Deficiency in a Very-Long-Chain Fatty Acid β-Ketoacyl-Coenzyme A Synthase of Tomato Impairs Microgametogenesis and Causes Floral Organ Fusion  

Abstract

Previously, it was shown that β-ketoacyl-coenzyme A synthase ECERIFERUM6 (CER6) is necessary for the biosynthesis of very-long-chain fatty acids with chain lengths beyond C₂₈ in tomato (Solanum lycopersicum) fruits and C₂₆ in Arabidopsis (Arabidopsis thaliana) leaves and the pollen coat. CER6 loss of function in Arabidopsis resulted in conditional male sterility, since pollen coat lipids are responsible for contact-mediated pollen hydration. In tomato, on the contrary, pollen hydration does not rely on pollen coat lipids. Nevertheless, mutation in SlCER6 impairs fertility and floral morphology. Here, the contribution of SlCER6 to the sexual reproduction and flower development of tomato was addressed. Cytological analysis and cross-pollination experiments revealed that the slcer6 mutant has male sterility caused by (1) hampered pollen dispersal and (2) abnormal tapetum development. SlCER6 loss of function provokes a decrease of n- and iso-alkanes with chain lengths of C₂₇ or greater and of anteiso-alkanes with chain lengths of C₂₈ or greater in flower cuticular waxes, but it has no impact on flower cuticle ultrastructure and cutin content. Expression analysis confirmed high transcription levels of SlCER6 in the anther and the petal, preferentially in sites subject to epidermal fusion. Hence, wax deficiency was proposed to be the primary reason for the flower fusion phenomenon in tomato. The SlCER6 substrate specificity was revisited. It might be involved in elongation of not only linear but also branched very-long-chain fatty acids, leading to production of the corresponding alkanes. SlCER6 implements a function in the sexual reproduction of tomato that is different from the one in Arabidopsis: SlCER6 is essential for the regulation of timely tapetum degradation and, consequently, microgametogenesis.

Analyses of Tomato Fruit Brightness Mutants Uncover Both Cutin-Deficient and Cutin-Abundant Mutants and a New Hypomorphic Allele of GDSL Lipase

“…Similar observations have been made in maize (Zea mays) and in rice (Oryza sativa) (Jenks et al, 2002;Islam et al, 2009). In addition, no organ fusion was observed among all the glossy/dull fruit mutants studied, in contrast with the glossy mutants described in Arabidopsis or the SlCER6 loss-offunction wax tomato mutant (Smirnova et al, 2013). Although the participation of wax in the glossy aspect of the fruit cannot be excluded (several glossy mutants display significant increases in wax load), our results strengthen the conclusion that the glossy/dull fruit appearance in our tomato mutants is not due to wax deficiency.…”

Arabidopsis HSP70‐16 is required for flower opening under normal or mild heat stress temperatures

“…Previous studies have shown that a defective cuticle often causes postgenital fusion (Kurdyukov et al, ; Shi et al, ; Smirnova et al, ). To test whether loss of function of HSP70‐16 changes cuticle properties and chemical profiles in floral organs, we performed floral organ surface characterization using SEM and TEM and sepal wax and cutin composition assays using GC‐MS and GC‐FID.…”

The Formation and Function of Plant Cuticles

“…This phenomenon has been observed in a wax-deficient tomato mutant (Smirnova et al, 2013), a range of Arabidopsis mutants with abnormal cuticles (Yephremov et al, 1999;Wellesen et al, 2001;Kurdyukov et al, 2006a;Bird et al, 2007), and transgenic Arabidopsis plants overexpressing a secreted fungal cutinase (Sieber et al, 2000). The fusion zones are often marked by two adjacent polysaccharide cell walls with no visible cuticle separating the two organs, although the fused epidermal layers maintain their identity, as indicated by the differentiation of internal nonfunctional stomata within fusion zones (Sieber et al, 2000).…”