| Summary: | Tomato is one of the most widely consumed horticultural products. However, tomato is very sensitive to changes in temperature. Daily average temperatures above 32 °C severely reduced tomato plant growth, development, and productivity. Therefore, climate change-induced global warming is a major threat to future tomato production. Good photosynthetic capability under heat stress conditions is known to be a major sign of heat tolerance. Tomato <i>INDOLE-ACETIC-ACID (SlIAA9</i>) is a transcriptional repressor in auxin signaling. <i>SlIAA9</i> mutation caused heightened endogenous auxin response and biosynthesis within plant tissues. In this study, we studied the photosynthetic capability of <i>iaa9-3</i> and <i>iaa9-5</i> mutants under heat-stress conditions. We discovered that both <i>iaa9-3</i> and <i>iaa9-5</i> could maintain their photosynthetic capability after 14 days of heat treatment (>40 °C), differing from Wild Type-Micro-Tom (WT-MT) tomato. Both <i>iaa9</i> mutants had higher net photosynthetic rate, stomatal conductance, leaf total chlorophyll, leaf carotenoids, Fv/Fm value, and lower leaf MDA than WT-MT. These results suggested that the <i>SlIAA9</i> mutation benefits plant adaptation to heat stress.
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