December 2017, Volume 59 Issue 12, Pages 841每909.


Cover Caption: Stigmatic exudate in the Annonaceae
Stigmas in the early-divergent flowering plant family Annonaceae are covered with a sticky fluid when receptive. In this issue, Lau et al. (pp. 881每894) investigate alternative functional explanations for this exudate, demonstrating three parallel roles: as sugar-rich reward for beetle pollinators; providing optimal conditions for pollen hydration and germination; and as a medium to allow intercarpellary growth of pollen tubes.

 

          Letter to the Editor
NaMYB8 regulates distinct, optimally distributed herbivore defense traits  
Author: Martin Schäfer, Christoph Brütting, Shuqing Xu, Zhihao Ling, Anke Steppuhn, Ian T. Baldwin and Meredith C. Schuman
Journal of Integrative Plant Biology 2017 59(12): 844每850
Published Online: August 26, 2017
DOI: 10.1111/jipb.12593
      
    

When herbivores attack, plants specifically reconfigure their metabolism. Herbivory on the wild tobacco Nicotiana attenuata strongly induces the R2R3 MYB transcriptional activator MYB8, which was reported to specifically regulate the accumulation of phenolamides (PAs). We discovered that transcriptional regulation of trypsin protease inhibitors (TPIs) and a threonine deaminase (TD) also depend on MYB8 expression. Induced distributions of PAs, TD and TPIs all meet predictions of optimal defense theory: their leaf concentrations increase with the fitness value and the probability of attack of the tissue. Therefore, we suggest that these defensive compounds have evolved to be co-regulated by MYB8.

Abstract (Browse 320)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Tissues contributing most to plant fitness, such as younger leaves and flowers, are often the best defended: a prediction of optimal defense theory (OD). The mechanisms determining optimal distributions are poorly understood. We show that a MYB transcription factor co-regulates biosynthetically unrelated defenses which share an optimal distribution.
          Cell and Developmental Biology
Arabidopsis EXO70A1 recruits Patellin3 to the cell membrane independent of its role as an exocyst subunit  
Author: Chengyun Wu, Lu Tan, Max van Hooren, Xiaoyun Tan, Feng Liu, Yan Li, Yanxue Zhao, Bingxuan Li, Qingchen Rui, Teun Munnik and Yiqun Bao
Journal of Integrative Plant Biology 2017 59(12): 851每865
Published Online: August 16, 2017
DOI: 10.1111/jipb.12578
      
    

The exocyst is a well-known complex which tethers vesicles at the cell membrane before fusion. Whether an individual subunit can execute a unique function is largely unknown. Using yeast-two-hybrid (Y2H) analysis, we found that EXO70A1 interacted with the GOLD domain of Patellin3 (PATL3). The direct EXO70A1-PATL3 interaction was supported by in vitro and in vivo experiments. In Arabidopsis, PATL3-GFP colocalized with EXO70A1 predominantly at the cell membrane, and PATL3 localization was insensitive to BFA and TryA23. Remarkably, in the exo70a1 mutant, PATL3 proteins accumulated as punctate structures within the cytosol, which did not colocalize with several endomembrane compartment markers, and was insensitive to BFA. Furthermore, PATL3 localization was not changed in the exo70e2, PRsec6 or exo84b mutants. These data suggested that EXO70A1, but not other exocyst subunits, was responsible for PATL3 localization, which is independent of its role in secretory/recycling vesicle-tethering/fusion. Both EXO70A1 and PATL3 were shown to bind PI4P and PI(4,5)P2 in vitro. Evidence was obtained that the other four members of the PATL family bound to EXO70A1 as well, and shared a similar localization pattern as PATL3. These findings offered new insights into exocyst subunit-specific function, and provided data and tools for further characterization of PATL family proteins.

Abstract (Browse 849)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The octameric exocyst complex is thought to act as a whole to tether vesicles before fusion. In this study, exocyst subunit EXO70A1 was found to play a unique role in recruiting cytosolic PATL3 onto the cell membrane, independent of the conventional role of the exocyst in secretory/recycling vesicle-tethering.
          Functional Omics and Systems Biology
Genetic dissection of top three leaf traits in rice using progenies from a japonica ℅ indica cross
Author: Changbin Yin, Huihui Li, Zhigang Zhao, Zhiquan Wang, Shijia Liu, Liangming Chen, Xi Liu, Yunlu Tian, Juan Ma, Lidong Xu, Dashuang Zhang, Susong Zhu, Danting Li, Jianmin Wan and Jiankang Wang
Journal of Integrative Plant Biology 2017 59(12): 866每880
Published Online: September 6, 2017
DOI: 10.1111/jipb.12597
      
    

