Abstract
BackgroundGrain weight (GW) is a key component of sunflower yield and quality, but may be limited by maternal tissues. Cell growth is influenced by expansin proteins that loosen the plant cell wall. This study aimed to identify spatio-temporal expression of EXPN genes in sunflower reproductive organ tissues (ovary, pericarp, and embryo) and evaluate correlations between reproductive organ growth and expansin genes expression. Evaluations involved eight different developmental stages, two genotypes, two source-sink treatments and two experiments. The genotypes evaluated are contrasting in GW (Alybro and confection variety RHA280) under two source-sink treatments (control and shaded) to study the interactions between grain growth and expansin genes expression.ResultsOvaries and grains were sampled at pre- and post-anthesis, respectively. Final GW differed between genotypes and shading treatments. Shading treatment decreased final GW by 16.4 and 19.5% in RHA280 and Alybro, respectively. Relative expression of eight expansin genes were evaluated in grain tissues. EXPN4 was the most abundant expansin in the ovary tissue, while EXPN10 and EXPN7 act predominantly in ovary and pericarp tissues, and EXPN1 and EXPN15 in the embryo tissues.ConclusionsSpecific expansin genes were expressed in ovary, pericarp and embryo in a tissue-specific manner. Differential expression among grain tissues was consistent between genotypes, source-sink treatments and experiments. The correlation analysis suggests that EXPN genes could be specifically involved in grain tissue extension, and their expression could be linked to grain size in sunflower.
Highlights
Grain weight (GW) is a key component of sunflower yield and quality, but may be limited by maternal tissues
Much less information is available about the role of EXPN in sunflower grain growth, this study aimed to address the following questions: i) are ovary and grain growth associated with EXPN expression at both pre- and post- flower fertilization? ii) is pericarp and embryo enlargement driven by different EXPN? iii) is the timing of EXPN expression similar for the pericarp and embryo? and iv) is the effect of EXPN on GW mediated by the abundance, rate, or duration of EXPN expression? To answer these questions, we identified the EXPN involved in ovary and grain growth by measuring mRNA gene transcripts and their time-course expression in field experiments
The correlation analysis supports the qualitative analysis and suggests that EXPN genes could be involved in grain tissue extension, and their expression could be linked to grain size in sunflower (Fig. 5)
Summary
Grain weight (GW) is a key component of sunflower yield and quality, but may be limited by maternal tissues. This study aimed to identify spatio-temporal expression of EXPN genes in sunflower reproductive organ tissues (ovary, pericarp, and embryo) and evaluate correlations between reproductive organ growth and expansin genes expression. The genotypes evaluated are contrasting in GW (Alybro and confection variety RHA280) under two source-sink treatments (control and shaded) to study the interactions between grain growth and expansin genes expression. The sunflower grain is an achene comprised of two main components: the pericarp (coat or hull), resulting from the fusion of the ovary tissues and part of the receptacle (maternal origin), and the embryo, formed by two cotyledons and a small stem and radicle, derived from the egg fertilization. The mature sunflower grain lacks endosperm (it is consumed during embryo growth), grain reserves (lipids, carbohydrates, and proteins) accumulate within embryo cells, mainly in the cotyledons [15]
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