Gibberellin Regulation of Amino Acid Transport, Metabolism, and Protein Accumulation in Developing Pea (Pisum sativum L.) Seeds
Creators: Giebelhaus, Johannes D
Publisher: name: University of Alberta Library
Year: 2023

<p>Global agriculture is currently under pressure to sustain the growing global population, and pulse crops like field peas could provide a greater portion of dietary protein to help offset pressures on sustainable crop production. Many field pea varieties have a mutation in the gibberellin (GA) biosynthesis gene PsGA3ox1 (le) which causes a decrease in bioactive GAs, a plant hormone that regulates growth and development. The le mutation in field pea leads to lower GA levels, producing shorter stemmed plants useful for cultivation; however, its effects on seed composition are not well understood. This study was undertaken to further understand the influence of GAs on pea seed development, focusing on its role in seed protein accumulation. Using a transgenic PsGA3ox1 (LE) overexpressing line (TG1) and its isogenic null line (C1), and conventionally bred LELE and lele lines, changes in seed tissue free amino acid and total nitrogen content were determined to identify potential GA-induced effects on processes that effect protein accumulation during seed development. Estimated cotyledonary protein content per seed tissue was elevated in the transgenic PsGA3ox1 (LE) line along with transcript abundance of genes encoding legumin A, vicilin, albumin 1 and albumin 2 during the seed-filling stage (12-20 days after anthesis; DAA), suggesting that seed storage protein accumulation is initiated earlier in seed tissues with elevated bioactive GA levels. Estimated cotyledonary protein content per seed was also higher in mature TG1 seeds compared to that in C1. Free amino acid pools declined in concentration in all seed tissues from 12 to 20 DAA, with lower total amino acid levels and earlier declines in concentrations of the key amino acids glutamine, glutamate, alanine, asparagine, homoserine, and threonine in TG1 seed coats and cotyledons than that in C1, indicating accelerated metabolism and recruitment of amino acids into seed storage proteins in the GA-elevated line TG1. The amino acid metabolism genes PsASNase2c (codes for an asparaginase that converts asparagine to aspartate and ammonia) and PsGS1a (codes for a glutamine synthetase that converts glutamate and ammonia to glutamine) function to maintain minimal levels of aspartate and glutamine, respectively, in seed tissues as precursors for synthesis of an array of other amino acids. Transcript abundance of PsASNase2c and PsGS1a increased earlier and for a longer duration in TG1 cotyledons compared to that in C1, indicating an earlier transition to the seed-filling stage in TG1 seeds. The embryonic transcription regulators PsABI3 and PsFUS3, that are involved in initiation of the transition to the seed-filling phase of development and the onset of seed storage protein biosynthesis, were elevated at 12 DAA in TG1 seeds indicative of an earlier onset of seed maturation stimulated by higher GA1 levels during early development. Overall, this research has identified candidate genes involved in key physiological processes affecting seed protein accumulation that are influenced by GA earlier in development, which could be targeted in breeding efforts to improve the seed protein content of conventional field pea varieties.</p>