Ovary morphology determines ovary-to-grain transition process and final grain weight potential in wheat

Abstract

The ovary-to-grain transition process is crucial for individual grain weight potential, but the but the physiological regulation of this highly dynamic and complex developmental process remains largely unknown unknown. Here, we performed a high temporal-resolution analysis of the proximal (large) and distal (small) ovaries/grains collected at an interval of 3 days from the booting stage to maturity stage. During grain-filling process, proximal grains always maintained a greater dry matter (0–36 days after anthesis, DAA), water (0–33 DAA), sugar (3–33 DAA), protein (6–36 DAA), and starch (amylose and amylopectin, 18–36 DAA) content, and larger volume (-15–36 DAA) than distal grains, but their partition or concentration did not differ between the proximal and distal grains. This result suggested that the capability of proximal and distal grains to produce water, sugar, protein, and starch within the same volume was similar; thus, grain sink (i.e. volume) was the cause in determinant of grain weight potential. In fact, the proximal ovary had a larger volume and related parameters (length, width and thickness) than the distal ovary before anthesis stage. in addition, the correlation coefficients of length and width with volume are higher than the correlation coefficients of thickness with volume. Clearly, we discovered a dynamic physiological mechanism for high proximal grain weight: the rapid elongation and widening of the proximal ovary improved its size, which passed to the proximal grain a volume advantage in the following ovary-grain transition, which allowed it to took up more sucrose and then converted into more starch and protein, improving dry matter accumulation and increasing proximal grain weight. Our findings provide a precise strategy for breeding and cultivation to increase individual grain weight potential by improving ovary volume.