Single-Gene Overexpression of Pigeon Pea (Cajanus cajan) CcSBPase or CcSHMT1 and Multigene Overexpression of CcSBPase with CcSTN7 Do Not Impact Physiological Responses to Water Deficit Stress in Tobacco (Nicotiana tabacum)

Drought stress is one of the environmental stress factors exacerbated by climate change. It causes water deficit stress, leading to economic yield losses. Its impact is largely felt in semi-arid and arid regions, often occupied by resource-limited farmers. This study aimed to determine whether transgenic tobacco plants improved for photosynthesis performance to enhance plant yield perform better than wild-type (WT) untransformed plants under induced water deficit stress conditions. In doing so, transgenic tobacco (Nicotiana tabacum) plants with genes that encode sedoheptulose-1,7-bisphosphatase (SBPase), serine/threonine protein kinase-7 (STN7), and serine hydroxymethyltransferase-1 (SHMT1) enzymes from pigeon pea (Cajanus cajan) were exposed to water deficit stress by withholding water for 15 days. The transgenic lines used were composed of single-gene T3 transgenic lines and F2 generation multigene overexpressing lines. To determine the response to water deficit stress, specific physiological parameters were recorded on days 0, 8, and 15 of withholding water supply. These parameters included leaf relative water content (RWC), chlorophyll fluorescence (Fv/Fm), and stomatal conductance, accompanied by daily growth substrate moisture measurements (soil moisture). The results show a decline in photosynthesis in WT and all transgenic lines, suggesting that there is no improvement in tolerance to water deficit stress. This is observed through the decline in stomatal conductance and Fv/Fm from day 8 to 15 after withholding the water supply. Based on these observations, we conclude that the overexpression of pigeon pea SBPase and SHMT1, as well as the simultaneous overexpression of SBPase with STN7, do not improve physiological responses to induced water deficit stress in the tobacco model plant.