ABA collaborates with lignin and flavonoid to improve pre-silking drought tolerance by tuning stem elongation and ear development in maize (Zea mays L.).

Drought is a major abiotic stress reducing maize yield worldwide especially before and during silking. The mechanism underlying drought tolerance in maize has not been elucidated especially from the perspective of different organs. Hence, we conducted field trials under pre-silking drought using two maize genotypes, FM985 (drought tolerant) and ZD958 (drought sensitive). The two genotypes did not differ in plant height, grain number, and yield under control. However, grain number per ear and yield of FM985 were 38.1% and 35.1% higher and plant height was 17.6% shorter than ZD958 under drought. More 13 C-photosynthates were transported to the ear in FM985 than in ZD958, which increased floret fertility and grain number. The number of differentially expressed genes were greatly higher in stem than in other organs. Stem-ear interactions are key determinants of drought tolerance, in which genes expression related to ABA, lignin and flavonoid biosynthesis, and carbon metabolism in the stem were induced by drought, which inhibited stem elongation and promoted assimilates allocation to the ear in FM985. In comparison with ZD958, the activities of trehalose-6-phosphate phosphatase and sucrose non-fermentation-associated kinase 1 were higher in the stem and lower in the kernel of FM958, which facilitated kernel formation. These results reveal that, beyond ear response, stem elongation is involved in the whole process of drought tolerance before silking. ABA together with T6P, lignin and flavonoid suppresses stem elongation and allocates assimilate into ear, providing a novel and systematic regulatory pathway for drought tolerance in maize.