During stress as plants cannot move, they have evolved signals at the cellular, transcriptomic or metabolic level to counteract or combat stress. Although there are many chemical methods to protect plants from stress, the use of beneficial microorganisms is an environmentally friendly approach. In this thesis I used a beneficial Fusarium strain, Fusarium incarnatum K23, to help plants combat salt stress. K23 colonized the whole tomato seedlings and acted via different mechanisms. At the cellular level, calcium signaling experiments showed that K23 requires the poly(A)-specific ribonuclase AtPARN but not malectin domain-containing cellooligomer receptor kinase1 CORK1 for calcium elevation and activation of calcium-dependent downstream responses., whereas well-studied endophytic fungi such as Piriformospora indica require both AtPARN and CORK1 for calcium elevation. At the hormone level, GA was the most prominently upregulated hormone, others being IAA and SA. At the transcriptomic level, it is known that K23 mainly regulates WRKY, MYB and DREB genes. Since K23 produces GA, the genes GA-20 oxidase and gibberellin-3-beta-di-oxygenase are also upregulated in the plant. The increased GA concentration in the plant probably explains the morphophysiological changes such as increased root and shoot weights in the tomato seedlings. Colonization of unstressed tomato seedlings with K23 causes only moderate changes in gene expression, whereas the fungus reprograms the expression pattern in salt-exposed tomato seedlings to a considerable extent. K23 colonization of salt-exposed tomato seedlings also led to an altered metabolite profile. The present study shows that K23 induces cellular, morphological, transcriptomic, hormonal and metabolic changes in salt-exposed tomato seedlings. The resulting improved growth of seedlings under salt stress could be of importance for agricultural applications.
Priya Reddy (Wed,) studied this question.