Scientists Reveal that a MAPK Signaling Pathway Controls Grain Size

Researchers from the Chinese Academy of Sciences (CAS) and the University of Chinese Academy of Sciences reported that a MAPK cascade signalling regulates grain size in rice. The results are published in Molecular Plant.

MAPK signaling pathways have been known to have significant functions in multiple processes of plant growth and development and defense responses. The MAPK cascade contains at least three kinases: a MAPK kinase kinase (MKKK), a MAPK kinase (MKK) and a MAPK.

A previous study showed that loss-of-function mutant of OsMKK4 (smg1) forms small grains in rice. In the latest study, they identified a gain-of-function mutant of OsMKK4, which forms large grains. They also identified the smg2 mutant, which exhibits similar small-grain phenotype as smg1. SMG2 encodes OsMKKK10.

Overexpression of constitutively active OsMKKK10 leads to large grains. Biochemical analysis showed that OsMKKK10 could sequentially phosphorylate and activate OsMKK4 and OsMAPK6. Further analyses showed that enhanced activity of OsMAPK6 results in large grains, while decreased activity of OsMAPK6 leads to small grains. Genetic analysis showed that OsMKKK10, OsMKK4, and OsMAPK6 function in a common pathway to control grain size.

Their analyses revealed that OsMKKK10, OsMKK4 and OsMAPK6 act as a cascade to promote grain growth.

Read the news release from CAS for more information.