Growth rate rather than growth duration drives growth heterosis in maize B104 hybrids

• Published in: Plant, cell and environment Vol. 41; no. 2; pp. 374 - 382
• Main Authors: Feys, Kim, Demuynck, Kirin, De Block, Jolien, Bisht, Anchal, De Vliegher, Alex, Inzé, Dirk, Nelissen, Hilde
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.02.2018; John Wiley and Sons Inc
• Subjects: Corn; Ectopic expression; Elongation; Environmental assessment; Flowering; Flowers; GA20‐oxidase; Growth rate; Heterosis; Hybrid Vigor - physiology; Hybrids; Inbreeding; Kernels; leaf growth; Leaves; Light emitting diodes; maize; Original; plant biotechnology; Plant Breeding; Plant Leaves - growth & development; Plants, Genetically Modified; PLASTOCHRON1; Transgenes; Zea mays - genetics; Zea mays - growth & development; heterosis; PLASTOCHRON1; leaf growth; plant biotechnology; GA20-oxidase; maize
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.13099

Research in maize is often performed using inbred lines that can be readily transformed, such as B104. However, because the B104 line flowers late, the kernels do not always mature before the end of the growing season, hampering routine seed yield evaluations of biotech traits introduced in B104 at many geographical locations. Therefore, we generated five hybrids by crossing B104 with the early‐flowering inbred lines CML91, F7, H99, Mo17, and W153R and showed in three consecutive years that the hybrid lines proved to be suitable to evaluate seed yield under field conditions in a temperate climate. By assessing the two main processes driving maize leaf growth, being rate of growth (leaf elongation rate or LER) and the duration of growth (leaf elongation duration or LED) in this panel of hybrids, we showed that leaf growth heterosis was mainly the result of increased LER and not or to a lesser extent of LED. Ectopic expression of the transgenes GA20‐oxidase (GA20‐OX) and PLASTOCHRON1 (PLA1), known to stimulate the LER and LED, respectively, in the hybrids showed that leaf length heterosis can be stimulated by increased LER, but not by LED, indicating that LER rather than LED is the target for enhancing leaf growth heterosis. To enable transgenic maize research, hybrids between the inbred B104 that can be routinely transformed and early flowering inbreds were evaluated for yield components in three consecutive years. In addition, we show that leaf elongation rate is the main contributor to leaf growth heterosis in these hybrids, which can even be stimulated by overexpressing GA20OXIDASE, a known regulator of leaf elongation rate. Although leaf elongation duration has a limited contribution to the growth heterosis, the effect of the ectopic expression of PLASTOCHRON1, known to enhance leaf elongation duration and leaf growth, is still observed in the hybrids. This detailed understanding of the growth processes driving heterosis will be key to further breed for high yielding hybrids.