Fig. 2: Reciprocal gene loss of the duplicated HWS pair causes abortive pollen and lethal embryos in hybrid progeny.

Transverse sections of anthers at various developmental stages from WYJ7 (a–f) and NIL-hws1^WYJ7/hws2^CG14 (g–l). St5, secondary sporogenous cell stage; St8, dyad stage; St10, vacuolated microspore stage; St11, bicellular pollen stage; St12, tricellular pollen stage; St14, mature pollen stage. E, epidermis; En, endothecium; MI, middle layer; T, tapetum; MMC, meiocyte mother cell; Dy, dyad cell; Msp, microspore; Bp, bicellullar pollen; Mp, mature pollen; Ap, abortive pollen. Scale bars = 20 µm. TEM observations showing anthers at St10 of WYJ7 (m, n) and NIL-hws1^WYJ7/hws2^CG14 (o, p). The photomicrographs with labels n1, p1 are enlargements of the areas enclosed by white dotted lines in n, p. E, epidermis; En, endothecium; Msp, microspore; T, tapetum; V, vacuole; Nu, nucleus; Ne, nexine; Te, tectum; Ba, bactum; Ub, Ubisch bodies. Scale bars = 10 µm (m, o), 5 µm (n, p), and 2 µm (n1, p1). q SEM images of the normal-shaped anther (q1, q3, q4) and normal pollen grain (q7) from WYJ7, and shrunken anther (q2, q5, q6) and invaginated pollen grain (q8) from a NIL-hws1^WYJ7/hws2^CG14 plant. Epidermal cells and regions of higher magnification (boxed) are shown in q3-q6. Scale bars = 100 µm (q1, q2), 10 µm (q3-q6), and 2 µm (q7, q8). Microscopic examination of developing (r-u) and mature embryo sacs (v-w) of WYJ7 (r, t, v) and NIL-hws1^WYJ7/hws2^CG14 (s, u, w). PN, polar nucleus; AC, antipodal cell; SC, synergid cell. Scale bars = 100 µm. All experiments were repeated independently at least three times of at least three plants, with similar results.