|Siddappaji, Madhura - University Of Illinois|
|Krishnankutty, Sindhu - University Of Illinois|
|Calla Zalles, Bernarda|
|Paige, Ken - University Of Illinois|
Submitted to: Biomed Central (BMC) Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2015
Publication Date: 11/16/2015
Citation: Siddappaji, M.H., Krishnankutty, S.M., Calla Zalles, B., Clough, S.J., Paige, K.N. 2015. The role of invertases in plant compensatory responses to simulated herbivory. Biomed Central (BMC) Plant Biology. 15:278.
Interpretive Summary: Some plant species benefit from being eaten by herbivores as this feeding removes the growing point and triggers increased new growth. This new growth can even overcompensate, leading to greater yield from damaged plants than from undamged plants. Although there is evidence that genetic variation for overcompensation exists, little is known about the molecular mechanisms leading to enhanced growth and reproduction following herbivore damage. We identified a family of genes encoding enzymes that are involved in the overcompensation response. This class of enzymes (invertases) is involved in sugar metabolism that provides important inputs into a biochemical pathway that is central to plant survival. The expression of genes controlling the invertase enzymes differed between plants that do or do not show overcompensation. The function of these enzymes makes it possible that they could play a significant role in the increase growth observed in the overcompensating plants. The results also suggest that increased invertase activity earlier in the life of the plant would facilitate flower and fruit development. Gaining an understanding of the genetic basis of overcompensation could be of great interest to plant breeders who might use this trait to improve seed yield. From an evolutionary perspective, this study represents an important contribution where we have clearly demonstrated the genetic basis of a plant response to changing environmental conditions.
Technical Abstract: The ability of a plant to recover from mammalian herbivory by exhibiting enhanced growth and reproduction compared to unharmed plants, is called compensation. Although it is clear that genetic variation for compensation exists, little is known about the specific genes underpinnings leading this fitness response. One compensation associated gene was identified in Arabidopsis thaliana to encode glucose-6-phosphate-1-dehydrogenase (Siddappaji et al. 2013). Here we determined the importance of another Arabidopsis gene family associated with the compensatory response, genes encoding invertase isoenzymes, a class of enzymes that shunt glucose to activate the oxidative pentose phosphate pathway. To gain insight into the role of invertase genes, we used a suite of expression assays over developmental time. Arabidopsis ecotypes Columbia and Landsberg erecta (overcompensating and undercompensating genotypes, respectively), as well as invertase knockout mutants, were used for these studies. The expression of invertases following the removal of apical dominance varied in these genotypes. Columbia, an overcompensating genotype, showed that nine of twelve invertase isoenzymes were significantly up-regulated one to five days after the removal of apical dominance, whereas Landsberg erecta, an undercompensating genotype, showed only a significant decline in two neutral invertases at 15 days post-clipping. These results were consistent with the patterns observed for G6PDH1, showing up-regulation at five days post-clipping in Columbia, possibly due, in part, to an increase in glucose fed from invertase isoenzymes into the oxidative pentose phosphate pathway, facilitating the rapid regrowth and greater biomass accumulation observed in the overcompensating genotype Columbia. Furthermore, there was a general trend toward higher expression at 50% flowering for both clipped and unclipped plants (with no significant differences in expression between treatments or between genotypes) in six of twelve Columbia invertase isoenzymes, and three of twelve for Landsberg erecta. These results suggest that Columbia, and to a lesser degree Landsberg erecta, may up-regulate gene expression over earlier time periods in order to facilitate flower and fruit development. These results are also consistent with the patterns observed for G6PDH1, showing greater up-regulation at 50% flowering post-clipping in Columbia (i.e., twice the number of invertases up-regulating to supply the added glucose for increased flower and fruit production in the overcompensating genotype, Columbia versus the undercompensating genotype, Landsberg erecta). The T-DNA knockout experiments on the two invertase genes, a vacuolar invertase and a neutral invertase, confirm their importance in plant growth and fitness in Arabidopsis thaliana following the removal of apical dominance. Of particular note, there does not appear to be any functional redundancy of other invertases or sucrose synthases. Thus, all of these enzymes appear to be necessary for normal growth, development and reproduction and, most importantly here, for growth and fitness compensation following apical damage.