The size of the top three leaves of rice plants is strongly associated with yield; thus, it is important to consider quantitative traits representing leaf size (e.g., length and width) when breeding novel rice varieties. It is challenging to measure such traits on a large scale in the field, and little is known about the genetic factors that determine the size of the top three leaves. In the present study, a population of recombinant inbred lines (RILs) and reciprocal single chromosomal segment substitution lines (SSSLs) derived from the progeny of a japonica Asominori × indica IR24 cross were grown under four diverse environmental conditions. Six morphological traits associated with leaf size were measured, namely length and flag leaf, length and flag, second and third leaves. In the RIL population, 49 QTLs were identified that clustered in 30 genomic region. Twenty-three of these QTLs were confirmed in the SSSL population. A comparison with previously reported genes/QTLs revealed eight novel genomic regions that contained uncharacterized ORFs associated with leaf size. The QTLs identified in this study can be used for marker-assisted breeding and for fine mapping of novel genetic elements controlling leaf size in rice.

Abstract (Browse 307)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Top three leaves in rice determine plant type and grain yield. Using one japonica℅indica cross, we identified 30 genomic regions and then confirmed 23 of them affecting length and width of the top three leaves. Compared with length, width is more correlated with each other, sharing more common genes.
          Molecular Ecology and Evolution
Stigmatic exudate in the Annonaceae: Pollinator reward, pollen germination medium or extragynoecial compitum?  
Author: Jenny Y. Y. Lau, Chun-Chiu Pang, Lawrence Ramsden and Richard M.K. Saunders
Journal of Integrative Plant Biology 2017 59(12): 881每894
Published Online: September 6, 2017
DOI: 10.1111/jipb.12598
      
    

Although “dry-type” stigmas are widely regarded as ancestral in angiosperms, the early-divergent family Annonaceae has copious stigmatic exudate. We evaluate three putative functions for this exudate: as a nutritive reward for pollinators; as a pollen germination medium; and as an extragynoecial compitum that enables pollen tube growth between carpels. Stigmatic exudate is fructose dominated (72.2%), but with high levels of glucose and sucrose; the dominance of hexose sugars and the diversity of amino acids observed, including many that are essential for insects, support a nutritive role for pollinators. Sugar concentration in pre-receptive flowers is high (28.2%), falling during the peak period of stigmatic receptivity (17.4%), and then rising again toward the end of the pistillate phase (32.9%). Pollen germination was highest in sugar concentrations <20%. Sugar concentrations during the peak pistillate phase therefore provide optimal osmolarity for pollen hydration and germination; subsequent changes in sugar concentration during anthesis reinforce protogyny (in which carpels mature before stamens), enabling the retention of concentrated exudate into the staminate phase as a pollinator food reward without the possibility of pollen germination. Intercarpellary growth of pollen tubes was confirmed: the exudate therefore also functions as a suprastylar extragynoecial compitum, overcoming the limitations of apocarpy.

Abstract (Browse 285)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Unlike most early-divergent flowering plants, Annonaceae species produce copious stigmatic fluid when receptive. We investigated the role of this exudate, and provided evidence to support three functions: as a food reward for pollinators; as a pollen germination medium; and as a medium that allows pollen tube growth between separate carpels.
          Molecular Physiology
Potassium channel AKT1 is involved in the auxin-mediated root growth inhibition in Arabidopsis response to low K+ stress  
Author: Juan Li, Wei-Hua Wu and Yi Wang
Journal of Integrative Plant Biology 2017 59(12): 895每909
Published Online: August 7, 2017
DOI: 10.1111/jipb.12575
      
    

The changes in external K+ concentration affect plant root growth. However, the molecular mechanism for perceiving a K+ signal to modulate root growth remains unknown. It is hypothesized that the K+ channel AKT1 is involved in low K+ sensing in the Arabidopsis root and subsequent regulation of root growth. Along with the decline of external K+ concentration, the primary root growth of wild-type plants was gradually inhibited. However, the primary root of the akt1 mutant could still grow under low K+ (LK) conditions. Application of NAA inhibited akt1 root growth, but promoted wild-type root growth under LK conditions. By using the ProDR5:GFP and ProPIN1:PIN1-GFP lines, we found that LK treatment reduced auxin accumulation in wild-type root tips by degrading PIN1 proteins, which did not occur in the akt1 mutant. The LK-induced PIN1 degradation may be due to the inhibition of vesicle trafficking of PIN1 proteins. In conclusion, our findings indicate that AKT1 is required for an Arabidopsis response to changes in external K+, and subsequent regulation of K+-dependent root growth by modulating PIN1 degradation and auxin redistribution in the root.

Abstract (Browse 885)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
AKT1 is an important K+ channel that mediates K+ uptake in Arabidopsis root. Here, we demonstrated that AKT1 plays an essential role in Arabidopsis response to low K+ stress. AKT1 can perceive external K+ concentration and subsequently regulate primary root growth by modulating PIN1 degradation and auxin redistribution.
 
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