Differential fructan accumulation and expression of fructan biosynthesis, invertase and defense genes is induced in Agave tequilana plantlets by sucrose or stress-related elicitors

Abstract

The effect of short-term treatments with non-toxic concentrations of chemical elicitors of carbon mobilization and/or defense responses on fructan accumulation and complexity was analyzed in Agave tequilana plantlets. These included sucrose (ExSuc), salicylic acid (SA), and methyl jasmonate (MeJA). Methyl viologen (MV), an oxidative-stress elicitor, was also tested. Stems of ExSuc- and SA-treated agaves accumulated fructan with contrasting degree of polymerization (DP), being higher (DP12) in the ExSuc treatment. The difference agreed with 1-SST, 6G-FFT and 6-fructan exohydrolase (FEH) gene expression patterns. Thus, a strong, 6G-FFT expression detected 6 days after treatment (DAT), coupled to a systematic repression of FEH genes occurred in Ex-Suc treated agaves. Conversely, SA treatment induced maximum 6G-FFT expression and a transitory induction of FEH genes 2 DAT. MV also induced an accumulation of low-DP fructans 6 DAT. Additionally, it stimulated the highest fructan accumulation in leaves. Contrariwise, MeJA led to a depletion of soluble non-structural carbohydrates (NSCs) and fructan, particularly in leaves. An inverse relationship between high invertase and FEH gene expression levels and minimal NSCs and fructan reserves was observed in response to MeJA. Low DP fructan accumulation by MV could not be attributed to a measurable oxidative stress. Still, high antioxidant enzyme activity, indirectly manifesting oxidative stress, coincided with fructan accumulation in MV-treated agaves. High invertase and FEH expression levels induced by MeJA in leaves, and to a lesser degree by SA and MV, coincided with transcript accumulation of defense-related genes, and were, to a certain extent, in accordance with the “sweet immunity” concept, linking sugar and defense signaling.