbivores’ natural enemies1,2 and secondary metabolites, comprising the neurotoxin nicotine,3 trypsin protease inhibitors (TPIs) 4 and oxylipins,5 were shown to accumulate (see refs. 6 and 7, for review). Oxylipins are membrane fatty acid derivatives formed through the oxygenation of free or phospholipid-bound polyunsaturated fatty acids such as linoleic acid (18:2), linolenic acid (18:3), and roughanic acid (16:3).8-10 The final product of the so-called Vick and Zimmerman pathway driving oxylipin biosynthesis is (+)-7-with regard URAT1 inhibitor 1 to the URAT1 inhibitor 1 phenomenon of Rabbit Polyclonal to SOX8/9/17/18 arthropod deterrence that is observed when young-born seedlings grow underneath the soil or fallen leaves. Using biochemical and genetic tools, in combination with laboratory feeding experiments using 2 nocturnal isopod species, the apical hook was identified as JA-protected Achilles’ heel of etiolated plants that expressed high amounts of a Kunitz protease inhibitor (PI) presumably blocking digestive proteases of the isopod devourers. Because a similar correlation between JA production, Kunitz-PI accumulation and isopod resistance was observed for flowers/inflorescences, our data suggest a common pathway of COI1-dependent signaling that operates in seedlings and adult plants at quite defined stages of development. Results Creelman and Mullet21 identified and quantified JA over plant development and noticed high JA contents in the apical hook of etiolated seedlings. Because the apical hook contains the apical meristem, it must be protected against mechanical damage. One protection mechanism could be to express structural proteins that mechanically reinforce the apical hook and enclosed vascular bundles. In chickpea, 2 Kunitz protease inhibitors were identified of which one was proposed to accomplish such role in etiolated seedlings.22,23 We recently identified another Kunitz-PI, designated Kunitz-PI;1,24 that is expressed in the apical hook of etiolated Arabidopsis seedlings and asked whether its expression is under control of the JA biosynthesis and signaling pathways. To this end, JA-deficient seedlings of the allene oxide synthase (mutant 25,26 and JA-Ile-insensitive seedlings of the mutant27,28 were used. In addition to Kunitz-PI;1, we analyzed the expression of RESPONSIVE TO DESICCATION 21 (RD21)29,30 that has been demonstrated to sequester part of Kunitz-PI;1 in terms of higher molecular mass complexes in the apical hook of etiolated seedlings.24 RD21 is synthesized as a preproprotein bearing an NH2-terminal propeptide with auto-inhibitory activity and a COOH-terminal granulin-domain containing propeptide with unknown function.29,30 The NH2-terminal propeptide is removed by a yet unknown mechanism involving either autocatalytic processing under low pH or the activity of a processing enzyme.24,29,30 As a first type of experiments, we tested the expression of Kunitz-PI; 1 in the apical hook and URAT1 inhibitor 1 cotyledons of 4.5 d-old, etiolated Arabidopsis seedlings. After protein extraction and SDS-PAGE, Western blots were probed with Kunitz-PI;1 antibodies.31 As shown in Fig.?1, weak Kunitz-PI;1 signals were obtained for protein extracts from the apical hook of etiolated plants but no signals were URAT1 inhibitor 1 obtained with protein extracts from the cotyledons, consistent with previously reported URAT1 inhibitor 1 expression studies.24 Treatment of etiolated seedlings with JA triggered tremendous increases in Kunitz-PI;1 protein accumulation both in the apical hook and the cotyledons. By contrast, RD21 protein levels were reduced in seedlings treated with JA. As said before, RD21 has a quite complex biosynthetic pathway that comprises several processing steps and leads to an intermediate and mature form, designated iRD21 and mRD21, respectively.29,30 As judged from the size of the 2 2 RD21-crossreactive bands, both iRD21 and mRD21 accumulated in the cotyledons and apical hooks of etiolated seedlings. Remarkably, their accumulation was suppressed by exogenous JA (Fig.?1A and B). Open in a separate window Figure 1. Kunitz-PI;1 and RD21 protein expression in 4.5 d-old Arabidopsis seedlings that had been treated with MeJA or.