Nonhebel, H. | bioRxiv Science

bioRxiv2023

The Effect of 1-MCP on grain size and yield-related traits of Eragrostis tef

Teff is an Ethiopean cereal that has the potential for increased global production. However, as a very small-seeded grain, it experiences high levels of post-harvest loss. As ethylene is reported to have a negative effect on grain size, this study sought to test whether 1-methylcyclopropene (1-MCP), an ethylene action inhibitor, is a suitable molecule to improve grain size of teff as well as to determine the optimum application time and concentration. The 1-MCP treatment was evaluated on well-watered plants as well as plants subjected to moderate water stress, with the stress treatment imposed one week before the expected flowering date. Application of 1 PPM 1-MCP to individual panicles improved grain size and thousand-grain weight (TGW) by 22% and 29% under moderate water stress and 10% and 16% under well-watered conditions, respectively. It also increased yield per panicle. However, when applied to whole plants it was not effective, due to the extended flowering time of teff and differing responses of panicles at different developmental stages. These observations suggest that genetic modification leading to lower production of endogenous ethylene could benefit grain size in teff. However, 1-MCP treatment is unlikely to be effective in the field.

plant biology↗

bioRxiv2020

Reinvestigation of grain weight genes TaTGW6 and OsTGW6 casts doubt on their role in auxin regulation in developing grains

The THOUSAND-GRAIN WEIGHT 6 genes (TaTGW6 and OsTGW6) are reported to result in larger grains of wheat and rice by reducing production of indole-3-acetic acid (IAA) in developing grains. However, a critical comparison of data on TaTGW6 and OsTGW6 with other reports on IAA synthesis in cereal grains requires that this hypothesis be reinvestigated. Here, we show that TaTGW6 and OsTGW6 are members of a large gene family that has undergone major, lineage-specific gene expansion. Wheat has nine genes, and rice three genes encoding proteins with more than 80% amino acid identity with TGW6 making it difficult to envisage how a single inactive allele could have a major effect on IAA levels. TGW6 is proposed to affect auxin levels by catalysing the hydrolysis of IAA-glucose (IAA-Glc). However, we show that developing wheat grains contain undetectable levels of ester IAA in comparison to free IAA and do not express an IAA-glucose synthase. Previous work on TGW6, reported maximal expression at 20 days after anthesis (DAA) in wheat and 2 DAA in rice. However, we show that neither gene is expressed in developing grains. Instead, TaTGW6, OsTGW6 and their close homologues are exclusively expressed in pre-emergence inflorescences; TaTGW6 is expressed particularly in microspores prior to mitosis. This combined with evidence for high levels of IAA production from tryptophan in developing grains demonstrates TaTGW6 and OsTGW6 cannot regulate grain size via the hydrolysis of IAA-Glc. Instead, their similarity to rice strictosidine synthase-like (OsSTRL2) suggests they play a key role in pollen development.

plant biology↗