Contents 362I.362II.363III.366IV.369V.371VI.372373References373 Summary Plants master the art of coping with environmental challenges in two ways: on the one hand, through their extensive defense systems, and on the other, by their developmental plasticity. The plant hormone auxin plays an important role in a plant's adaptations to its surroundings, as it specifies organ orientation and positioning by regulating cell growth and division in response to internal and external signals. Important in auxin action is the family of PIN‐FORMED (PIN) auxin transport proteins that generate auxin maxima and minima by driving polar cell‐to‐cell transport of auxin through their asymmetric subcellular distribution. Here, we review how regulatory proteins, the cytoskeleton, and membrane trafficking affect PIN expression and localization. Transcriptional regulation of PIN genes alters protein abundance, provides tissue‐specific expression, and enables feedback based on auxin concentrations and crosstalk with other hormones. Post‐transcriptional modification, for example by PIN phosphorylation or ubiquitination, provides regulation through protein trafficking and degradation, changing the direction and quantity of the auxin flow. Several plant hormones affect PIN abundance, resulting in another means of crosstalk between auxin and these hormones. In conclusion, PIN proteins are instrumental in directing plant developmental responses to environmental and endogenous signals.

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The Nicotiana plumbaginifolia gnl gene encoding a 8-1,3-glucanase isoform has been characterired. The gnl product represents an isoform distinct from the previously identified tobacco 8-1,3-glucanases. By expressing gnl in Escherichia coli, we have determined directly that the encoded protein does, indeed, correspond to a &1,3-glucanase. In N. plumbaginifolia, gnl was found to be expressed in roots and older leaves. Transgenic tobacco plants containing the 5'-noncoding region of gnl fused to the 8-glucuronidase (GUS) repotter gene also showed maximum levels of GUS activity in roots and older leaves. No detectable activity was present in the upper part of the transgenic plants with the exception of stem cells at the bases of emerging shoots. The expression conferred by the gnl promoter was differentially induced in response to specific plant stress treatments. Studies of three plant-bacteria interactions showed high levels of GUS activity when infection resulted in a hypersensitive reaction. lncreased gene expression was confined to cells surrounding the necrotic lesions. The observed expression pattern suggests that the characterized ,í3-1,3-glucanase plays a role both in plant development and in the defense response against pathogen infection.

BackgroundParthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set. Previously, we identified several C. annuum genotypes that already show a certain level of parthenocarpy, and the seedless fruits obtained from these genotypes often contain carpel-like structures. In the Arabidopsis bel1 mutant ovule integuments are transformed into carpels, and we therefore carefully studied ovule development in C. annuum and correlated aberrant ovule development and carpelloid transformation with parthenocarpic fruit set.ResultsWe identified several additional C. annuum genotypes with a certain level of parthenocarpy, and confirmed a positive correlation between parthenocarpic potential and the development of carpelloid structures. Investigations into the source of these carpel-like structures showed that while the majority of the ovules in C. annuum gynoecia are unitegmic and anatropous, several abnormal ovules were observed, abundant at the top and base of the placenta, with altered integument growth. Abnormal ovule primordia arose from the placenta and most likely transformed into carpelloid structures in analogy to the Arabidopsis bel1 mutant. When pollination was present fruit weight was positively correlated with seed number, but in the absence of seeds, fruit weight proportionally increased with the carpelloid mass and number. Capsicum genotypes with high parthenocarpic potential always showed stronger carpelloid development. The parthenocarpic potential appeared to be controlled by a single recessive gene, but no variation in coding sequence was observed in a candidate gene CaARF8.ConclusionsOur results suggest that in the absence of fertilization most C. annuum genotypes, have parthenocarpic potential and carpelloid growth, which can substitute developing seeds in promoting fruit development.

The natural auxin indole-3-acetic acid is the first hormone identified in plants, and since it plays such a central role in plant growth and development, auxin has been the subject of intensive studies. A central question has been how the auxin signal is perceived by plant cells. The earliest experiments showed the presence of auxin binding particles at the plasma membrane (PM) and in the endoplasmic reticulum (ER) (Hertel et al., 1972). Screens for PM-localized auxin binding activities have led to the photo-affinity labeling and purification of Auxin Binding Protein 1 (ABP1) from maize coleoptile cells (Lö bler and Klä mbt, 1985). Despite observations in different laboratories that ABP1 localized to the PM where it seemed to mediate rapid electrophysiological and cell physiological responses to auxin, the auxin community remained skeptical about the role of ABP1 as auxin receptor for a long time, in part because of its predominant localization in the ER (reviewed by Napier et al., 2002). At some point, ABP1 was even jokingly referred to as a potential red herring in the search for the auxin receptor (Venis, 1995). However, after the first Arabidopsis abp1-1 loss-of-function allele pointed to a key role for ABP1 in cell elongation and division, the auxin community has adopted this abundantly expressed 22-kDa protein as extracellular auxin receptor (reviewed by Napier et al., 2002). Especially in recent years, the role of ABP1 in development has become more firmly established, in part as modulator of clathrinmediated endocytosis and microtubule orientation through its action on the Rho of Plants (ROP) family of GTPases (Robert et al., 2010;Chen et al., 2012Chen et al., , 2014 but also as regulator of auxin-responsive gene expression (Tromas et al., 2013). Recent evidence that auxin-bound ABP1 docks on the extracellular domain of the TRANSMEMBRANE KINASE1 (TMK1) finally linked its apoplastic localization to signaling by the PMassociated ROPs. TMK1 belongs to a small subfamily of four leucine-rich-repeat receptor-like kinases and the quadruple tmk1234 loss-of-function mutant shows several auxin-related phenotypes (Dai et al., 2013;Xu et al., 2014). In addition, auxin-mediated activation of ROP2 and ROP6 and the downstream effects on the actin and microtubule cytoskeleton, respectively, are largely abolished in this mutant (Xu et al., 2014;Grones and Friml, 2015).