Negative Regulation of Age-Related Developmental Leaf Senescence by the IAOx Pathway, PEN1, and PEN3.

Renee A Crane,Nelly Castaneda,Wenwen Kong,Charidan L Jackson,Marielle Cardénas Valdez,Islam Mostafa,Sixue Chen,Judy A Brusslan,Ciairra J Riley,Shweta Chhajed

doi:10.3389/fpls.2019.01202

Abstract

Early age-related developmental senescence was observed in Arabidopsis cyp79B2/cyp79B3 double mutants that cannot produce indole-3-acetaldoxime (IAOx), the precursor to indole glucosinolates (IGs), camalexin and auxin. The early senescence phenotype was not observed when senescence was induced by darkness. The cyp79B2/cyp79B3 mutants had lower auxin levels, but did not display auxin-deficient phenotypes. Camalexin biosynthesis mutants senesced normally; however, IG transport and exosome-related pen1/pen3 double mutants displayed early senescence. The early senescence in pen1/pen3 mutants depended on salicylic acid and was not observed in pen1 or pen3 single mutants. Quantitation of IGs showed reduced levels in cyp79B2/cyp79B3 mutants, but unchanged levels in pen1/pen3, even though both of these double mutants display early senescence. We discuss how these genetic data provide evidence that IAOx metabolites are playing a protective role in leaf senescence that is dependent on proper trafficking by PEN1 and PEN3, perhaps via the formation of exosomes.

Highlights

Meristems continuously produce new organs, but most plants cannot sustain all these tissues
We propose that IAOx metabolite(s), which rely on PEN1 and PEN3 for correct localization, are playing a protective role during leaf senescence
IAOx Biosynthesis Mutants Display Early, Accelerated Leaf Senescence and Reduced Fitness cyp79B2/cyp79B3 double mutants were constructed from single T-DNA insertion lines (Supplemental Figure 2)

Summary

Introduction

Meristems continuously produce new organs, but most plants cannot sustain all these tissues. Optimal transport of nutrients is essential for reproductive success; early senescence, often induced by abiotic stress, will result in inefficient transport of nutrients while late senescence can either increase yield or result in reduced nutrient transport likely due to increased leaf sink strength (Smart, 1994; Tollenaar and Wu, 1999; Ding et al, 2005; Derkx et al, 2012) Numerous hormones, such as ethylene (Li et al, 2013), jasmonic acid (JA) (He et al, 2002), and salicylic acid (SA) (Morris et al, 2003), promote both defense responses and senescence (Guo and Gan, 2012; Jibran et al, 2013). The sole well-established phytohormone negative regulator of leaf senescence is cytokinin (Gan and Amasino, 1995; Kusaba et al, 2013)

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