Abstract
Abscisic acid (ABA) plays an important role in plant adaptation to water deficits, but its role in regulating root growth (primary root elongation and lateral root number) during different drought-phases remains unclear. Here, we exposed wild-type (WT) and ABA-deficient (not) tomato plants to three continuous drought-phases (moderate drying: day 0–21; severe drying: day 22–47 and re-watering: day 48–51). It was found that WT increased primary root growth during moderate drying; maintained more lateral roots, and greater primary root and total root length under severe drying; and produced more roots after re-watering. After RNA-Seq analysis, we found that the auxin-related genes in root showed different expression patterns between WT and not under drying or re-watering. Further, exogenous supply of IAA partially recovered the root growth of ABA-deficient not plants under three continuous drought-phases. Our results suggested that ABA regulation of tomato root growth during soil drying and recovery can involve auxin response.