Understanding the Role of Defective Invertases in Plants: Tobacco Nin88 Fails to Degrade Sucrose1[W]

• Published in: Plant physiology (Bethesda) Vol. 161; no. 4; pp. 1670 - 1681
• Main Authors: Le Roy, Katrien, Vergauwen, Rudy, Struyf, Tom, Yuan, Shuguang, Lammens, Willem, Mátrai, Janka, De Maeyer, Marc, Van den Ende, Wim
• Format: Journal Article
• Language: English
• Published: American Society of Plant Biologists 27-02-2013
• Subjects: Biochemistry and Metabolism
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.112.209460

An inactive invertase may indirectly stimulate the activity of active cell wall invertases.
Cell wall invertases (
cwINVs
), with a high affinity for the cell wall, are fundamental enzymes in the control of plant growth, development, and carbon partitioning. Most interestingly, defective
cwINVs
have been described in several plant species. Their highly attenuated sucrose (Suc)-hydrolyzing capacity is due to the absence of aspartate-239 (Asp-239) and tryptophan-47 (Trp-47) homologs, crucial players for stable binding in the active site and subsequent hydrolysis. However, so far, the precise roles of such defective
cwINVs
remain unclear. In this paper, we report on the functional characterization of tobacco (
Nicotiana tabacum
) Nin88, a presumed fully active
cwINV
playing a crucial role during pollen development. It is demonstrated here that Nin88, lacking both Asp-239 and Trp-47 homologs, has no invertase activity. This was further supported by modeling studies and site-directed mutagenesis experiments, introducing both Asp-239 and Trp-47 homologs, leading to an enzyme with a distinct Suc-hydrolyzing capacity. In vitro experiments suggest that the addition of Nin88 counteracts the unproductive and rather aspecific binding of tobacco cwINV1 to the wall, leading to higher activities in the presence of Suc and a more efficient interaction with its cell wall inhibitor. A working model is presented based on these findings, allowing speculation on the putative role of Nin88 in muro. The results presented in this work are an important first step toward unraveling the specific roles of plant defective
cwINVs
.