Drought stress-induced irregularities in male organ development cause
stage-specific morpho-physiological and transcriptome changes in tomato
Abstract
Drought limits the growth and productivity of plants. Reproductive
development is sensitive to drought but the underlying physiological and
molecular mechanisms remain unclear in tomato. Here, we investigated
drought effect on tomato floral development using morpho-physiological
and transcriptome analyses. Drought induced bud and flower abortions,
and reduced fruit set/yield, triggered by male sterility due to abnormal
anther and pollen development. Under drought stress (DS), anthers at
pollen mother cell to meiotic (PMC-MEI) stage survived while anthers at
tetrad to uninucleate microspore (TED-VUM) stage aborted. PMC-MEI stage
had lower ABA increase, reduced IAA and higher sugar contents under DS
relative to well-watered. However, TED-VUM stage had higher ABA
increase, higher IAA level and no accumulation of soluble sugars,
indicating abnormal carbohydrate and hormone metabolisms. Moreover,
RNA-Seq analysis identified altogether ˃15,000 differentially expressed
genes that were assigned to multiple pathways, suggesting tomato anthers
utilize complicated mechanisms to cope with drought. Major genes
involved in tapetum/microspore development and ABA homeostasis were
drought-induced while those involved in sugar utilization and IAA
metabolism were repressed at PMC-MEI stage. Our results suggest
crosstalks between phytohormones and carbohydrate metabolism at
different anther stages under DS and provide novel insight into
molecular mechanisms of drought tolerance in tomato.