Arabidopsis trehalose phosphate synthaseII (tpsII) mutants are ABA-hypersensitive during early development while tps7 to tps11 show increased drought susceptibility consistent with anomalous stomatal closure and weak post-stress recovery responses

The biological function of TREHALOSE PHOSPHATE SYNTHASE II (TPSII) genes remains largely unknown, although experimental evidence has shown that they may contribute to regulate plant stress responses and plant development. The results of the present study show that most of the Arabidopsis thaliana insertional tpsII mutants tested were highly susceptible to severe water deficit stress (WDS), a trait particularly noticeable in the tps7.2 mutant. WDS susceptibility in this mutant was consistent with a reduced stomatal closure response, a strong reduction of branched amino acids during WDS and a weak metabolic recovery after rewatering. An augmented nitrate reductase activity levels detected during the WDS-recovery phase in this and other tpsII mutants could have been an additional contributing factor to WDS susceptibility, altered stomatal closure and reduced germination and seedling growth. Besides, most tpsII mutants had reduced seed germination, shorter root lengths and smaller root areas that were further diminished by exogenous ABA. Conversely, increased sensitivity to 100 mM trehalose, measured as root length in vitro, was greater in the tps5.2 and tps6.1 mutants, who were also WDS-tolerant. The results obtained in the present study, suggest that specific TPSII proteins may interact with the TPS1-Tre6P-SnRK1 central metabolic regulator system in A. thaliana to control WDS and early plant development through different mechanisms that are discussed further. However, the mean(s) by which these TPS II proteins may control TPSI activity and/or Tre6P levels remain(s) to be determined.